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Joint quality of conventional refill friction stir spot welding (RFSSW) is sensitive to welding parameters, and the welding parameters are difficult to control. Thus, deep surface indentation, large hook angle, and void usually occur within the RFSSW joint. An extra-filling RFSSW method is proposed in accordance with defect characteristic. The addi...
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In the present study, lap joints of dissimilar 5052 aluminum alloy and pure copper were fabricated by friction stir spot welding process. The work was aimed to find simultaneous effect of parameters such as tool rotary speed (1000, 1500, and 2000 rpm) and dwell time (5, 10, and 15 s) on lap shear force (LSF), hardness, and microstructure evolution....
In this study, a CALPHAD-coupled finite element model was established to reveal the formation mechanism of hot cracks (including liquation and solidification cracks) in the dissimilar 6061/7075 resistance spot welding joints. The partially melting zone (PMZ) and the fusion zone solidified under tension during the cooling stage. When the composition...
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Friction stir spot welding a relatively new solid-state joining technique usually used by automotive manufacturers as alternative to rivets and conventional spot welding resistance has led to the development of a fairly new technique a double-sided friction stir spot welding technique, this method was implemented for aluminum alloy AA6061-T6 by 2 m...
Citations
... Several researchers reported that the failure of RFSSW joints of aluminum sheets un der tensile shear loads resulted in two typical fracture types: through-the-weld and pul out [31][32][33] fractures. The first one was a shear fracture, in which the nugget remaine ...
... Several researchers reported that the failure of RFSSW joints of aluminum sheets under tensile shear loads resulted in two typical fracture types: through-the-weld and pull-out [31][32][33] fractures. The first one was a shear fracture, in which the nugget remained partially on the bottom sheet [34]. ...
To solve problems in dissimilarly light metal joints, refilled friction stir spot welding (RFSSW) is proposed instead of resistance spot welding. However, rotation speed, dwell time, plunge depth, and the diameter of welding tools all have a great influence on joints, which brings great challenges in optimizing welding parameters to ensure their mechanical properties. In this study, the 1.5 mm thick 2A12Al and 2 mm thick 7B04Al lap joints were prepared by Taguchi orthogonal experiment design and RFSSW. The welding tool (shoulder) diameters were 5 mm and 7 mm, respectively. The macro/microstructures of the cross-section, the geometrical characteristics of the effective welding depth (EWD), the stir zone area (SZA), and the stir zone volume (SZV) were characterized. The shear strength and failure mode of the lap joint were analyzed using an optical microscope. It was found that EWD, SZA, and SZV had a good correlation with tensile–shear force. The optimal welding parameters of 5 mm diameter joints are 1500 rpm of rotation speed, 2.5 mm of plunge depth, and 0 s of dwell time, which for 7 mm joints are 1200 rpm, 1.5 mm, and 2 s. The tensile–shear force of 5 mm and 7 mm joints welded with these optical parameters was 4965 N and 5920 N, respectively. At the same time, the 5 mm diameter joints had better strength and strength stability.
... For rail tracks in a corrosive environment, pits generally form on the surface of the rail, especially at the bottom of the rail foot [11,36]. This causes stress concentration under the superposition of internal stress and alternating axial loads, resulting in fatigue cracking [37]. Subsequently, the cracks experience sustained growth under service conditions above the crack growth threshold, which ultimately leads to the fatigue fracture of the rails [29]. ...
The microstructural evolution and corrosion behaviour of railroad flash-butt-welded U71Mn joints and the effect of heat treatment were investigated via scanning electron microscopy and electrochemical measurements. The joint structures were found to mainly comprise pearlite and a few ferrites. The grains became finer and more homogeneous after heat treatment. Additionally, there was a decrease in the corrosion current density (1.71 × 10−5 A cm−2) and increases in the absolute corrosion potential (0.86 mV) and corrosion resistance (1088.83 Ω−1cm2). This was primarily attributed to the fewer Cl− ions at the homogeneous grain boundaries and fewer oxidation reactions on the joints after heat treatment. The findings of this study explain corrosion failure and will guide the development of corrosion-resistant joints for improved railroad quality.
