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Effect of welding motion and pre-/post-annealing of friction stir welded AA5754 joints
Abstract
An innovative approach to the friction stir welding process (defined by authors as RT-type configuration) of AA5754 sheets, characterized by a welding motion of the pin tool obtained by the combination of two different movements occurring simultaneously, was developed. Such novel approach was compared with the conventional friction stir welding process (T-type configuration). Tools with different pin heights were used in order to obtain different sinking values. Finally, the influence of the annealing treatment, prior and after the friction stir welding process, was studied. The effect of process parameters and annealing treatment on the microstructure, micro- and macro-mechanical properties of friction stir welded joints obtained under RT-type and T-type configurations was widely investigated. This way, the process condition and the temper state that allow obtaining defect-free joints, without the occurrence of the oxide defects of kissing-bonds, and faint zigzag line pattern in the NZ, was defined. It resulted that a pin deviation by R = 0.5 mm, from welding centerline, in the post-welded annealed condition, showed better tensile strength, respect to the conventional (T-type) welding.
... Two of the most promising optimization means for FSW refer to the metallurgical status of the joining materials, and to the FSW tool itself (chiefly the pin). Both of these issues are the object of the present work, which aims at showing the technological potentialities of making a homogeneous and highly resistant FSW joint through material thermal treatment optimization, on one hand; and on the other, at modifying the pin geometry, FSW settings and pin orientation with respect to the joining plates [15][16][17][18][19]. This manuscript focused on new FSW methodologies applied to light alloy plates, such as aluminum and magnesium, and to dissimilar metal plates (namely, aluminum + magnesium). ...
... Formation of the kissing-bond is related to the insufficient break-up of oxide layer by an insufficient stretch of the contacting surfaces around the welding probe. This in turns can be formed by low heat-input parameters [18,20]. Moreover, FSW induced stress and strain rate, which are primarily generated by the pin and the shoulder motions across the sheet/plate, are the main technological terms for the design optimization of pin and shoulder. ...
... In this framework, Cabibbo et al. developed an innovative approach to the conventional FSW process, defined by authors as RT-type configuration, in which the welding motion of the pin tool was obtained by combining two different movements occurring simultaneously [18]: (i) the rotation of the pin axis around an axis, perpendicular to the sheet blanks and belonging to the welding line, with a radius equal to R, and (ii) the translation of the pin axis along a direction parallel to the welding line ( Figure 6). Two different R values, equal to 0.5 and 1 mm, were considered. ...
Friction stir welding (FSW) is the most widely used solid-state joining technique for light-weight plate and sheet products. This new joining technique is considered an energy-saving, environment friendly, and relatively versatile technology. FSW has been found to be a reliable joining technique in high-demand technology fields, such as high-strength aerospace aluminum and titanium alloys, and for other metallic alloys that are hard to weld by conventional fusion welding. Several studies accounted for the microstructural modifications induced by solid-state FSW, based on the resulting mechanical properties obtained at the FSW joints, such as tensile, bending, torsion, ductility and fatigue responses. In the last few years with the need and emerging urgency to widen the FSW application fields, broadening the possible alloy systems, and to optimize the resulting mechanical properties, this joining technique was further developed. In this respect, the present contribution focuses on two modified-FSW techniques and approaches applied to aluminum alloys plates. In a first case, an age-hardening AA6082 sheets were double side friction stir welded (DS-FSW). In a second case a non-age-hardening AA5754 sheet was FSW by an innovative approach in which welding pin was forced to slightly deviate away from the joining centreline (defined by authors as RT). In both the cases different pin heights were used, the sheets were subjected to heat treatments (peak hardening T6 for the AA6082, and annealing for the AA5754) and compared to the non-heat treated FSW conditions. Microstructural modifications were characterized by optical microscopy (OM). The mechanical properties were characterized both locally, by nanoindentation techniques, and globally, by tensile (yield, YT; ultimate, UT; and elongation, El) or forming limit curve (FLC) tests. Both the new approaches were directly compared to the conventional FSW techniques in terms of resulting microstructures and mechanical responses.
... The scientific literature reports that FSW process results in intense plastic deformation and temperature distribution within and around the stirred zone of the workpiece. Very complex mechanisms occur during the weld formation, due to thermal and micro-and macro-mechanical effects influenced by the different process parameters [55][56][57][58]. For this reason, the FSW process parameters, such as the TP, ω and v values, must be carefully selected in order to guarantee an efficient and successful welding operation [46,50,59]. ...
... As a matter of fact, it can be observed in Figure 6 that the low-strength heat affected zone locally elongated, resulting in necking and fracture, whereas the nugget zone experienced only a very small strain. and macro-mechanical effects influenced by the different process parameters [55][56][57][58]. For this reason, the FSW process parameters, such as the TP, ω and v values, must be carefully selected in order to guarantee an efficient and successful welding operation [46,50,59]. ...
Friction stir welding (FSW) is a well-established welding technique, which allows joining abutting surfaces by generating heating through a rotating and translating tool specifically shaped. Differently from the conventional techniques, continuous welding processes can be executed by FSW, thus supporting the economy of scales objectives. This paper deals with the selection of the optimal process parameters for the FSW of the AA6082 aluminum alloy. Three welding parameters, namely tool plunging, rotational speed and welding speed, have been handled as independent variables for developing two mathematical models by means of a non-linear regression-based approach, with the aim of predicting both ultimate tensile strength and ultimate elongation of the welded joints. A set of additional experimental tests has been used to validate the mentioned metamodels and finally three different metaheuristic algorithms have been implemented for selecting the best process parameters able to maximize the aforementioned mechanical properties. A comparison analysis based on further experimental tests confirmed the accuracy of the predicting metamodels and the quality of solutions yielded by the proposed optimization approaches.
... A further novel approach to the FSW process (defined by authors as RT-type [13]) is also here reviewed. This new configuration consists on a combination of different plate-to-pin motions. ...
... The RT-type and T-type FSW were performed using a pin rotational speed, ω = 2000 rpm, a transverse speed, v = 30 mm/min, and a tool plunging speed of 1.5 mm/min. The above reported setting parameters were chosen by an optimization FSW processing study reported both some of the present authors in [13]. ...
The present contribution reports on the cutting-edge research activities performed by the authors in the field of innovative manufacturing processes applied to advanced light alloys. These include Friction Stir Welding (FSW), Friction Stir Extrusion (FSE), and Additive Manufacturing (AM). Two new FSW configurations are here introduced and described. A first double-side friction stir welding (DS-FSW), where the welding is performed on both sheet surfaces, one after the other. A second rotating tool FSW (RT-FSW), in which pin is made to rotate around its centerline welding direction, by 0.5 and 1.0 mm. The feasibility of solid-state recycling of a case study, such as an AA1099 machining chips, is exploited using FSE process. In addition, in order to optimize the die design and the process parameters, finite-element (FE) simulation of the process was carried out. The game-changing potential of the metal AM technology is un-veiled through results obtained on light alloys for biomedical applications produced by Powder Bed Fusion (PBF).
... The yield strength, y , response corresponds, to some extent, to the ultimate strength, U , among the three different experimental conditions, i.e. between the FSW and FSW + CR. The here reported mechanical responses are in good agreement with previous reported results on same alloy, but different welding parameters [12][13][14][15], and on different aluminium alloys [16][17][18][19][20][21][22]. The ductility-to ultimate strength relationship here observed, was properly addressed by applying formability tests to the BM, FSW, and FSW + CR conditions. ...
... The hardness were recorded at the midheight of the FSW section, in the FSW, FSW + CR, and FSW + A + CR experimental conditions. Some authors [13][14][15][19][20][21][22] also studied the role of the FSW parameters and that of the post-FSW thermal treatments on the hardness profiles across the FSW joint section. The here reported results are ...
Among different welding techniques currently available in the market, friction stir welding (FSW) is surely considered as an effective and reliable joining technique. Friction stir welds are characterized by lack of voids, cracks and distortions, as the technique does not involve any material fusion. The grained structure of the weld joint is generally finer than the base material. In particular, the nugget zone (NZ) experiences a dynamic recrystallization process during FSW that generally guarantees a stable very-fine grained structure. In the present study, the effect of cold rolling (CR) on the formability limits, the resulted microstructure, and mechanical response of FSW but joint was investigated. To this purpose, an AA5754 aluminium alloy was used. The FSW was performed with rotational and welding speeds equal to 1200 rpm and 100 mm/min, respectively, and an initial tool sinking of 0.1 mm. Strips extracted from the FSWed sheets were CR, with the rolling direction perpendicular to the welding line. Two setups were used in the CR experiments. One, conventional to determine the formability limit of the FSW AA5754 sheet; a second one performed in a CR set-up designed to induce an equivalent strain of about 1, in a single passage through the CR gage. This was aimed to make the post-FSW CR able to induce a further grained structure reduction within the NZ.
... The shear plastic deformation induced into the alloy during the ECAP first pass is also responsible for a large tangled dislocation density in the grains and cells interior. These will rearrange and reorganize to form low-angle boundaries, and thus new cells under following passages into the ECAP die [15][16][17]20,21]. On the other hand, the FSW NZ was characterized by an almost equiaxed grain structure containing quite low-density of tangled dislocations within the grains. ...
... In this latter case, the grains were formed by a thermo-mechanical stirring process acting in the NZ. This ultimately induced a recrystallization process on the existing alloy microstructure [21][22][23][24][25][26]. This aspect is one of the key deformation mechanisms that differentiate a grain-refinement process induced by friction stir process (FSP) from a grain-refinement generated by ECAP. ...
