Search Results (717)

To mitigate welding defects and optimize the microstructure of aluminum alloys, this study introduces a multi-pulse hybrid arc welding process. A comparative investigation was carried out between this novel process (AC/DC composite 1 kHz pulsed welding) and conventional methods (AC pulsed, AC/DC pulsed) during wire-fed overlay welding of 6061 aluminum alloy. Analyses were conducted on electrical signals, arc morphology, joint microstructure, and hardness. The results indicate that the AC/DC hybrid 1 kHz pulsed process combines the characteristics of both AC and DC pulsed signals with full-cross-section frequency pulse superposition, thereby optimizing arc welding process control. The frequency pulses induce a magnetoelectric effect, leading to significant arc constriction, which enhances arc energy density and arc pressure. This intensifies the fluid flow in the molten pool and accelerates cooling, thereby suppressing the growth of columnar grains and promoting the formation of fine equiaxed grains and an increased proportion of high-angle grain boundaries. Meanwhile, this process effectively reduces the number, area fraction, and overall porosity, and facilitates the distribution of a large amount of Al–Si eutectic structure along grain boundaries, enhancing the impediment to dislocation motion. The microstructural optimization significantly improves the hardness at the weld center to 73.1 HV, leading to enhanced mechanical properties. Full article

Refill friction stir spot welding (refill FSSW) is a solid-state joining technique that enables dissimilar welding between aluminum and steel alloys with minimal intermetallic compound (IMC) formation. Previous studies have focused on the interfacial mechanical performance of such joints, limited attention has been given to the localized corrosion behavior of the aluminum surface after welding, particularly in relation to microstructural evolution. This study investigates the effect of refill FSSW on the localized corrosion resistance of the aluminum surface in dissimilar joints with DP600 steel, since the Al side is typically the exposed surface in automotive service conditions. Emphasis is placed on the correlation between microstructural changes induced by the welding thermal cycle, such as grain refinement and precipitate coarsening, and localized corrosion behavior. The welded samples were characterized by optical and scanning electron microscopy, Vickers hardness measurements and potentiodynamic polarization techniques. Corrosion tests revealed a slight reduction in corrosion resistance in the stir zone compared to the base metal, mainly attributed to Mg₂Si coarsening. Pit initiation sites were associated with Al(Fe, Mn)Si and Mg₂Si precipitates. These findings offer new insights into the corrosion mechanisms acting on the aluminum surface of refill FSSW joints, supporting the development of more corrosion-resistant dissimilar structures. Full article

The high-Mg-content Al-Mg-Zn-Si alloy, as a novel aluminum alloy, exhibits excellent strength, toughness, and corrosion resistance, demonstrating significant application potential in lightweight structural components for aerospace, weapon systems, rail transportation, and other fields. In this study, friction stir welding was employed to weld the high-Mg-content Al-Mg-Zn-Si alloy. Subsequent aging treatment was applied to establish the relationship between the mechanical properties and microstructural characteristics of the welded joint, aiming to elucidate the strengthening mechanisms of the new alloy and provide insights for achieving high-quality welds. The results indicate that the microhardness profile of the as-welded joint exhibited a “W” shape, with overall low hardness values and minor differences between zones. After the aging treatment, the microhardness increased significantly in the base material (BM), the thermo-mechanically affected zone (TMAZ), and the stir zone (SZ), whereas the heat-affected zone (HAZ) adjacent to the SZ exhibited only a marginal increase, making it the softest region in the aged joint. The yield strength and ultimate tensile strength of the aged joint increased to 327 MPa and 471 MPa, respectively. The enhancement in microhardness and strength after aging treatment was attributed to the precipitation of numerous nano-sized T-phase particles within grains. Interestingly, the tensile samples of the aged joint fractured in the high-hardness SZ instead of the low-hardness HAZ. This fracture behavior was primarily attributed to continuous grain boundary precipitates, which reduced intergranular cohesion. In contrast, the elongated grain structure in the HAZ more effectively resisted intergranular crack propagation compared to the equiaxed grains in the SZ. Full article