... Microscopic analysis showed that no refill void defects were found only at the low rotational speed of 900 r/min ( Figure 4(a-d)). As the rotation speed increases, the material with enhanced fluidity during the welding process was lost through the gap between the sleeve and clamping ring, which resulted in insufficient remaining material for refilling and thus leads to the formation of refill void defects [29][30][31]. Annular groove defects ( Figure 4(f)) were observed at the assembly clearance between the clamping ring and the sleeve. Similar to refill voids, it was related to material loss caused by material flow in the stirring process [24,32]. ...
In this study, the refill friction stir processing (RFSP) method was utilised to repair a exit-hole defect located at the end of the friction stir welding (FSW) joints in 7475 aluminium alloy plate. The morphology, macroscopic defects, and mechanical properties of the repaired joints were investigated. The results demonstrate that the exit-hole was successfully refilled after RFSP. Material flow caused the refill voids, annular grooves, and un-stirred material defects. The maximum strength reached 415 Mpa, equal to 105% of the base defect-free weld. The mechanical properties of repaired joint were largely influenced by the stir zone (SZ) boundary and un-stirred material defects.
... However, the plastic material may flow insufficiently under unsuitable welding parameters in the FSW process, resulting in void defects in the joint [4]. Moreover, the changes in temperature and velocity fields, strain rates, and other factors can cause voids to form in components near the tool pin [5,6]. Accordingly, the mechanical properties of the joint will be adversely affected [7e9]. ...
Experiments have proven tool tilting in friction stir welding (FSW) can effectively suppress the formation of void defects. However, the mechanism of tool tilting on suppressing the formation of void defects has not been revealed. In this study, a CFD model considering the influence of tool tilting is established. A non-uniform distribution of normal pressure at the tool-workpiece contact interfaces is proposed to relate to the tool tilt angle. The discrete particle tracing method is used to characterize the formation of void defects in FSW. The heat generation, temperature distribution and plastic flow behaviors between the case without (i.e. 0° tool tilt angle) and with (i.e. 2.5° tool tilt angle) tool tilting are quantitatively compared and analyzed. The results show the tool tilting in FSW leads to higher heat flux and temperature near the pin side in the middle and low parts of the workpiece. Moreover, the frictional shear stress at the pin side/workpiece contact interface significantly increases when the tool is tilting, leading to a higher driving force for the plastic material to flow. As a result, the material flows farther to the advancing side of the workpiece after bypassing the tool when the tool is tilting at 2.5°, which helps to heal the voids on the advancing side of the FSW joints. The higher temperature with higher frictional shear stress enhances the plastic material flow in the middle and low part of the joints when the tool is tilting, which is attributed to suppressing the void defects. The model is validated by experimental results.
... [38]. The characteristics of the fracture surface shown inFigure 8cresult in lower tensile shear strength. ...
This study aimed to investigate how the depth-to-width (D/W) ratio of the welding area affects the welding quality of the SSM6061 aluminum alloy via the friction-stir spot welding (FSSW) process. The results showed that a higher D/W ratio directly results in better mechanical properties. If the D/W ratio value is high (at 1.494), then this leads to higher tensile shear strength at 2.25 kN. On the other hand, if the D/W ratio values are low (at 1.144), then this reduces tensile shear strength to 1.17 kN. The fracture surface behavior on the ring zone also affects the characteristics of ductile fracture. During Vickers hardness analysis, the hardness profiles are in the shape of a W; the maximum hardness was 71.97 HV, resulting from the rotation speed of 3500 rpm and the dwell time of 28 s, where the hardness of the base metal was at 67.18 HV. Finite element (FEM) analysis indicated that the maximum temperature during simulation was 467 °C in the region near the edge shoulder tool, which is 72.96% of the melting point. According to FEM simulation, the temperature under the tool pin region was 369 °C. The generated heat was sufficient to induce changes in the microstructure. For microstructure changes, the globular grain took on a rosette-like form, and coarse grains were observed in the thermal mechanical affect zone (TMAZ) and in the nugget zone (NZ), transforming in the mix zone. Hooks, kissing bonds, voids, and porosity are the defects found in this experiment. These defects indicate a discontinuity in the NZ that leads to worse mechanical properties. During examination via SEM and energy dispersive X-ray (EDX) analysis, the recrystallization structure from β-Mg2Si IMCs to Al3Mg2 and Al12Mg17 IMCs was observed. The size was reduced to an average width of 1–2 µm and an average length of 2–17 µm. Simultaneously, the oxides from the ambient atmosphere present during welding showed dominant partial elements from SiO2, MgO, and Al2O3.