Friction stir welds are considered reliable joints for their lack of voids, cracks and distortions. When compared to the base material, friction stir welding (FSW) joints typically exhibit finer grain structured (especially at the nugget zone, NZ). Similarly, refined grain structure can also be obtained by severe plastic deformation (SPD) techniques, such as equal channel angular pressing (ECAP). In fact, the fine grain structures produced within the NZ of FSW or friction stir processed (FSP) materials are usually coarser than the ones achieved by ECAP. The former is characterized by lower dislocation density, higher high-angle boundary fraction and different mechanical strength, compared to what can be obtained by ECAP. In this study, a dedicated cold-rolling (CR) set-up, specifically designed to simulate an ECAP-equivalent shear deformation, was used to further refine the grain structure of FSW AA5754 sheets. The effect of ECAP-equivalent deformation induced by CR in a 2 mm-thick AA5754-H111 FSW joint was investigated. FSW was carried out at two different rotational (ω) and translational (v) welding speeds, 600 rpm, 200 mm/min and 1800 rpm, 75 mm/min, respectively. FSW sheets were then CR to obtain an equivalent shear strain of ε ~ 1.08, that is equivalent to 1-ECAP pass carried out with an internal die channels intersecting at an angle φ = 90° with a curvature extending over an angle Ψ = 20°. By CR, the sheet thickness reduced only by ~20%. The role of annealing on the FSW and CR plastically deformed AA5754 was also investigated. This was applied either prior or after FSW, and it resulted that whenever it follows the FSW, the mean volume fraction of dispersoids and Mg-rich particles is higher than the case of annealing preceding the FSW process. On the contrary, it was found that the annealing treatment had a minimal role on the dispersoids and particles mean size. The here reported post-FSW ECAP-simulated deformation, obtained by a customized CR process, showed sheet integrity and a significant concurrent grain size refinement.
... The R-ratio represents the maximum load per unit of weld length that samples can withstand prior to fracture and is calculated using Eq. 1. The term "Weld efficiency" is used to refer to the ratio of relative strength of a welded metal to the strength of the base metal [29], which is calculated using Eq. 2. It should be noted that the strength of welded aluminum joints for aluminum alloys is always less than the strength of the base material mainly due to heat input where we lose the as-received temper of the material [30]. In the case of AA5052-H32, the material goes from the cold-worked (relatively high strength) H32 Content courtesy of Springer Nature, terms of use apply. ...
AA5052 is a widely used aluminum alloy in the automotive industry due to its excellent weldability, mechanical properties, and corrosion resistance. This study aims to optimize the parameters for wobbling overlap laser welding of dissimilar thickness aluminum AA5052-H32 sheets. The investigated parameters include laser power, travel speed, focal position, oscillation shape, and oscillation amplitude. The results reveal that the oscillation pattern has a minimal effect on mechanical strength. Additionally, the power intensity range of 13.2-20 J/mm 2 has been identified to ensure that weld efficiency remains above 89.9%. However, considering the significance of the undercut value for achieving a smoother weld line, it is necessary to maintain the oscillation amplitude at a minimum value of 1.5 mm. The microhardness pattern proves to be a valuable method for detecting defects such as underlying porosities and deflection caused by excessive thermal input on the top sheet. The optimized processing parameters for 1-1.5 mm thickness aluminum AA5052-H32 are determined as 2500 W, 5 m/min, 6.0 mm, and 1.5 mm for laser power, travel speed, focal position, and oscillation amplitude, respectively.
... The cross-sectional surface area of the welded region was taken from the middle of the length transverse section and etched before mounting on SEM as shown in figure 7 and figure 8. The microstructure of the weldment is shown in figure 7 with less defect and voids [10]. Which shows the greater and distinguishable grain size with boundaries at 20micron resolution. ...
... Aluminum alloys are widely used in the automobile, marine, and aerospace industries, as they are lightweight and have good wear resistance, corrosion resistance, and high impact strength [1][2][3][4][5][6][7][8]. Welding is the most common technique for joining aluminum alloy parts. ...
Lightweight aluminium alloys are widely used in many industries due to their advantageous mechanical properties. As welding is a popular method for joining aluminium alloy sheets, it is important to understand how the welding process affects the alloy’s performance. Here, we investigated the influence of various operating parameters during pulsed metal inert gas (MIG) welding of thin aluminium alloy plates on the input energy and metallurgical microstructure of the weld. A series of welding tests were performed using surface welding of AA6061 aluminium alloy plates under conditions of a single strong-pulse, single weak-pulse, or double pulse. The morphology, metallurgical structure, and hardness of the welds produced using the different welding parameters were then examined. We observed that increasing the welding speed and the arc duration of low-energy pulses can reduce the heat input. Lower heat input is advantageous as it results in a higher cooling rate of the welding pool and a smaller average grain size of the weld structure. In addition, increasing the welding speed increased the hardness of the weld. Double pulsed MIG welding showed the best overall weld performance and is recommended for improving the quality of aluminium alloy bonding.
... However, the combination of friction stir welding, heat treatments, and other plastic deformation-based techniques such as cold rolling, which can minimize the welding sheet thickness reduction in the welded joint and have a strengthening effect that improves the overall efficiency of the final joint, is worth further investigation [17][18][19][20][21]. Indeed, currently the thinning of the weld is addressed with special tools or welding additive equipment [22]. ...
Friction stir welding (FSW) has now reached a technological impact and diffusion that makes it a common joining practice for several classes of metallic materials. These include light alloys (aluminum, titanium, magnesium), steels, and other metallic alloys. In addition, the combination of FSW with pre- or post-welding heat treatments or plastic deformation, such as cold rolling (CR), can favor minimal necessary plate thicknesses and induce effective alloy strengthening mechanisms that make the FSW joint lines as plate reinforcing zones. Process parameters, such as pin rotation and transverse speed, can be tuned to optimize the mechanical properties of the resulting joint. This work presents a microstructural study of the mechanical response of different sequences of heat treatment, FSW, and CR in a non-age hardened Al-Mg AA5754 alloy. By using polarized optical microscopy and microhardness tests, two FSW conditions were used to fabricate a joint; and were than subjected to different sequences of heat treatment and cold rolling. The results suggest that FSW conditions have a limited effect on the microstructure, while microhardness profiles show a higher variability of the different datasets related to the low welding speed investigated.
... This, in turn, jeopardizes the weldment surface to undergo delamination and decohesion. [17] To overcome these defects, there is a need to reduce the weaving radius by designing novel geometry with reduced step size for weaving motion. The objective of this work is a novel study on geometric tool path pattern with a square wave of varying step size and to obtain sufficient dynamic recrystallization with the formation of equiaxed grains. ...
The proposed study deals with the joining of AA6061 T6 alloy using a novel geometric square wave tool path pattern for adequate mixing of materials with increased stirring time and enlargement of the deformation zone. Experiments were conducted based on the process parameters to imply the stirring effect like rotation speed 1200 rpm, weaving rate 100 mm/min; and specific step sizes (1.0, 1.5, and 2.0 mm). Results show that the Percentage of variation for achieving the higher tensile strength of 11.3%, micro vickers hardness of 12.8% with a step size of 1 mm compared to the linear weldment. The SEM morphologies of the weldment clarify the formation of IMCs like spheroidal cementite with the zeolitic structure for resulting in higher hardness value. The EDAX results confirm the formation of intermetallic precipitates like Mg2Si that leads the precipitation hardening and grain boundary strengthening.
... The importance of Tool Path Profile Design (Eccentric weave) was revealed. The rotation of the pin about its axis, and the translation of the pin along the axis did avoid weld defect [13]. From the above literature and research gap, in this present investigation, stirring was achieved through tool pin eccentricity. ...
Structural materials such as copper and aluminium, with comprehensive properties such as excellent thermal and electrical conductivity, are used in engineering applications. Despite the beneficial actions of aluminium and copper as a composite structure, the development of such dissimilar combinations is more difficult. Some unsolvable problems such as oxidation, tunnels, and fragmentary cracks include the fusion of dissimilar metals or alloys in the joining of Cu and Al alloys using classical methods such as fusion welding and pressure welding. The Friction Stir Welding (FSW) process has been found to be an effective method for joining different metals/alloys in solid-state joining technology to solve these problems. A non-consumable stirring tool is plunged into the base metal joints comprising a profiled pin and shoulder and is made to move in a predefined direction to stir up the bondage between the base metals. A proper stirring of base metals was achieved by tool pin eccentricity in this current investigation.
... According to Yuqing et al. [6], tool pin offset for joining of thick plates of aluminium alloy reported better stirring action and an easy flow of plasticised material in the weld nugget. Cabibbo et al. [7] studied the effect of pin rotation around its axis is normal to the weld line and identified that the translation of the pin along the axis would overcome the formation of the oxide layer and avoids a severe weld defect. ...
The friction stir welding technique is currently employed for different alloy combinations like magnesium, titanium, copper, nickel-based composites. Dissimilar materials may be efficiently joined by the process and this has been used in several structural applications such as automotive components, aircraft structure, shipbuilding, and space shuttle external tank and train bodies. Even though improvement in the joint strength was achieved, problems such as voids, tunnels, cracks persisted in the weldments. The objective is to achieve defect-free joints. Tool pin offset for joining of aluminum alloy enables better stirring action and an easy flow of plasticised material in the weld nugget. Hence, to overcome the above-mentioned problem, a technique of combined effect of weaving, tool pin offset, and reinforcement of self-lubricated graphene nanoplatelets was attempted. The tensile strength obtained with the effect of tool rotational speed under weave weld with pin offset condition with reinforcement was 13.82 % higher than the weld obtained under the same condition without reinforcement. IMCs such as AlCu, Al2Cu, and Al4Cu9 large size band layers were observed with the linear welding condition, whereas weave welding conditions resulted in the formation of the thin uniform layer.
... So the prior heat treatment of friction stir tailor-welded aluminum joint base metal is one important key parameter that should be considered in the welding process. Accordingly, a number of research papers have been published on post-weld heat treatment conditions of friction stir tailor-welded aluminum joints [11][12][13]. However, only a few researchers had investigated the effect of pre-weld heat treatment conditions of base metal on microstructural and mechanical properties of friction stir weld aluminum alloys [14][15][16][17][18][19]. ...
The heat treatment of friction stir tailor-welded aluminum joints is one important key process to improve the efficiency of joint strength and ductility as well as fracture locations, since almost all of the welded parts are subjected to a forming process. Therefore, the effect of heat treatment on microstructural characterization and mechanical properties of welded joints is a very important research area to improve the nugget zone in welded structures of aircraft segments. The objective of this study is to investigate the effect of changing pre-weld heat treatment conditions (first case: solution heat treated with artificial aging (T6) and second case: annealed heat treatment (O)) by microstructural characterization with an optical microscope, scanning electron microscope and x-ray diffraction and mechanical properties using micro-hardness, tensile and bending tests. After that, ANOVA was used in order to determine the interaction effect between the conditions of heat treatment (T6 and O) and interlayer strip widths. The results revealed that the softened zone of FSW joints in the annealed condition (O) was relatively more homogeneous than FSW joints from solution heat treated and artificially aged (T6). On the other hand, the strength efficiency of FSW joints from annealed (O) samples was the higher value than the joints efficiency at solution heat treated and artificially aged (T6). Furthermore, the annealed (O) FSW joints fractured in the base metal, while FSW joints from solution heat treated and artificially aged (T6) samples fractured in the HAZ. The microstructure and mechanical properties of weld nugget zones were influenced by the pre-weld heat treatment conditions. Finally, the results of ANOVA agreed with the results of mechanical properties.
