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Insight on corrosion behavior of friction stir welded AA2219/AA2195 joints in astronautical engineering
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Corrosion behavior of friction stir welded Al-Cu alloy and Al-Cu-Li alloy joints were revealed via immersion, intergranular, exfoliation and electrochemical corrosion. Precipitation-driven corrosion was discussed based on experiments and theoretical modeling. The corrosion potential of the entire joint was nobler than base materials, which was mainly attributed to solid solution and precipitation evolution of high equilibrium potential elements. The macro/micro galvanic effect induced by the redistribution of copper was studied with a numerical model to explain the relationship between precipitation evolution and corrosion resistance. Reducing heat input by increasing welding speed was an effective strategy to improve corrosion resistance.
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... FSW achieves joint formation through a combination of frictional heat and plastic deformation, resulting in distinct regions within the joint: the stir zone (SZ), advancing side (AS), retreating side (RS), and base metal (BM) [4][5][6]. The SZ represents the central region where the FSW tool interacts with the workpieces, undergoing significant plastic flow and grain refinement to form a metallurgical bond [7]. The AS and RS refer to the sides of the joint where the FSW tool moves forward and backward, respectively, during welding, with the AS experiencing greater plastic deformation and thermal effects [8,9]. ...
... Notably, Figure 1a highlights that the AS typically exhibits a smoother surface finish compared to the RS. The smoother surface finish observed on the AS compared to the RS in FSW can be attributed to the direction of tool movement [7][8][9]. The tool moves forward on the AS, resulting in more uniform plastic deformation and thermal effects, which can lead to a smoother surface. ...
... In the RS, depicted in Figure 3c, the microstructure displays evidence of deformation, such as elongated grains or flow pa erns, caused by the movement of the FSW tool away from the welding direction. This side experiences lower temperatures and less severe plastic deformation compared to the AS [7][8][9]. Conversely, the AS shown in Figure 3d exhibits some degree of deformation and flow pa erns, albeit to a lesser extent compared to the RS. The AS experiences higher temperatures and more intense plastic deformation, resulting in grains that are typically equiaxed, closely resembling the grain structure of the base metal. ...
The reliability of friction stir welded joints is a critical concern, particularly given their potential applications in the aerospace manufacturing industry. This study offers a quasi-in situ observation of the microstructural response during fatigue crack growth (FCG) of a friction stir welded AA2024-T4 joint, aiming to correlate fatigue crack growth behavior with mechanical properties investigated using electron backscatter diffraction (EBSD). Notched compact tension (CT) specimens corresponding to the morphology of the stir zone (SZ), advancing side (AS), and retreating side (RS) were meticulously designed. The findings indicate that the welding process enhances the joint’s resistance to fatigue crack growth, with the base metal exhibiting a shorter fatigue life (i.e., ~105 cycles) compared to the welding zones (SZ ~ 3.5 × 105 cycles, AS ~ 2.5 × 105 cycles, and RS ~ 3.0 × 105 cycles). Crack propagation occurs within the stir zone, traversing refined grains, which primarily contribute to the highest fatigue life and lowest FCG rate. Additionally, cracks initiate in AS and RS, subsequently expanding into the base metal. Moreover, the study reveals a significant release of residual strain at the joint, particularly notable in the Structural-CT-RS (Str-CT-RS) sample compared to the Str-CT-AS sample during the FCG process. Consequently, the FCG rate of Str-CT-AS is higher than that of Str-CT-RS. These findings have significant implications for improving the reliability and performance of aerospace components.
... For the FSW process of dissimilar Al/Mg alloys, although the generation of intermetallic compounds has an important impact on the joint strength, the change in grain structure also has a critical impact on joint performance, such as corrosion resistance [13]. Therefore, it is necessary to study the grain refinement process in FSW of dissimilar Al/Mg alloys. ...
The process of grain refinement during welding significantly influences both the final microstructure and performance of the weld joint. In the present work, merits of acoustic addition in the conventional Frictions Stir Welding (FSW) process were evaluated for joining dissimilar Al/Mg alloys. To capture the near “in situ” structure around the exit hole, an “emergency stop” followed by rapid cooling using liquid nitrogen was employed. Electron Backscatter Diffraction analysis was utilized to characterize and examine the evolution of grain microstructure within the aluminum matrix as the material flowed around the exit hole. The findings reveal that two mechanisms, continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX), jointly or alternatively influence the grain evolution process. In conventional FSW, CDRX initially governs grain evolution, transitioning to GDRX as material deformation strain and temperature increase. Subsequently, as material deposition commences, CDRX reasserts dominance. Conversely, in acoustic addition, ultrasonic vibration accelerates GDRX, promoting its predominance by enhancing material flow and dislocation movements. Even during the material deposition, GDRX remains the dominant mechanism.