... The study is done to correlate the additional filling on joint formation characteristics and mechanical properties of the joint. It was observed that filling material was sited at the joint's top surface, and the squeezing action of the filling material j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 2 ; 2 0 : 3 0 2 5 e3 0 6 0 increased the effect of reverse and radial extruding of stir zone material and material in the lap interface outside the stir zone at the refilling stage [100,101]. FSSW improved the mechanical properties of advanced ultra-high-strength steel (1.2 mm thick DP1180), followed by water cooling [102]. The experiments are carried out with different parameters (rotation speed: 400 and 600 rpm; plunge speed: 5 mm/min; depth of 1 mm; and dwell time: 10s) and analysed the mechanical properties. ...
Friction-stir techniques are the potential alternative to fusion-based systems for processing and welding metallic alloys and other materials. This review explores the advantages, applications, limitations, and future directions of seven friction-based techniques namely, Additive Friction Stir Deposition (AFSD), Friction Stir Additive Manufacturing (FSAM), Friction Stir Welding (FSW), Friction Stir Processing (FSP), Friction Surfacing (FS), Friction Stir Spot Welding (FSSW), and Friction Stir Lap Welding (FSLW). The basic underlying principle of these processes uses friction as a thermal energy source to weld/process/deposit materials. The common control parameters of all friction stir processing techniques are axial force, rotational speed, and weld or traverse speed. In addition, tool profiles and tool dimensions are known to influence the weld quality. The tool’s rotational speed and axial force generate friction between the workpiece and tool material interface, which could plasticize the material. The additive powder bed friction stir process (APBFSP) is another new solid-state manufacturing technique that focus on fabricating the polymer matrix nanocomposites (PNC). In this, a hollow tool like AFSD and the fundamental principle of FSP are combined. The said parameters affect the quantity of material getting deposited/welded. However, weld speed/traverse speed alters the weld quality, and higher traverse speed results in porosity and voids in the welded/deposited/processed region. The only difference between AFSD and other friction stir techniques (FSTs) is that in the AFSD technique, the hollow rotating tool comprises two protrusions with different tool profiles (cylindrical, threaded cylindrical, and tapered cylindrical, square) used. Threaded cylindrical profile and tool steel as the tool material is the most commonly employed in FSTs. Apart from that, tungsten carbide is preferred for hard materials. The working principles and process parameters of FSTs that affect the part quality are discussed in detail. The above review gives the reader an understanding of the domain of FSTs that can be researched further. A summary of some of the potential research works with objectives, process parameters, and outcomes is highlighted. This will provide the readers with an overview of the work carried out by researchers across the globe. Finally, the potential research gaps for future directions to be explored soon across the globe are outlined.
... Many recent studies have focused on failure mechanisms of RFSSW aluminium alloy joints [21][22][23][24][25][26][27]. Zou et al. [21] found that the weak bonding length at the thermo-mechanically affected zone (TMAZ)/stir zone (SZ) interface and the bending height of hook defects had the strongest effects on shear plug fracture mode. ...
... Sara et al. [25] analysed tensile shear testing using finite-element analysis, and found that a stress concentration exists at the hook during a test; however, the relationship between expansion of cracks and strain distribution during the fracture process is not known. The effect of hook defects on mechanical properties was reduced, but not eliminated, using material filling [26] and parameter optimisation [27]. Therefore, intuitive testing and characterisation are required to further investigate the fracture process and mechanism. ...
... Figure 5 shows a cross-section of an RFSSW joint with a symmetrical basin shape in which the SZ, TMAZ, HAZ, and BM are identified [24,32]. The lap interface exhibited upwards bending at both sides and refill pore defects did not occur [26]. Hook defects existed on the ringside of the lap interface, and changed from a downwards bend to an upwards bend at plunge depths larger than the thickness of the upper plate. ...