... Yang et al. studied the effect of pre-and post-heat treatment on mechanical properties and microstructures in friction stir welding of dissimilar age-hardenable aluminum alloys [14]. Cabibbo et al. developed an innovative approach to the FSW process of AA5754 blanks, characterized by a welding motion of the pin tool obtained by the combination of two different movements occurring simultaneously, and studied the influence of annealing, prior and after welding [15]. ...
The high-speed deformation behavior of friction stir-welded thin sheets in AA6082-T6 aluminum alloy, under biaxial balanced stretching, was investigated by means of a hemispherical punch test carried out using direct tension-compression Split Hopkinson Bar. The friction stir welding process was performed on thin sheet blanks using a pinless tool; the rotational and welding speeds were kept constant during process. The dynamic tests were carried out, with a punch speed of 4500 mm/s, at different punch stroke values until failure of the friction stir welded sample. It was seen that failure occurs along the welding line at a dome height about 11% higher than that at the onset of necking. Fractographic analysis shows that deformation is localized in the fracture zone. The results were compared with those obtained on friction stir welded blanks deformed under quasi-static condition in order to evaluate the influence of the loading rate on the weld deformation and fracture mechanisms. It was shown that joints deformed under dynamic loading condition are characterized by a dome height at the onset of necking significantly higher than the one measured under quasi-static condition.
... [6][7][8][9][10] It is thought that FSW consumes less energy as compared with fusion welding technologies due to the lower temperatures involved and the solid-state nature of the process. [11][12][13][14][15] Heurtier et al. found that the heat inputs for gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) are 2 and 1.5 times higher than that for FSW, respectively. 16 Furthermore, FSW leads to a decrease in material waste and avoids radiation and dangerous fumes. ...
The life cycle assessment (LCA) methodology was used to evaluate the environmental impact of friction stir welding (FSW) of AA5754-H114 aluminium alloy sheets. FSW was performed under different values of rotational and welding speeds to analyse the influence of the process parameters on midpoint category impacts. Pin tool wear and mechanical properties of joints were also evaluated. The functional unit chosen was related to the weld efficiency; furthermore, the weld length was set equal to 170 mm. The pre- and post-processing stages were also considered. Raw materials, energy and all inputs associated with each stage of product life cycle were collected and evaluated to analyse the environmental impact index. The results showed that, irrespective of the rotational speed, the lowest welding speed investigated leads to the highest energy consumption and, consequently, to the highest values of the midpoint category impact. On the contrary, at the highest welding speed, the environmental impact assumes the lowest values. By concerning the rotational speed, its effect on the midpoint category impact is strongly reduced compared to the one given by the welding speed. A performance index, obtained by considering both the midpoint category impact and ultimate tensile strength of the joints, was also defined.
Finally, the environmental sustainability of FSW was compared to the one of two different fusion welding technologies, namely gas tungsten arc welding (GTAW) and laser beam welding (LBW). The results showed that FSW was characterized by midpoint category impacts much lower than those of the GTAW, whilst such discrepancies decreased with the LBW.
... Since FSW is carried out in the solid state, all problems from solidification process are eliminated. Also, compared with the conventional fusion welding processes, the residual stresses and distortion are very low due to low heat input [2][3][4][5][6]. AA6061 is a typical alloy of 6xxx series and includes some alloying elements such as Al-Mg-Si [7]. ...
T
HE aim of the present work is to study the effect of rotation and welding speeds as well as
the T4 and T6 post-weld heat treatments (PWHT) on the corrosion behavior of AA6061-O
aluminum plates joined using friction stir welding (FSW). The corrosion properties of welded
joints were studied by Potentiodynamic polarization and Immersion tests. The results showed
that both T4 and T6 PWHT improves the corrosion resistance of stirred zones compared to base
alloy. However, joints of T4 showed lower corrosion resistance compared to T6. Increasing
welding speed or reducing rotation speed increased the corrosion resistance of joints.
... NZs' microstructures, shown in Figure 5, have shown complete transformation of the grain structure from the longitudinally elongated grains into finer equiaxed grains. This transformation was discussed by many researchers [22][23][24]and it is a stable believe that it happens due to material subjection to sever heat and plastic deformation resulting from the nature of the welding process at the NZ. Where dynamic recrystallization of the grains is the most recognized mechanism forms the grain structure in the NZ [4,15,25]. ...
... The absence of macroscopic defects such as voids, cracks or discontinuities in SZ means that FSW was successful in joining these dissimilar alloys. In addition, a basinshaped SZ is evident at the center of the FSW joint, which is extended from the bottom to the top surface of the sheet because of the friction induced between [18][19][20]. One can easily notice the patent transitions between the base metals and the nugget on both AA1050 and AA5083 alloy sides, as shown in Figs. ...
Metallurgical structure, mechanical properties and electrochemical behavior of dissimilar friction stir welding (FSW) between structural AA5083 and AA1050 alloys were investigated in this study. Optical microscopy and field emission scanning electron microscopy observations showed that the nugget zone (NZ) possesses equiaxed recrystallized grains of the two alloys with a flowing shape. Energy-dispersive spectroscopy analysis revealed that NZ is mainly composed of the advancing side alloy. The ultimate tensile and yield strengths of the dissimilar FSW joint were higher than those of AA1050 and lower than those of AA5083. Consequently, fracture occurred on AA1050 side during the tensile tests. The potentiodynamic polarization (PDP) results revealed that the passive current density of the FSW joint was in between that of AA1050 and AA5083. A modified Randles equivalent circuit was used to simulate the obtained experimental data of electrochemical impedance spectroscopy measurements. The acquired impedance parameters were in good agreement with the PDP measurements.
... Welding is a major fabrication method and widely used to join materials through a fusion process. Metallic materials are mainly considered in welding due to their excellent features and properties [1][2][3]. Numerous metallic materials can be joined using various welding techniques, including friction stir welding, friction stir spot welding, ultrasonic welding, gas tungsten arc welding, laser welding, gas metal arc welding, and arc stud welding (ASW). All of these methods have different advantages and disadvantages in terms of cost, appropriateness, labor, training, efficiency, time, temperature, and simplicity [4][5][6][7][8][9]. ...
In order to investigate the structure of welds, austenitic stainless steel (SS) studs with a diameter of 6 mm were welded to austenitic SS plates with a thickness of 5 mm using an arc stud welding (ASW) method. The effects of the welding current, welding time, and tip volume of the stud on the microstructure and ultimate tensile strength (UTS) of the welded samples were investigated in detail. The formation of δ-ferrites was detected in the weld zone because of the higher heat generated during the welding process. Higher welding current and time adversely affected the stud and significantly reduced the UTS of the samples. The UTS of the joints was also estimated using artificial neural network (ANN) and Taguchi approaches. The mathematical formulations for these two approaches were given in explicit form. Experimental results showed that the neural network results are more consistent with experimental results than those of the Taguchi method. Overall, it can be concluded that in order to achieve good welding joints and high strength values, ASW parameters should be investigated properly to determine the optimum conditions for each metal.
... Lightweight engineering alloys serve an important role in aerospace, automotive, and naval industries, for energy-saving and improved maneuverability [1,2]. Steels are progressively substituted by lightweight engineering alloys in these applications [3,4]. Among various lightweight engineering alloys, aluminum alloys have attracted considerable attention, due to their exceptional machinability, acceptable strength, and excellent anti-corrosion properties [5,6]. ...
Aluminum alloy welding suffers from problems such as solidification cracking and hydrogen-induced porosity, which are sufficiently severe to limit its potential applications. Because mitigated porosity incidence and solidification cracking are observed in aluminum welds using double pulsed gas metal arc welding (DP-GMAW), a comprehensive review of the mechanism is necessary, but absent from the literature. The oscillation of arc force and droplet pressure causes a weld pool stir effect. The expansion and shrinkage of the weld pool cause unusual remelting and resolidification of the previously solidified metal. DP-GMAW has an increased solidification growth rate and cooling rate, compared with conventional pulsed welding at same heat input. Both numerical and experimental results reveal the remarkable concept that refined microstructure in the fusion zone is obtained by using DP-GMAW. The mechanism of microstructural refinement is revealed as a weld pool stir effect and increased cooling rate. Hydrogen bubbles easily float out and then release from the weld pool originated from the weld pool stir effect. Reduced solidification cracking is achieved due to the refined solidification structure that originated from the increased cooling rate. The advantages, evolution process, and future trend of DP-GMAW are discussed.
... Cabibbo et al. [7] had done their research on the effect of pre and post-annealing & the welding motion of friction stir welded AA5754 joints. In this research, an innovative approach has been followed in the friction stir welding of the sheets of AA-5754 aluminium alloy. ...
An attempt has been made to summarise most of the aspects of FSW (friction stir welding) process and the advancements that have been made till the current time. The macro-structural and the micro-structural properties of the FSWed joints have been discussed. The variations in the process discussed in this review paper are: variation of the downward force, variation of the probe angle, length of probe, shape of shoulder, rotational speed of the tool, pin profile, traverse speed and working conditions. The setups used in majority of places consist of vertical milling machines. From the different pin profiles: WPP, TTP and PTP, that have been reviewed here, the PTP was found to be the best to get highest values of yield and tensile strengths on macroscopic scales. The joint strength has been observed to increase between the dissimilar materials on introducing a third foil of roughly one-Tenth thickness, between the two sheets of dissimilar material to be joined, in case of lap joint. The value of thermal co-efficient of expansion for the filler metal sheet must lie between the values of the thermal expansion coefficients of the materials of the sheets to be joined. The incorporation of friction stir welding in automobile industries and aviation industries is truly doing wonder by reducing the weight of the components without compromising the strength. In addition to high strength, the friction-stir welding process also eliminated the need of any filler material. This review paper can be beneficial for the future research work by minimising the cost as well as time because of the already investigated empirical relations that have been discussed here.