... Moreover, the production of sound-quality welds is significantly influenced by the irregular grain structure along the interface [15,16]. Therefore, the research concerning the grain structure that occurs during dissimilar welding needs to be explored in more detail. ...
The trade-off between welding and strength loss during dissimilar metals joining has been important for decades. Strength loss minimization is essential for industries. The current study investigates the microstructure clarification in the nugget zone (NZ) of AA7075/AZ31B dissimilar friction stir welded joints with or without ultrasonic vibration (UV) at different tool offset conditions. The reduction of incomplete dynamic recrystallization towards the AA7075 side and its transformation into complete dynamic recrystallization (DRX) were observed through the analysis of the grain microstructure, which showed that ultrasonic vibration improved dislocations and grain boundaries. Texture analysis discloses high-strain texture towards the AA7075 side, whereas less complex stresses texture for the AZ31 side under UV. Moreover, the grain refinement on both sides of the interface also affects the joint tensile strength. The maximum strength was obtained with ultrasonic vibration. The Schmid factor results reveal that the UV has a minor influence on the slip system towards the Al side. Conversely, it activates the twining system towards the AZ31 side.
... The bottom part of the weldment had more heat dissipation and less heat input, and the welding temperature was relatively low compared to the upper part of the weldment. Low temperature caused less precipitate to dissolve again [33], and the corrosion resistance of the bottom of the weldment was poor. Reducing the temperature difference in the thickness direction of the weldment could improve the uniformity of temperature distribution and increase the temperature of bottom part of the weldment [8], thereby increasing the dissolution of precipitate at the bottom part of the welded joint, achieving more effective suppression of galvanic corrosion effect, and thus improving the overall corrosion resistance of the welded joint. ...
The thick large circular storage tank of heavy launch vehicle is made of 2219 aluminum alloy and welded using friction stir welding (FSW) technology. To explore the temperature distribution of friction stir girth welding in circular storage tank and select welding parameters, a simulation model of temperature field is established based on ABAQUS/CEL method, combining the amplitude-periodic function to define the mechanical boundary condition and implement motion synthesis based on the parallelogram rule to realize the trace setting of the tool during welding stage of girth welding. The simulation model is verified through temperature measurement with infrared thermal imager. By comparing with the temperature field of FSW plate, the temperature distribution rule of girth welding circular tank is explored. Optimizing with the goals of reducing the length of heat-affected zone and the temperature difference in the thickness direction of the weldment, the process parameters are obtained based on the response surface method–multi-objective particle swarm optimization algorithm. The Pareto optimal solution set is obtained which provides guidance for the selection of welding process parameters.
... This can be attributed to its finer grain structure and the presence of a higher wt% of Al 2 TiO 5 particles at the grain boundaries. This effectively weakens micro-galvanic degradation, enhancing the overall corrosion resistance of sample W15 [45]. The presence of Al 2 TiO 5 particles in the composites serves as an insulating path, hindering the formation of galvanic cells between the two combined composites [21]. ...
This study investigates the impact of friction stir welding (FSW) parameters on dissimilar AA5052-Al 2 TiO 5 /AA6061-Al 2 TiO 5 composite joints. Tool rotational speed (TRS), feed rate, and aluminum titanate (Al 2 TiO 5) content are varied, and their influence on microstructure, mechanical properties, wear resistance, and corrosion behavior is assessed. Joints fabricated with 1200 rpm TRS, 40 mm/min feed rate, and 2 wt% Al 2 TiO 5 exhibit the highest tensile strength (170.11 MPa) due to grain refinement in the stir zone (SZ). Joints with 3 wt% Al 2 TiO 5 have near-base composite hardness (86.12 HV) and exhibit distinct microstructures across different zones. Samples with superior mechanical properties display finer grains in the SZ, while other zones exhibit elongated grains. The sample reinforced with 3 wt% Al 2 TiO 5 (W9) demonstrates enhanced wear resistance attributed to its high hardness. Additionally, the sample fabricated with 1200 rpm TRS, 40 mm/min feed rate, and 2 wt% Al 2 TiO 5 (W15) displays the lowest corrosion rate (0.44 mpy) due to its fine structure. Fracture analysis reveals different failure mechanisms in tensile and wear testing.