The mechanical properties and failure process of 2 mm-thick 5052 Al and 6 mm-thick 2A12 Al fabricated by refill friction stir spot-welding were investigated. The hooks were bent respectively downwards and upwards at plunge depths smaller and larger than the upper plate thickness. The joint area of the lap interface and bearing thickness of the upper plate were related to the hook direction. The tensile shear failure load was affected by structural characteristics and hardness of the joints. Stress concentration occurred in the hook and strain expanded with the hook during fracture. There were two fracture modes: shear fracture and shear plug fracture, where both cracks passed through the hook and fracture morphology of the hook was less plastic.
... The obtained images show that the presence of defects (e.g., voids, lack of bonding or of mixing, incomplete refill, etc.) was not detected in any of the analyzed welds. According to Wang et al. [48], the lack of volume defects indicates that the frictional heat generated by the shoulder and probe was enough to plasticize the material. This demonstrates that the observed tool wear did not reach the critical point to introduce defects inside the analyzed welds. ...
The Refill Friction Stir Spot Welding (RFSSW) process—an alternative solid-state joining technology—has gained momentum in the last decade for the welding of aluminum and magnesium alloys. Previous studies have addressed the influence of the RFSSW process on the microstructural and mechanical properties of the AA6061-T6 alloy. However, there is a lack of knowledge on how the tool wear influences the welding mechanical behavior for this alloy. The present work intended to evaluate and understand the influence of RFSSW tool wear on the mechanical performance of AA6061-T6 welds. Firstly, the welding parameters were optimized through the Designing of Experiments (DoE), to maximize the obtained ultimate lap shear force (ULSF) response. Following the statistical analysis, an optimized condition was found that reached a ULSF of 8.45 ± 0.08 kN. Secondly, the optimized set of welding parameters were applied to evaluate the wear undergone by the tool. The loss of worn-out material was systematically investigated by digital microscopy and the assessment of tool weight loss. Tool-wear-related microstructural and local mechanical property changes were assessed and compared with the yielded ULSF, and showed a correlation. Further investigations demonstrated the influence of tool wear on the height of the hook, which was located at the interface between the welded plates and, consequently, its effects on the observed fracture mechanisms and ULSF. These results support the understanding of tool wear mechanisms and helped to evaluate the tool lifespan for the selected commercial RFSSW tool which is used for aluminum alloys.
... This type of method for calculating fatigue life was based on the Palmgren-Miner Rule, regardless of the loading sequences [17]. The second approach included fracture mechanics [18], in which it assumed that the fatigue life was mainly composed of the following three parts: crack initiation, propagation, and final instantaneous fracturing. However, the principles behind fatigue failure remain unclear, at least according to the aforementioned traditional methods. ...
It is not completely understood fatigue strength at this time due to its complex formation mechanism. Therefore, in order to address this issue, machine learning has been used to examine the important factors involved in predicting fatigue strength. In this study, a hybrid model was proposed based on the modified bagging method by combining XGBoost and LightGBM, in which the hyperparameters of the models were optimized by a grey wolf algorithm. Moreover, an interpretable method, referred to as Shapley additive explanations (SHAP), was introduced to explain the fatigue strength predictions made by ML models. The SHAP values were calculated, and feature importance of fatigue strength by XGBoost, LightGBM and the hybrid model was discussed. The final results demonstrated that the SHAP method had major potential for interpreting fatigue strength predictions, which would provide constructive guidance for the development of antifatigue steel material in the future.
... With the rapid improvement of industrial technology, aluminum (Al) alloy has been widely used in the manufacturing field [1][2][3][4]. As a kind of high strength Al alloy, LC9 (7A09) alloy is one of the most remarkable alloys in China. ...
In this paper, WC-10Co4Cr coating was prepared on the surface of LC9 aluminum alloy by high velocity air-fule (HVAF) process. And a thermal deformation method was developed to enhance the coating properties. Experimental results show that, during the process of thermal deformation, the increase of temperature and deformation amount could improve the microhardness of coating surface. With temperature of 480 °C and deformation amount of 16% (0.8 mm), the microhardness reached the maximum value of 1349 HV0.3, which increased nearly 20% compared with that of specimen (1137 HV0.3) without compressive deformation. Besides, the strengthening effects of thermal deformation temperature and deformation amount on the bonding strength of coating were obvious. With deformation temperature of 450 °C and deformation amount of 8% (4 mm), the bonding strength reached the maximum critical load of 188 N, which was 17.5% higher than that of initial state.