... Excellent fusion formations were produced at the sidewalls of the groove and the interlayers without any patent defects, such as holes, inclusions, or macrocracks. Homogeneous distribution of the particles was seen in the weldment [15]. ...
This study deals with the retrofication of micro and macro structural defects in joining aluminum and copper alloy using eccentric weave friction stir welding. In addition, graphene nano particles were added to strengthen the weldments. Welding experiments were conducted with two types of stir tool as (normal and offset pin) in linear and eccentric weave pattern. Results from this study reveal the possibility of tool tribology on eccentric stirring with tool pin offset producing a very minimal wear of 5 µm in comparison to other patterns of weld; defects on microscopic and macroscopic view of the weldments prove the existence of fragmental cracks in eccentric welding, mechanical properties viz. yield strength of 187 MPa, Ultimate tensile strength of 217 MPa, and elongation of 10% were found for the eccentric weave welded joints. This reveals the achievement of robust welded joints in the Aluminium and copper alloys by eccentric weave welding with pin offset.
... A further novel approach to the FSW process (defined by authors as RT-type [21]) is also reported. This new configuration consists of a combination of different plate-to-pin motions. ...
Friction stir welding (FSW) is a technique able to guarantee welding advantages such as the easy control of tool design, rotation speed, and translation speed. This is also a reason for a continuous research activity to optimize the effect of the different welding parameters and tool-metal setups. In this contribution, two innovative welding methodologies are presented and discussed. A first new FSW configuration was defined
as double-side friction stir welding (DS-FSW). In the DS-FSW, the welding is performed on both sheet surfaces, that is, the first welding is followed by a second one performed on the opposite sheet surface. In this chapter, the effect of the welding parameters, tool configuration and sheet positioning on the yield, ultimate strength, and ductility of an aluminum plate, its microstructure and its post-welding formability are discussed. A second new FSW configuration consists of a pin rotation around its centerline welding direction by 0.5 and 1.0 mm. This was defined by authors as RTtype configuration and it is characterized by a welding motion of the pin tool obtained by the combination of two different movements occurring simultaneously.
In the present paper, different types of pre- and post-weld treatments performed on aluminium alloys have been reviewed. Aluminium is the second most widely produced material after steel. Aluminium alloys can be welded using fusion welding techniques but they distort the weldments’ microstructure and the welds are prone to oxidation, porosity and cracking. Therefore, modern welding techniques like laser beam welding, electron beam welding and friction stir welding are now performed on aluminium alloys. Further, treatments like reinforcement, pre-weld and post-weld heat treatment and cryogenic treatment have also been performed by researchers and discussed in the paper. The application of various treatments has significantly improved the aluminium alloy weldments’ properties especially cryogenic treatment. The effect of preheat and cryogenic treatment on microstructure and mechanical properties of aluminium alloys’ weldments has not been researched properly and they require more attention of researchers.
The present work investigates the influence of post-weld heat treatments (PWHT) on friction stir welded joints of AA2014 and AA7075 dissimilar alloys. Four different PWHT conditions, namely artificial aging (AA), solution treatment and artificial aging, solution treatment (ST), and natural aging (NA), were applied to study their influence on weld strength and microstructural properties. Natural aging showed the best strength of 347.5 ± 7.78 MPa among all the PWHT conditions. In contrast, other PWHT conditions deteriorated the tensile strength compared to as-welded joints. The highest elongation of 10.76 ± 1.27% was observed in NA, while the lowest was in AA among all the welded joints. The fracture location shifted to the stir zone (WNZ) in AA and ST. In contrast, in other PWHT welds, fractures occurred outside the weld region. Abnormal grain growth was observed in the WNZ of the ST joint. Microhardness improvement was observed in WNZ of ST and NA weld, while a lower value was found in the remaining ones. Fracture study revealed that fracture mode was brittle in AA whereas ductile in other joints.
Dissimilar friction stir welding of AA5083-AA6061 alloys in different cooling environments (air, liquid nitrogen, and water) was successfully employed as an alternative method to enhance corrosion resistance and mechanical properties. The evolution of microstructure, corrosion behavior, and mechanical properties of friction stir welded joints were studied using optical microscopy (OM), electron backscattered diffraction, scanning electron microscope, electrochemical workstation, and universal testing machine. The results indicated that the width of the stir zone and grain size of heat-affected zones were reduced by the use of external cooling media. Electron backscattered diffraction results showed that the grain size in air-cooled friction stir welding, nitrogen-cooled friction stir welding and water-cooled friction stir welding were 7.6 µm, 4.5 µm, and 3.2 µm, respectively, and water-cooled friction stir welding joint developed a larger fraction of high-angle grain boundaries at stir zone. The intermetallics formed in the joints using cooling media were finer compared to that of the air-cooled samples. The corrosion behavior of the stir zone was impacted by the cooling environment while potentiodynamic polarization results revealed that the water-cooled friction stir welding joint showed excellent corrosion resistance due to the finer size of intermetallics. The minimum hardness values shifted to the stir zone in the case of nitrogen-cooled friction stir welding and water-cooled friction stir welding from the heat-affected zone location as in the air-cooled friction stir welding joint. For the joint made with water-cooled friction stir welding, maximum yield strength was obtained with a joint efficiency of 96% relative to AA5083 base material.
Electrochemical Micromachining (EMM) is a non-conventional technique that has the potential to provide excellent accuracy due to its ionic dissolution nature. The technique is evolving rapidly with continuous research works and emerging as a frontline technology in the micro-fabrication domain. The dominant input factors of electrochemical machining (ECM) process become very sensitive at micro-domain and parametric optimization is inevitable for enhanced performance. New researches are required to enhance every aspect of the processing system that includes electric power, electrolyte, feed mechanism, gap control etc. The aim of the current work is to produce micro-holes on SS-304 sheet using tungsten tool and citric acid electrolyte through EMM process. An EMM device fabricated for experimentation purpose with pulse generator was utilized in this research. The operating factors preferred for study are voltage, current, pulse-on-time & electrolyte concentration. Taguchi’s L9 design for trials and Grey Relational Analysis (GRA) for multi response optimization were employed. The optimum set of parameters obtained through GRA included 12 V,1.2 A, 15 ms of pulse-on-time period and 20 g/l of solution concentration. The most influential factor observed was pulse-on-time. Though machining was slow with citric acid as electrolyte, holes produced were of good accuracy.
Smart manufacturing is utmost need of industries to secure high productivity and profit. Industry 4.0 encompasses digital transformation of manufacturing industries and service industries. Smart manufacturing can be adopted by not only the large-scale manufacturers, but also small manufacturing enterprises (SME). The implementation of digital system onto each entity or stack holder of the enterprise will help the organization to avoid wastages. This article highlights the issue of wastes in manufacturing, importance of smart machining and proposes a technical approach to reduce such wastages, clearing the way to achieve sustainable manufacturing.
This book shows how Industry 4.0 is a strategic approach for integrating advanced control systems with Internet technology enabling communication between people, products and complex systems. It includes processes such as machining features, machining knowledge, execution control, operation planning, machine tool selection and cutting tool. This book focuses on different articles related to advanced technologies, and their integration to foster Industry 4.0, being useful for researchers as well as industrialists to refer and utilize the information in production control.
Modern engineering applications require the amalgamation of unlike materials for achieving specific thermal, electrical, and physical properties. Aluminium alloys are quite often employ fusion or solid-state processes to join with copper. However, fusion welding of dissimilar materials results in defects such as porosity and the formation of brittle particles. Friction Stir Welding (FSW) is energy efficient, environment friendly process used for joining dissimilar metals. Hence, an attempt is made to join aluminium alloy (AA6061-T6) and pure copper. In this article, the effect of tool pin offset, eccentric weave tool path, and the addition of graphene nano-platelets was studied and compared with the conventional FSW. The effect of pin offset compared to the conventional pin position helped in obtaining a good weld strength due to the large volume of material transportation of base materials and better stirring effect. The novel eccentric weave motion of the tool was useful for obtaining enhanced joint property due to higher holding time, adequate heat input, and uniform mixing during the joining process. A back propagation network (BPN) was utilized in arriving at the optimal process parameters.
Complicated plastic deformation and welding temperature were generated in the nugget zone (NZ) of friction stir welding (FSW) joints leading to different regions being developed, such as shoulder influence zone (SIZ), pin influence zone (PIZ) and swirl zone (SZ). To find the effect of rotation speed on microstructure evolution and mechanical properties of these regions during friction stir welding, serials of AA2195-T8 plates with 7.5 mm thickness were fabricated using different rotation speeds (500, 700 and 900 rpm) and a constant welding speed (50 mm/min). Microstructural characterization was conducted out using electron back scattered diffraction (EBSD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XRD) technologies. Mechanical properties were measured by micro-hardness and tensile test. The results show that grains in the SIZ were mainly shown in wedge-shaped structure and had the high density of low angle boundaries (LABs) showing dominant (100) orientation. However, in the PIZ and SZ, fine and equiaxed grains with dominant (111,101) orientation were observed. With rotation speed increasing, the fraction of LABs increased in the SIZ but showed little changes in the PIZ and SZ. After welding, a large number of T1 and θ′ precipitates almost be completely dissolved in the NZ with many fine δ′/β′ being re-precipitated. It is notable that a few T1 precipitates were observed in the SIZ at a higher rotation speed (900 rpm), which were re-precipitated from the Al matrix after dissolution. In the SIZ, the dominant contribution to yield strength was dislocation strengthening which enhanced with rotation speed increasing. However, in the PIZ and SZ, grain refinement strengthening was the primary strength mechanism, which decreased with rotation speed increasing.
Tailored blanks characterized by variable thickness were friction stir welded (FSWed) with the aim to obtain constant joint properties along the weld seam, regardless of the thickness change. To pursue this goal, the heat input was kept constant by in-process control of tool rotation. A dedicated numerical model of the process was used to determine the tool rotation values as a function of the sheet thickness. The mechanical properties and the microstructure of the FSWed joints, produced with varying process parameters, were studied. It was found that the proposed approach can produce joints with uniform properties along the weld line in terms of stress–strain curve shape, joint strength, elongation at failure, and microstructure.