The dissimilar butt joining of aluminum alloy and copper was successfully realized by cold metal transfer (CMT) welding–brazing with the help of preheating on copper. Preheating could balance the effect of the high thermal conductivity of copper on weld formation, and eliminate welding defects such as porosity, unfused zone, and cracks at the interface. Three layers of intermetallic compounds were observed at the brazing interface, namely, Al4Cu9, Al2Cu3, and Al2Cu. When the heat input was reduced to 648 J/mm, the total thickness of the interfacial IMC layers was suppressed to 4.83 μm, and the mechanical property of the joint was up to 91.35 MPa. The corrosion resistance of the Al/Cu welded joint was worse than that of the base metals, and corrosion occurred at the interfacial IMCs and the grain boundaries of the weld microstructure.
Ultra-refined grains were obtained in few-layer graphene nanoplatelets reinforced aluminum matrix composites via deformation-driven metallurgy under coupled thermo-mechanical effect. Fragmentation, thinning and re-dispersion of the reinforcements accelerated the nucleation of recrystallized grains and inhibited the migration of grain boundaries. The synergy grain refinement mechanism led to a greatly refined microstructure with an average grain size of 267.0 nm, which was much smaller than the grain size of conventional aluminum matrix composites to realize high strengthening-toughening efficiency. This novel preparation route showed the capacity of developing ultra-fine aluminum matrix composites with the exceptional grain refinement towards ultra-lightweight design.
Friction stir process (FSP) has been utilized to modify the surface microstructure of AZ91 alloy in three levels of rotation speeds and pass numbers. Microstructural and electrochemical analyses were performed on as-received and FSPed alloys, and their correlation was investigated. Optical and electron microscopy showed a significant grain refinement, accompanied by aluminum's dissolution into the matrix phase. The highest aluminum over-saturation occurred at 1200 rpm, which led to eutectic phase discontinuity at the grain boundaries. Additionally, the basal plane texture was studied using pole figures of the surface, which revealed extreme basal texture after the FSP. Utilization of X-ray diffraction (XRD) to calculate the residual stress before and after the FSP indicated substantial residual stress build-up. Accumulation of the eutectic phase at the grain boundaries led to the shift of the open circuit potential (OCP) toward more positive values in a 3.5% NaCl solution. Moreover, according to the electrochemical analyses, the corrosion rate increased after the FSP. At 1200 rpm of the rotation speed, more severe aluminum dissolution into the matrix phase increased surface layer resistance to breakdown. It was also observed that the accumulation of higher eutectic phases at the grain boundaries induces more galvanic microcells, which caused a drop of charge transfer resistance.
Root-like structure on C/SiC surface has been designed through selective corrosion to decrease the residual stress and then to optimize the microstructure when brazed to Nb. Thermal and electrochemical corrosion are conducted to diminish the SiC matrix and the interface between carbon fibers and SiC, respectively. The surface structure can be filled with brazing alloy characterized by the gradient layer of carbon fiber reinforced brazing alloy. Compared with thermal corrosion, SiC particles and nano Ti5Si3 are uniformly dispersed throughout the gradient layer in electrochemical corrosion. The layer decreases the difference in property consequently to relieve the residual stress. In addition, the original reaction layer will be replaced by this layer, favorable for the increase in joining strength and fracture toughness. The brittle facture at the reaction layer in original joints can be transformed into the zig-zag path. The shear strength of joints with the thermal and electrochemical corrosion depth of 100 μm increases to 151.6 MPa and 164.3 MPa, respectively, which is 77% and 92% higher than that of original joints.