In the present study, the feasibility of joining 2 mm thick plates of AA5754-H114 to mild steel was examined. Sound friction stir dissimilar butt welding was achieved between thin plates of the automotive grade 5754 aluminum alloy and mild steel for the first time. Moderate rotational speed and a rather slow traverse speed were used. The mechanical properties of the weld were close to the equivalent of the aluminum base metal and a rise in the microhardness of the weld nugget of around 40% compared to the equivalent of the mild steel base metal was presented. An interdiffusion layer with a width of around 5 μm was created at the interface of the two alloys, the extended width of which probably affects positively the mechanical properties of the welds.
Zigzag line is a common defect in friction stir welding (FSW) joint. The formation mechanism of the zigzag line in Al–Cu alloy FSW joint and its influence on the microstructure and mechanical properties during post weld heat treatment (PWHT) were studied by scanning electron microscopy (SEM), microhardness and tensile tests. It is found that the occurrence of zigzag line for PWHT joint is determined by PWHT process which in nature depends on residual stress and thermal stress of FSW joint. The optimization of PWHT process to reduce the residual and thermal stress can trigger for the deterioration of mechanical properties of PWHT joints with zigzag line. No obvious decrease of tensile properties is observed for T6-450 and T6-495 joints although zigzag line appears in the weld. PWHT determines the sizes of zigzag line cracks and consequently determines the fracture location and characteristics of FSW joint.
With the appropriate process parameters, both large and small tools can produce sound joints with tensile strengths (TS) 80% higher than those fabricated with Al base metal. As a large tool moves into the steel, it can peel off and embed steel fragments into the Al matrix, causing critical defects around the embedded fragments. Using small tools and lower rotational speed (RS) will significantly reduce the welding heat, resulting in an unwelded Al/steel interface at the bottom of the weld. Since the tool size and process parameters determine the amount of generated heat, they also determine the thickness of the intermetallic compound (IMC) layer that forms at the Al/steel interface. The welding forces in the weld plane are primarily affected by the tool offset.
Friction stir welding (FSW), a highly efficient solid-state joining technique, has been termed as “green” technology due to its energy efficiency and environment friendliness. It is an enabling technology for joining metallic materials, in particular lightweight high-strength aluminum and magnesium alloys which were classified as unweldable by traditional fusion welding. It is thus considered to be the most significant development in the area of material joining over the past two decades. Friction stir processing (FSP) was later developed based on the basic principles of FSW. FSP has been proven to be an effective and versatile metal-working technique for modifying and fabricating metallic materials. FSW/FSP of aluminum alloys has prompted considerable scientific and technological interest since it has a potential for revolutionizing the manufacturing process in the aerospace, defense, marine, automotive, and railway industries. To promote widespread applications of FSW/FSP technology and ensure the structural integrity, safety and durability of the FSW/FSP components, it is essential to optimize the process parameters, and to evaluate thoroughly the microstructural changes and mechanical properties of the welded/processed samples. This review article is thus aimed at summarizing recent advances in the microstructural evolution and mechanical properties of FSW/FSP aluminum alloys. Particular attention is paid to recrystallization mechanism, grain boundary characteristics, phase transformation, texture evolution, characteristic microstructures, and the effect of these factors on the hardness, tensile and fatigue properties as well as superplastic behavior of FSW/FSP aluminum alloys.
We report that twin-roll cast and subsequently heat-treated Mg–6Zn–1Mn–1Al alloy sheets with a thin thickness of 1 mm were successfully joined by surface-friction welding process. The welded sheet revealed several distinct weld zones, which are closely related to plastic flow and frictional heat generation during welding. Although large microstructural differences were found among the welded zones, the presence of thermally stable Al8Mn5 particles pre-existing in the sheet appeared uninfluenced by the welding process. The role of the microstructural changes induced by the welding process in the hardness variation and tensile properties of the welded sheet is discussed.
In this work, thermo-mechanical behavior and microstructural evolution in similar and dissimilar friction stir welding of AA6061-T6 and AA5086-O have been investigated. Firstly, the thermo-mechanical behaviors of materials during similar and dissimilar FSW operations have been predicted using three-dimensional finite element software, ABAQUS, then, the mechanical properties and the developed microstructures within the welded samples have been studied with the aid of experimental observations and model predictions. It is found that different strengthening mechanisms in AA5086 and AA6061 result in complex behaviors in hardness of the welded cross section where the hardness variation in similar AA5086-O joints mainly depends on recrystallization and generation of fine grains in weld nugget, however, the hardness variations in the weld zone of AA6061/AA6061 and AA6061/AA5086 joints are affected by subsequent aging phenomenon. Also, both experimental and predicted data illustrate that the peak temperature in FSW of AA6061/AA6061 is the highest compared to the other joints employing the same welding parameters.
The present investigation is aimed at evaluating the influence of tool rotation rate and welding speed on the microstructure, tensile properties, and fracture mode of 6061 A1-T651 alloy after friction stir welding (FSW). TEM results revealed that in the nugget zone (NZ), FSW resulted in the dissolution of fine needle-shaped precipitates that previously existed in the base metal. At a given rotation rate of 1400rpm, the yield strength (YS) and ultimate tensile strength (UTS) of the welded joints increased with increasing welding speed from 200 to 600mm/min. However, the UTS of the joints was nearly independent of the rotation rate. Furthermore, the relationship between the hardness distribution and fracture location has also been identified.
The heating distribution assessment on similar and dissimilar friction stir welded joints in AA6082 and AA5754 aluminium alloy sheets was investigated. The FSW experiments were carried out using constant rotational and welding speeds of 1500 rpm and 60 mm/min, respectively. Temperature was locally measured by means of K-type thermocouples inserted into thin grooves located on the bottom side of the sheets, in fixed positions, very close to the welding line. It was observed that the mechanical properties of joints are related to the heat distribution. In order to obtain a completely non intrusive temperature monitoring, that was able to follow the process dynamic, a non-contact measurement system based on infrared thermography was also developed. Such system, used for the experimental evaluation of temperature on the upper surface of the joints, is also able to detect the presence of flow defects with a non-destructive method, demonstrating its effectiveness as a diagnostic instrument for the on-line quality control of welded joints.
Grain refinement in an as-cast 0.16%Zr modified 7475 aluminum alloy was studied by means of compression at 490 °C and metallographic observations. The σ versus ε behavior shows a significant strain softening just after yielding and an apparent steady-state flow at strains of above 0.3. The structural changes are mainly characterized by development of deformation bands at an early stage of deformation (ε≤0.3), followed by new grain evolution during steady-state flow due to operation of grain boundary sliding (GBS). GBS can result in local lattice rotation and formation of deformation bands in the as-cast coarse grain interiors. The number and the misorientation angle of deformation bands increase with deformation, followed by evolution of new grains in high strain. It is concluded that grain refinement occurs by a deformation-induced continuous reaction; that is continuous dynamic recrystallization (CDRX). A key role of GBS and second phase dispersoids on CDRX is discussed in detail.
The Portevin-Le Chatelier (PLC) effect is a manifestation of macroscopic scale non-uniformities which have their origins on a microstructural level. The coordination of dislocation level events within grains, across grain boundaries, and eventually on to the level of a test specimen or workpiece make the PLC effect subject to a large range of variables. An holistic approach which examines the effect across this spectrum of variables potentially allows for a clearer overview of the phenomenon. This review covers experimental work which deals with a full range of the variables. Aspects discussed include manifestations of dynamic strain aging, the occurrence or not of one or more critical strains, the formation of deformation bands, and the effects of specimen geometry. In addition, an examination of the influence of microstructural variables including the solute concentration, grain size, and accumulated prior strain are presented. Dynamic strain aging related phenomena continue to receive regular attention in the literature and theoretical modelling has been developed to the point where qualitative agreement exists with specific aspects such as the critical strains. Modelling of the effect is, however, beyond the scope of this review.
Dissimilar friction stir welding (FSW) of heat (AA 6082-T6) and non-heat (AA 5754-H22) treatable aluminium alloys, in lap joint configuration, was performed in this work. The base material plates were 1 mm thick. Welds were performed combining different plates positioning, relative to the tool shoulder, in order to assess the influence of base materials properties on welds strength. Three different tools were tested, one cylindrical and two conical, with different taper angles. Welds strength was characterized by performing transverse and tensile-shear tests. Strain data acquisition by Digital Image Correlation (DIC) was used to determine local weld properties. The results obtained enabled to conclude that the dissimilar welds strength is strongly dependent on the presence of the well-known hooking defect and that the hooking characteristics are strongly conditioned by base materials properties/positioning. By placing the AA 6082-T6 alloy, as top plate, in contact with the tool shoulder, superior weld properties are achieved independently of the tool geometry. It is also concluded that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the most suitable solution for the production of welds with similar advancing and retreating sides strengths.
An attempt has been made to study the tailor welded blanks (TWBs) made by friction stir welding (FSW) with five different tool pin profiles. The formability of welded blanks was evaluated at constant FSW process parameters. It has been found that the welded blanks with square pin profile tool produced better formability properties as compared to other tool pin profiles. It was found that the pulsating action of the square pin profile is said to be the reason for this improvement. A microstructural evaluation performed on the blanks revealed that the stir zone created by taper cylindrical and stepped cylindrical tools was less homogeneous than that of the square tool, resulting in less formability. The limiting dome height (LDH) of square pin profile tool was found to be 14 mm while those of taper cylindrical and stepped cylindrical tools are 12.5 mm and 12.4 mm, respectively.
The microtextures in a friction-stir-welded magnesium (Mg) alloy, AZ61, with a nugget-shaped stir zone were analyzed by orientation imaging microscopy (OIM). The base material had a (0002) texture ((0002) parallel to the sheet plane, parallel to the welding direction). Friction stir welding produced texture components different from those of the base material in the stir zone. Except for the upper surface of the plate, most of the stir zone had a texture with a strong tendency for the (0002) basal plane to align with the surface of the hard pin of the welding tool. Formation of this texture component was attributable to shear deformation arising from the rotation of the hard pin. The (0002) planes tended to align with an ellipsoidal surface in the nugget-shaped stir zone. The present study suggests that the nugget shape, which is a characteristic feature of the stir zone, is strongly related to formation of the ellipsoidal surface described by the (0002) basal plane.
The influence of pin geometry and process parameters on the morphology and strength of friction stirlap welds, in very thin sheets, is analysed. The base material is the AA5754-H22 work hardened alu-minium alloy. Three different pin geometries were tested, one cylindrical and two conical, with differenttaper angles. For each pin geometry, varying welding speeds, ranging from 350 to 1000 mm/min, weretested in order to simultaneously weld properties and process productivity. Weld defects assessment wasperformed using metallographic analyses. strength was by performing mechanical tests both monotonicand cyclic loading conditions. Monotonic tests included performing transverse and lap tensile-shear tests.Strain data acquisition using Digital Image Correlation (DIC) enabled to determine local weld propertiesas the joints failure mode monotonic loading. The results show that the use of unthreaded conical pintools, with a low shoulder/pin diameter relation, is the more suitable solution for the production of goodquality welds. Irrespective of the pin geometry, very high joint strength efficiencies (close to 90%) wereobtained when loading the retreating side of the welds. It is also shown that good quality welds may beproduced at very high welding speeds.
The influence of pin geometry and process parameters on the morphology and strength of friction stir lap welds, in very thin sheets, is analysed. The base material is the AA5754-H22 work hardened aluminium alloy. Three different pin geometries were tested, one cylindrical and two conical, with different taper angles. For each pin geometry, varying welding speeds, ranging from 350 to 1000 mm/min, were tested in order to simultaneously weld properties and process productivity. Weld defects assessment was performed using metallographic analyses. strength was by performing mechanical tests both monotonic and cyclic loading conditions. Monotonic tests included performing transverse and lap tensile-shear tests. Strain data acquisition using Digital Image Correlation (DIC) enabled to determine local weld properties as the joints failure mode monotonic loading. The results show that the use of unthreaded conical pin tools, with a low shoulder/pin diameter relation, is the more suitable solution for the production of good quality welds. Irrespective of the pin geometry, very high joint strength efficiencies (close to 90%) were obtained when loading the retreating side of the welds. It is also shown that good quality welds may be produced at very high welding speeds.
The effect of process parameters, tool geometry and size on friction stir welding of thin sheets in AZ31 magnesium alloy was widely investigated. In particular, two properly designed tools, with different values of the shoulder diameter, were used; each of them was manufactured both in the "pin" and "pinless" tool configurations. It was shown that at the lowest shoulder diameter investigated (8 mm), the pin tool configuration leads to the obtaining of ultimate tensile strength and ductility values higher than those provided by the "pinless" one. By increasing the shoulder diameter (19 mm), a strong beneficial effect on both ductility and strength of the joint is obtained even though the welding performed using the "pin" tool configuration is critically affected by the process parameters. An investigation has been also carried out in order to evaluate the micro-hardness and microstructure covering all regions of the welded joints. A different metal flow can be clearly observed depending on the presence/absence of pin. Finally, a more homogeneous microstructure is obtained using the "pinless" tool configuration.
In the stirred zone of friction-stir welds of an aluminum alloy 6N01 plate (formed through extrusion), a zigzag bond line was observed after etching by an aqueous solution of 10% NaOH, when the revolution pitch (tool traveling speed/rotation rate) was greater than a critical value. SEM and TEM observations revealed that the bond line consisted mainly of particular inclusions 0.01-0.2μm in size. The inclusion was identified as complex oxide involving Al, Mg, and Si based on EDX analyses. The inclusion can be considered to originate from the oxide film that was formed on the plate surface during the extrusion process, since its amount was reduced significantly by removing the as-extruded surface layer through mechanical cutting or grinding. The presence of the bond line had no significant influence on the tensile strength or fatigue strength of the joint, since it was fractured in the heat-affected zone in the tensile and fatigue tests.
The occurrence and nature
of “kissing bonds” have been studied in
three solid-state welding processes: friction
stir welding, extrusion charge welding,
and extrusion seam welding. A kissing
bond is the descriptive term for two surfaces
lying extremely close together, but
not close enough for the majority of the
original surface asperities to have deformed
sufficiently in contact for atomic
bonds to be created. Depending on their
location and extent, they may have detrimental
effects on the fatigue life and
through-thickness load-bearing capacity
of the component.
This paper presents analogies between
kissing bonds in the above-mentioned
joining methods using fractographic evidence
and phenomenological hypotheses.
The effects of these discontinuities on the
mechanical properties of these joints produced
in 6xxx-Series aluminum alloys used
in automotive and marine structural applications
are discussed.
a b s t r a c t 6063-T4 aluminium alloy sheets of 3 and 6 mm thicknesses were friction stir butt welded using a square tool pin at a wide range of tool rotational speeds. Properties of obtained welds were characterised using tensile tests, optical micrographs, X-ray diffraction, and transmission electron microscopy. Shape, size, and distribution of precipitates in weld zones, and strength and ductility of welds were seen to directly correlate with peak temperatures in weld nugget and heat affected zones, independent of sheet thickness. In addition, fluctuations in measured temperature profiles, for 3 mm sheets, were seen to correlate with an increase in scatter of weld nugget zone properties for 3 mm sheets. Optimal weld strength and duc-tility were obtained for peak weld nugget zone temperatures of around 450 °C and corresponding peak heat affected zone temperatures of around 360–380 °C. Results obtained suggest that, at least for natu-rally aged aluminium alloys, nature of temperature evolution and magnitudes of peak temperatures in weld nugget and heat affected zones provide information on uniformity of properties in weld zones, over-aging of heat affected zones, and formation of tunnel defects from improper material mixing at low weld zone temperatures.
AA5754/AA7075 was butt-welded by friction stir welding, and the joint of each weld case was identified by ultimate tensile strength, percentage of elongation, and hardness. Moreover, the significance of each parameter was investigated, and a mathematical relation was constructed by regression analysis. A defect-free joint was achieved in the case of a weld produced with 1000 rpm of tool rotational speed, 80 mm/min of welding speed, and an 22-mm tool shoulder diameter. Most of the failures are located at the bottom of the pin and side of AA7075. The ultimate tensile strength (UTS) decreases with increasing welding speed (WS) or increasing tool rotational speed (TRS). Hardness distribution in the weld zones varied dependent on the nugget zone formation affected by TRS and WS. The present study also investigated the significance and contribution of each parameter on the UTS by analysis of variance (ANOVA). From the results of ANOVA, the conclusion reached is that the all the parameters have a great influence on UTS. The contributions are 41.41 % for WS, 17.58 % for diameter, and 13.28 % for TRS. Moreover, a full quadratic model was constructed between the parameters and the UTS value. The results show that the variation from the predicted values was between 0.41 % and 10.36 %. The strength of the model was analyzed by R-Sq. The achieved R-Sq is 0.892, which means that there is a strong relation between predicted and actual values.
Friction stir welding (FSW) process is a promising solid-state joining process with the potential to join low-melting point material, particularly, aluminium alloy. The most attractive reason for joining aluminium alloy with this process is the avoidance of the solidification defects formed by conventional fusion welding processes. In this article, an attempt has been made to develop an empirical relationship between FSW variables and tensile strength. Central composite rotatable design was used by considering four factor and five levels, which enables to quantify the direct and interactive effect of four numeric factors, that is, tool rotational speed, welding speed, axial force, and tapered pin diameter on the tensile strength. The developed relationship is useful for prediction of tensile strength in friction stir welded AA6082 aluminium alloy joints at 95% confidence level. It will also be helpful for selection of process variable to obtain desired strength of the joint. Furthermore, the optimized capabilities in design-expert software were used to numerically optimize the input parameters. At the optimal parameters, three experiments were conducted to compare the predicted value of tensile strength with the experimental value.
Tailor welded blanks (TWB) in Al alloys are an attractive structural solution for application in the shipbuilding sector, mainly due to reductions in weight and lower production costs. In the present study, the global and local mechanical properties of dissimilar friction stir welded TWB were assessed. The joints were manufactured with dissimilar Al–Mg alloys and thicknesses (6 and 8 mm) of particular interest to the shipbuilding sector (AA5083 and AA5059). A digital image correlation system (DIC) linked to a tensile test system was used to characterise the local strain fields, and true stress–strain curves were generated for several TWB sub-zones. Microhardness and DIC analyses showed that the stir zone of the TWB presented overmatching in relation to the weakest base material, and that the joints displayed excellent overall mechanical performance that was comparable to the AA5059 base material in terms of strength and ductility. The fatigue strength was evaluated by means of tension–tension fatigue tests, and the TWB joints reached the fatigue keen with a stress range of 70 MPa.
In the present study, the effect of tool pin profile on microstructure and mechanical properties of friction stir welded pure copper joints were investigated. Two different tools with threaded cylindrical and square pin profiles were used to fabricate the joints at constant rotation rate of 600 rpm and traverse speed of 75 mm/min. Four K-type thermocouples were used to record the temperature histories of samples during FSW. Microstructure features of the joints were characterized by optical microscopy and the obtained images were quantified using image analysis technique. Tension test and Vickers hardness measurements were also performed to characterize the mechanical properties of the joints. Obtained results showed that sample welded using square pin profile had finer recrystallized grain structure and higher mechanical properties relative to sample welded by threaded cylindrical one. These results were attributed to higher eccentricity of the square pin profile and its pulsation effect which led to higher degree of plastic deformation and higher heat input into the joints.
The microstructure evolutions of severely deformed aluminum sheets by Constrained Groove Pressing (CGP) after Friction Stir Welding (FSW) are investigated. To do so, the specimens are deformed in three different strains using CGP process which make different the initial microstructures. Then, the specimens are joined at various revolution pitches (traveling speed/rotation speed ratio) of 0.20, 0.25 and 0.33 mm/r. To understand the effect of initial strains on the properties of joints, the microhardness measurements and microstructure investigations of different areas from retreating to advancing sides of the joints are carried out. The results achieved from FSW of CGPed samples are compared with those achieved from FSW of as-annealed ones (0 pass). It is found that in contrast to 2 passes CGPed specimens, for specimens strained by 1 pass of CGP process after FSW at low revolution pitch, the grain size at the center of stir zone is finer than that at around of stir zone center. Also, it is revealed that for CGPed samples in contrast to as-annealed ones, some recrystallized grains are formed in HAZ. Moreover, the amount of recrystallized grains in HAZ is different at advancing and retreating sides.