In this study, the microstructure and corrosion resistance of the stir zone (SZ) of the AA2198-T8 Al-Cu-Li alloy welded by friction stir welding (FSW) were investigated by microscopy, immersion tests and electrochemical techniques such as measurements of open circuit potential variation with time, and scanning vibrating electrode technique (SVET) measurements. A low chloride-containing solution (0.005 mol L⁻¹ NaCl) was employed in the corrosion studies and severe localized corrosion (SLC) was observed in the SZ related to intergranular attack. The results were compared to those of the non-affected areas by FSW, also known as base metal (BM). In the BM, SLC was found and the type of attack related to it was intragranular. In both zones, BM and SZ, SLC was due to precipitates of high electrochemical activity, specifically T1 (Al2CuLi) phase in the BM, whereas TB (Al7Cu4Li) / T2 (Al6CuLi3) in the SZ. Scanning vibrating electrode technique (SVET) analysis was very useful in the study of SLC in the AA2198-T8 alloy showing the development of high anodic current densities at the mouth of the SLC sites.
The intergranular corrosion (IGC) and the microstructures in B4C-reinforced 6061Al composite were investigated in the present work. IGC only occurred in the Cu-containing samples. The artificial aging decreased the IGC resistance of the composite. Corrosion propagated through the aluminum grain boundaries as well as the B4C/Al interfaces. The microstructures characterizations by transmission electron microscopy (TEM) indicated that a continuous Cu-rich layer with width of 3.5 nm along grain boundary was responsible for the IGC susceptibility of aged Cu-containing sample.
We proposed a severe plastic deformation process named friction stir extrusion to fabricate high-strength-and-ductility rare-earth containing Mg alloys. Grain refinement and homogeneously-dispersion of second-phases were obtained under the coupling thermo-mechanical effect, which resulted in the yield strength, ultimate strength and compression strain increased by 42.5%, 63.6% and 35.5% respectively.
The solid-state structural modification technique friction-stir-processing (FSP) was applied on the surface of a laser-powder-bed-fusion fabricated AlSi10Mg alloy to locally modify the microstructure and enhance the corrosion properties of the alloy. A uniform microstructure was formed after FSP, comprised of a homogenous distribution of the Si-particles embedded in an Al-matrix with an ultrafine-grained structure containing a low fraction of subgrains, and reduced porosity level. This structure offers improved corrosion properties, ascribed to the formation of a thicker passive layer with a lower donor density on the FSPed regions as compared to the as-fabricated metal.
Anodic aluminum oxide films, industrially produced by anodizing aluminum alloys under the galvanostatic mode at a relatively low temperature of 20°C (electrolyte bath temperature), present the reliable anticorrosive effect for numerous applications. For fabricating anodic aluminum oxide films with the promising corrosion resistance as well as high growth rate in a wide temperature range, the effect of anodizing temperatures on the structure and growth mechanism of anodic aluminum oxide films was investigated. As the temperature increases up to 30°C, the stress-driven breakdown of porous-type anodic aluminum oxide layers induced by their thinner pore walls was estimated. This phenomenon is interpreted by an increase of electronic current and thus a strong scour effect of O2 bubbles on the porous-type anodic aluminum oxide layers. Moreover, with the addition of composite organic acid into the sulfuric acid-based electrolyte solution, the anions (C6H5O73−,C4H4O62−) that incorporated into the anodic oxide contribute to lowering the electronic current and thus suppressing the formation of oxygen bubbles, resulting in a thicker barrier-type anodic aluminum oxide layer. This is assumed to be responsible for the enhanced corrosion resistance of anodic aluminum oxide films prepared at 30°C with 50 g/L organic acid addition.
The new generation high Zn-containing 7xxx series aluminum alloys were more prone to stress corrosion cracking (SCC) compared with the traditional 7xxx series aluminum alloys. However, the effect of grain boundary precipitates (GBPs) characteristics, especially microchemistry, on SCC of new generation high Zn-containing 7xxx series aluminum alloys were not investigated in sufficient detail. In the paper, the GBPs characteristics of a new generation high Zn-containing 7056 aluminum alloy were prepared by different aging heat treatments. The morphology and microchemistry of GBPs were analyzed by transmission electron microscope equipped with super-X energy disperse spectroscopy. The stress intensity factor (KI) and SCC propagation velocity(v) were measured by double cantilever beam (DCB) experiment. The correlations between the GBPs microchemistry and SCC resistance had been discussed. The results showed that the SCC resistance of a new generation high Zn-containing 7056 aluminum alloy was significantly improved by high termination temperature non-isothermal aging and re-aging heat treatment compared with T6 and T77 aging heat treatment. In addition, it was indicated that the SCC resistance was positively with the Cu content of GBPs.