To improve the plasticity of friction stir welded joints for plastic processing applications, post-weld heat treatment (PWHT) of 2024-O aluminum alloy friction stir welding joints was carried out at annealing temperatures from 250°C to 450°C with an interval of 50°C for 2h, followed by cooling to 200°C in the furnace. The effect of PWHT on the microstructure and plastic deformation behavior of the joints was investigated. It was found that the fine-equiaxed grains are stable and retained in the nugget of the joints even after annealing at 450°C for 2h. However, the grains in the thermo-mechanically affected zone (TMAZ) of the joints become coarse and equiaxed as annealing temperature increases. The plastic deformation of as-welded joint is very heterogeneous. In contrast, the plastic deformation of PWHT joint is relatively homogeneous by both the nugget and the base material showing large deformation. The decrease in elongation of as-welded joints is completely recovered by PWHT. The high ductility of the joint is mainly attributed to the retention of the fine-equiaxed grains in the nugget during PWHT.
A new experimental procedure—stir-in-plate welding was adopted to eliminate the initial butt surface of two plates to be joined and examine the effect of the initial butt surface on the formation of the zigzag line and the tensile properties of the welds. The comparison between the butt and stir-in-plate welds indicated that under as-welded condition the zigzag line did not show up in the welds, and two welds exhibited similar tensile properties and fracture characteristics. After post-weld T6-treatment, the zigzag line appeared on the butt weld as zigzag micro-crack at the root tip and discontinuously-distributed cavities of 50–200μm throughout the weld, which were verified to be associated with the oxide particles. This resulted in the reduced tensile strength and significantly deteriorated ductility with the fracture initiating and propagating along the zigzag line. No zigzag line was discernible on the T6-treated stir-in-plate weld.
Onion rings are the most prominent features of most friction stir welds. The origin and the effect of these on properties are not clearly understood. In this paper, an attempt has been made to explain the formation of onion rings. The formation of onion ring is found to be a geometric effect due to the fact that cylindrical sheets of material are extruded during each rotation of the tool and the cutting through the section of the material produces an apparent ‘Onion Rings’. It is postulated that the tool appears to wait for a very short time to produce frictional heat and extrude a cylindrical shaped material around to the retreating side of the joint. The spacing of the markings has been found to be equal to the forward motion of the tool in one rotation.
The microstructural evolution during polyslip in fcc metals is investigated by the examples of Al, Ni, Ni-Co alloys and an Al-Mg alloy, deformed at room temperature either by rolling or by torsion. The principles governing this evolution appear to be the following: (1) There are differences in the number and selection of simultaneously acting slip systems among neighboring volume elements of individual grain. In any one volume element (called a 'cell block'), the number of slip systems falls short of that required for homogeneous (Taylor) deformation, but groups of neighboring cell blocks fulfil the Taylor criterion collectively. (2) The dislocations are trapped into low-energy dislocation structures in which neighbor dislocations mutually screen their stresses. The microstructural evolution at small strains progresses by the subdivision of grains into cell blocks delineated by dislocation boundaries. These boundaries accommodate the lattice misorientations, which result from glide on different slip system combinations in neighboring cell blocks. The cell blocks are subdivided into ordinary cells and both cell blocks and cells shrink with increasing strain. All observations appear to be in good accord with the theoretical interpretation.
The present investigation presents a composite picture of the microstructural developments in a friction stir welded (FSW) AA5052. Optimized, defect free and chemically homogeneous, FS weld was generalized in four regions – base material (BM), nugget, advancing side (AS) and retreating side (RS), using standard nomenclatures. Each region had its signature of microstructural features. AS had clear indications of shear and of grain fragmentation. The nugget region, on the other hand, had nearly equiaxed grains, with strong in-grain misorientation and presence of grain-interior dislocation structure ruling out contributions from static recrystallization. Equiaxed grains of the nugget region had typical onion ring structure – each ring did approximately correspond to one dominant family of orientation. Microstructural developments, as obtained from relative grain refinement, in-grain misorientation development, relative banding, etc., were most significant in nugget followed by AS and then by RS. Heterogeneous plastic deformation and thermal activation through localized heating/friction were the apparent causes. Most of the friction stir welded specimen fractured away from the nugget and showed ductile mode of failure.
The Luders band propagation in fine grained Al-6% Ni and Al-6% Ni-0.3 Mg is found to be very stress sensitive. The band velocity VL is related to the stress via VL = B0(σ)m1 with m1 = 100–220. The Luders strain is independent of band velocity and inversely dependent on grain size. The assumption that the free slip distance during Ludering is approximately equal to the grain size is consistent with the experimental results.RésuméLa propagation des bandes de Lüders dans des alliages Al-6% dans des alliagesAl-6% Ni et Al-6% Ni-0,3% Mg, à grain fin est très sensible à la contrainte. La vitesse des bandes de Lüders VL est liée à la contrainte par la relation VL = B0(σ)m1, où m1 est compris entre 100 et 220. La déformation de Lüders est indépendante de la vitesse des bandes et elle varie en sens inverse de la taille des grains. Nos résultats expérimentaux s'accordent avec l'hypothèse selon laquelle la distance de glissement libre au cours du phénomène de Lüders est à peu près égale à la taille des grains.ZusammenfassungDie Lüdersbandausbreitung in feinkristallinem Al-6% Ni und Al-6% Ni-0,3 Mg ergibt sich als sehr spannungsempfindlich. Die Bandgeschwindigkeit VL hängt mit der Spannung über VL = B0(σ)m1 zusammen, m1 = 100 bis 200. Die Lüdersdehnung ist unabhängig von der Bandgeschwindigkeit und hängt invers von der Korngröβe ab. Die Annahme, daβ der freie Gleitweg während des Lüdersprozesses ungefähr so groβ ist wie die Korngröβe, ist konsistent mit den experimentellen Ergebnissen.
Over the past decade, friction stir welding (FSW) has rapidly become an important industrial joining process, particularly in the aluminum industry. Included among the advantages of FSW are such important attributes as improved weld strength and the elimination of cracking and porosity. During the friction stir process, the metal undergoes a tortuous deformation path that is not yet fully understood. The crystallographic texture that evolves during FSW contains sharp spatial gradients that undoubtedly influence the integrity of the weld and surrounding region in subsequent performance. The locally measured textures are discussed in the context of the material flow required to produce such textures, ultimately resulting in an estimate of the flow field present during FSW.
The Portevin-Le Chatelier (PLC) effect is a manifestation of macroscopic scale non-uniformities which have their origins on a microstructural level. The coordination of dislocation level events within grains, across grain boundaries, and eventually on to the level of a test specimen or workpiece make the PLC effect subject to a large range of variables. An holistic approach which examines the effect across this spectrum of variables potentially allows for a clearer overview of the phenomenon. This review covers experimental work which deals with a full range of the variables. Aspects discussed include manifestations of dynamic strain aging, the occurrence or not of one or more critical strains, the formation of deformation bands, and the effects of specimen geometry. In addition, an examination of the influence of microstructural variables including the solute concentration, grain size, and accumulated prior strain are presented. Dynamic strain aging related phenomena continue to receive regular attention in the literature and theoretical modelling has been developed to the point where qualitative agreement exists with specific aspects such as the critical strains. Modelling of the effect is, however, beyond the scope of this review.
In this study, Al-5083 and St-12 alloy sheets were friction stir lap welded at different travel (7‐23 cm min−1) and rotation (750‐1125 rev min−1) speeds of the welding tool. The welded joints were characterised by various methods including shear tensile and Vickers microhardness tests, optical and scanning electron microscopies and X-ray diffraction analysis. The results showed that the weld zone defects decreased, and the joint strength also improved significantly with the reducing tool travel speed from 23 to 7 cm min−1. The travel speed of 11 cm min−1 was an optimum speed within the travel speeds investigated in this work. Additionally, raising the tool rotation speed enhanced the joint strength slightly. The microhardness results confirmed the formation of intermetallic phase layer with the hardness of ∼335 HV at the swirl layered structure.
In order to characterize plastic flow during friction-stir welding, the microtextures in a friction-stir weld of the precipitation-hardened aluminum alloy 6063 have been analyzed by orientation imaging microscopy (OIM). The base-material plate has a Goss orientation. The weld center region, except for the upper surface, takes a typical shear texture component with two types of orientations. The orientations have a pair of common {111} and 〈110〉 parallel to the cylindrical pin surface and transverse direction of the plate, respectively. The typical texture component is also observed around the weld center on the midsection, although it rotates about the plate normal direction. A microtexture analysis after postweld heat treatment has suggested that dynamic recrystallization during friction-stir welding generates the recrystallized grains at the weld center.
Material flow in friction stir welds has been visualised using embedded marker materials. The fidelity of the visualisation technique has also been demonstrated. Results from the flow visualisation show that the friction stir welding process can be roughly described as an in situ extrusion process wherein the tool shoulder, the weld backing plate, and the cold base metal outside the weld zone form an ‘extrusion chamber’ which moves relative to the workpiece. Deviation from this description occurs primarily at the top surface of the weld where significant material transport occurs owing to the action of the rotating tool shoulder. The transport caused by the shoulder leads to a small amount of circulation about the longitudinal axis of the weld with material moving primarily from trailing to leading sides at the top of the weld and primarily from leading to trailing near the middle and bottom of the weld.
The effect of welding parameters and tool configuration on the surface appearance, mechanical and microstructural properties of similar and dissimilar FSWed joints in AA5754 and AZ31 thin sheets was widely investigated. Two different tool configurations, with and without the pin, were used. As far as the similar friction stir welded joints in AZ31 and in AA5754 alloys are concerned, it was shown that the “pinless” tool leads to the obtaining of higher values of the tensile strength and ductility as compared to the “pin” one. On the contrary, by considering the dissimilar friction stir welding between AZ31 and AA5754 thin sheets, the welding process becomes very critical as the “pinless” tool is used. Sound dissimilar joints were obtained using the “pin” tool configuration, even though the effect of the material position with respect to the welding tool is a very important factor to be considered. A marked improvement in the surface appearance and mechanical properties was obtained by placing aluminium alloy in the advancing side and magnesium alloy in the retreating one. An investigation has been also carried out in order to evaluate the microstructural properties of similar and dissimilar welded joints.
Hot deformation of Al to high strains where the elongated grain thickness is reduced to near the subgrain diameter gives rise to equiaxed crystallites each having several facets of high misorientation. A model of continuous dynamic recrystallization, based on strain induced boundaries continuously incorporating dislocations, has many inconsistencies including the mistaken claim that dynamic recovery could not maintain low angle subboundaries. Such crystallites can be explained by change in grain geometry combined with dynamic recovery that also maintains steady state.
The microstructural evolution during polyslip in f.c.c. metals is investigated by the examples of Al, Ni, Ni-Co alloys and an Al-Mg alloy, deformed at room temperature either by rolling or by torsion. The principles governing this evolution appears to be the following: (a) There are differences in the number and selection of simultaneously acting slip systems among neighboring volume elements of individual grains. In any one volume element (called a cell block), the number of slip systems falls short of that required for homogeneous (Taylor) deformation, but groups of neighboring cell blocks fulfil the Taylor criterion collectively. (b) The dislocations are trapped into low-energy dislocation structures in which neighbor dislocations mutually screen their stresses. The microstructural evolution at small strains progresses by the subdivision of grains into cell blocks delineated by dislocation boundaries. These boundaries accommodate the lattice misorientations, which result from glide on different slip system combinations in neighbouring cell blocks. The cell blocks are subdivided into ordinary cells and both cell blocks and cells shrink with increasing strain. All observations appear to be in good accord with the theoretical interpretation. However, some problems remain to be solved quantitatively.
Friction stir welding (FSW) has received a great deal of attention as a new solid-state welding technique. In the present study, the relationship between the microstructure of stir zone and the mechanical property of FS-welded 5083 aluminum alloy was investigated. The microstructures of the stir zones consisted of fine equiaxed grains at various FSW conditions in FS-welded 5083 Al alloy. However, the grain size of the stir zone decreased with the decrease in friction heat flow during FSW. The ductility in FS-welded 5083 Al alloy increased with the decrease in friction heat flow. It was indicated that the formability in FS-welded 5083 Al alloy was improved by the refinement of grain size of the stir zone.
The deformation and fracture of Al-Mg alloys have been investigated over a range of strain rates and temperatures. The rate
and temperature-dependence of the deformation can be understood on the basis of the mobility of Mg atoms. When the Mg atoms
can diffuse at a sufficient rate they interact with dislocations to produce serrated yielding and a zero or negative strain
rate sensitivity. This greatly restricts the tensile ductility. Outside of this serrated flow regime enhanced ductilities
are achieved due to the positive strain rate sensitivity stabilizing any inhomogeneities which develop. However, the final
fracture is also influenced by the constituent particle concentration. Voiding occurs at particles and if the concentration
of particles is sufficiently large the voids link up by local shear. Decreasing the constituent particle concentration, together
with a reduction in the amplitude of serrations, results in larger tensile ductilities. At high temperatures, quite large
strain rate sensitivities can be achieved but the ductility is finally limited by the propensity for voiding in these alloys.
Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered
essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while
introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties
both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure,
a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically
affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point
and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure
that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased,
while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced
tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused
localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength.
Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable
potential for welding 7075 T651 aluminum.
The external factors on the friction stir welding defects are so abundant that the experiments of friction stir welding were conducted for 5456 aluminum alloy. With the changes of the tool tilt angle and material condition, defects can be generated. These defects can be conventional ones (lack of penetration or voids), or lazy S, which are unique to friction stir welding. However, the origin of the defects remains an area of uncertainty. In this study, an attempt has been made to investigate the formation of these defects. The typical welding defects of friction stir welding joint for 5456 aluminum alloy were analyzed and discussed, respectively, by using optical microscopy (OM), energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscope (SEM). The microscopic examination of the nugget zone and fracture location of the weld confirms that the tilt angle can change the plastic material flow patterns in the stir zone and accordingly control the weld properties. In addition, the oxide layer from the initial butt surface during FSW is dispersed at the grain boundary. These A12O3 particles are actually the major cause of failure of the joint.
In the paper a numerical model aimed to the determination of the average grain size due to continuous dynamic recrystallization phenomena (CDRX) in friction stir welding processes of AA6082 T6 aluminum alloys is presented. In particular, the utilized model takes into account the local effects of strain, strain rate and temperature; an inverse identification approach, based on a linear regression procedure, is utilized in order to develop the proper material characterization. (c) 2005 Elsevier Ltd. All rights reserved.
Friction stir welding (FSW) is a solid state welding process for joining aluminum alloys and has been employed in aerospace, rail, automotive and marine industries for joining aluminium, magnesium, zinc and copper alloys. In FSW, the base metal properties such as yield strength, ductility and hardness control the plastic flow of the material under the action of rotating non-consumable tool. The FSW process parameters such as tool rotational speed, welding speed, axial force, etc. play a major role in deciding the weld quality. In this investigation, an attempt has been made to establish relationship between the base material properties and FSW process parameters. FSW joints have been made using five different grades of aluminium alloys (AA1050, AA6061, AA2024, AA7039 and AA7075) using different combinations of process parameters. Macrostructural analysis has been done to check the weld quality (defective or defect free). Empirical relationships have been established between base metal properties and tool rotational speed and welding speed, respectively. The developed empirical relationships can be effectively used to predict the FSW process parameters to fabricate defect free welds.
In this paper, the salient intricacies of friction stir welding of aluminum alloy 2024 are highlighted. Influence of welding parameter, primarily the heat flow conduction path, on microstructural development of a 0.125 in (3 mm) thick plate of the aluminum alloy is presented. The conjoint influence of weld parameter and intrinsic microstructural features on tensile deformation and quasi-static fracture behavior is presented and discussed. The tensile properties and fracture behavior of the welded sample is compared with the unwelded counterpart. The microscopic mechanisms governing tensile or quasi-static fracture are rationalized in light of intrinsic microstructural features of the welded sample, deformation characteristics of the alloy microstructure, and nature of loading.
A local region in the preferentially etched line at the root part of a friction stir welded Al alloy was directly observed by TEM. TEM clarified that the preferentially etched line consisted of zigzag region having a high density of amorphous Al2O3 particles which originated from the initial butt surface oxide layer.
The grain structure, dislocation density and second phase particles in various regions including the dynamically recrystallized zone (DXZ), thermo-mechanically affected zone (TMAZ), and heat affected zone (HAZ) of a friction stir weld aluminum alloy 7050-T651 were investigated and compared with the unaffected base metal. The various regions were studied in detail to better understand the microstructural evolution during friction stir welding (FSW). The microstructural development in each region was a strong function of the local thermo-mechanical cycle experienced during welding. Using the combination of structural characteristics observed in each weld region, a new dynamic recrystallization model has been proposed. The precipitation phenomena in different weld regions are also discussed.
Al–Mg–Si alloy plates friction stir welded at a tool traverse speed of 400 mm/min exhibited higher tensile strength with 45° shear fracture, whereas lower tensile strengths with nearly vertical fractures were observed for samples welded at a lower speed of 100 mm/min. The fracture paths corresponded well with the lowest hardness distribution profiles in the joints. The heat indexes cannot be used as parameters to evaluate the thermal input, mechanical properties and fracture mode.
The microstructure and material properties of continuous cast 5052 alloy sheet in as-received condition (as-received sheet) and laboratory cold rolled condition (lab-processed sheet) were investigated after annealing treatment. Microstructural examinations show that the cold rolling process increases the extent of centerline segregation of second-phase particles. The increase in rolling reduction results in a decrease of grain size and a more random distribution of crystallite orientations. Tensile test results indicate that all the sheets exhibit two-stage strain-hardening behavior. Cold rolling increases the total elongation and n2-value in the transverse direction of the lab-processed sheet with a thickness of 1.6 mm. However, further increase in the rolling reduction leads to an increase of UTS with a decrease of elongation and n2-value. Furthermore, from the determined forming limit curves (FLCs), it is found that the 1.6 mm thick lab-processed sheet has better stretchability than the as-received sheet, whereas further cold rolling reduces the level of FLC. The effects of cold rolling on the mechanical property and formability are discussed in terms of the microstructural changes.
Initial oxide layer on the butt surface fragments during friction stir welding (FSW) often remaining as a faint zigzag-line pattern on the cross section. When remnants of the oxide layer often adversely affects the mechanical properties in the weld, it is called as “kissing-bond”. The present study systematically examines the effect of oxide array on the bend property in the root region of friction stir (FS) welded Al alloy 1050 by transmission electron microscopy (TEM) to clarify the identity of “kissing-bond”.
Abnormal grain growth can be a critical issue during the post-processing heat treatment of friction stir welded or processed aluminum alloys. Various theories have been proposed to elucidate the origin of this behavior. This viewpoint paper addresses the issues with reference to the mechanisms involved and their implications for friction stirred microstructures.
This investigation highlights the influence of axial load, and the effect of position of the interface with respect to the tool axis on tensile strength of the friction stir welded joint. The axial load is continuously varied by linearly increasing the interference between the tool shoulder and the surface of the base material. The interface position with respect to the tool axis is continuously changed by keeping the feed direction at an angle to the interface. The base material used in this study is Al–Zn–Mg alloy, 7020-T6, of 4.4 mm thickness. It is found that there is an optimal axial load, above which the weld is defect-free, with joint efficiency of 84%. There is a tolerance for interface position; i.e., the tool can be allowed to deviate away from the interface without deteriorating joint efficiency of the weld. The tool can be allowed to deviate from the interface in either side, but the tolerance is higher when the interface is located in the advancing side of the tool.
The results of experimental activity on friction stir welding (FSW) of aluminum alloys are reported. Butt joints of two different materials, namely AA2024-T4 and AA7075-T6, were investigated from a metallurgical point of view. Grain dimensions and insoluble particle densities were investigated both in the parent materials and in the joints. Furthermore, the effect of post-welding heat treatments on the joint strength was studied.
The microstructure of the stirred zone (SZ) resulting from friction stir processing or welding (FSP/FSW) has usually been assumed to be uniform when discussing the mechanical properties. However, numerous works have indicated that the fine-grained microstructures in the SZ were non-uniform, with precipitate, texture and grain size gradients caused by the severe plastic deformation and heat distribution. In this work commercial aluminum alloy 5083-H112 was subjected to FSP and fine-grained microstructures with an average grain sizes of 2.7–13.4 μm were obtained by controlling the FSP conditions. The stress–strain curves exhibited stepped yield point elongation, which was suggested to be associated with these characteristic non-uniform microstructures. Tensile tests indicated that the Hall–Petch relationship held in this FSP alloy when taking account of the average grain size. Toughness analysis indicated that the optimum toughness was anticipated to be obtained around a grain size of ∼1 μm for this FSP alloy.