In the design and manufacturing of pressure vessels, the quality of welded joints and their operational safety are critical considerations. Weld quality classification is closely linked to its impact on fatigue performance. In this study, aluminum alloy welds with varying levels of porosity were produced by adjusting welding parameters, and X-ray inspection was used to assess porosity levels. Representative welds corresponding to different quality grades were selected to fabricate fatigue specimens, and their fatigue lives were determined. The influence of quality grades on the residual fatigue life of aluminum alloy welded sheets was systematically analyzed. The results indicate that, under identical loading conditions, the fatigue life of specimens with defects is significantly reduced compared to defect-free specimens. This reduction becomes more pronounced as the quality grade decreases—corresponding to an increase in circular hole defects. Specifically, for 5083 aluminum alloy, transitioning from Grade I to Grade III results in fatigue life reductions of approximately 25%, 35%, and 50%, respectively. Full article

Resistance spot welding of aluminum alloys causes the electrode materials to degrade rapidly. This is due to diffusion processes occurring between the sheet materials and the copper electrodes at process temperatures of up to 600 °C. This significantly limits the electrode life, resulting in less than 60 weld cycles before the joint quality becomes insufficient. Thin-film diffusion barriers can increase electrode life and improve joint quality. This article describes the generation of barrier layers of nickel and tungsten using physical vapor deposition. These layers directly influence the welding process by altering the electrical resistance and friction coefficients in the contact area. Nanoindentation is used to determine the specific properties of the barrier layers within the 2.5–3 µm layer thickness range. Hardness and modulus of elasticity are determined by indentation tests. Scratch tests determine the friction coefficients and adhesion strength of the coating against plastic deformation. Nanoindentation is also used to investigate the degradation process of the electrode base material and barrier layers. This reveals which damage mechanisms occur with uncoated electrodes and demonstrates how thin-film diffusion barrier coatings can prevent aluminum diffusion. Full article

Additive manufacturing (AM), particularly laser-based powder bed fusion (PBF-LB), enables the production of high-strength, lightweight components made of aluminum alloys such as AlSi10Mg. However, joining these parts via welding remains a significant challenge due to weld seam porosity caused by hydrogen entrapment. This study investigated the influence of the PBF-LB process parameters, tungsten inert gas (TIG) welding settings, filler material, and post-weld T6 heat treatment on the tensile strength and porosity of welded AlSi10Mg components. Using two different layer heights (30 µm and 60 µm), plate thicknesses (3 mm and 5 mm), and varying welding conditions, a series of 10 TIG-welded sample groups were fabricated and analyzed. Microstructural, hardness, porosity, and tensile tests revealed that porosity was high across all samples (11–19%). A subsequent T6 heat treatment improved the tensile strength. Higher layer heights and thinner plates led to a higher tensile strength of the weld seam, while the addition of a filler material showed limited benefits. No other influencing factors or interactions could be found. The results emphasize the need to optimize hydrogen control in the processes, melt pool dynamics, and weld seam geometry to receive reliable joints in lightweight manufacturing of PBF-LB AlSi10Mg parts. Full article

This study presents an integrated experimental and numerical investigation of the Refill Friction Stir Spot Welding (RFSSW) process applied to dissimilar aluminum alloys. The primary objective is to evaluate the mechanical and thermal behavior of the joints and to identify key process parameters influencing weld quality. Experimental welding trials were performed on aluminum alloy sheets using RFSSW, followed by shear testing and metallographic analysis to assess joint integrity, microstructure evolution, and fracture behavior. Infrared thermography and temperature sensors were employed to monitor heat distribution during welding. In parallel, a finite element model was developed to simulate the thermal cycle and stress distribution within the welded region. The numerical results showed good agreement with the experimental data, particularly regarding peak temperature and cooling trends at specific distances from the tool center. The findings demonstrate that RFSSW can successfully join dissimilar aluminum alloys with minimal defects when optimized parameters are applied. The combination of experimental observations and FEM simulation provides valuable insights into the underlying thermomechanical phenomena and offers a foundation for further process optimization. Full article

Friction stir additive manufacturing (FSAM) is a promising solid-state technique for fabricating high-strength aluminum alloys, such as Al-7075, which are difficult to process using conventional melting-based additive manufacturing (AM) methods. This study investigates the mechanical properties and tool wear behavior of seven-layered Al-7075 multi-layered composites reinforced with silicon carbide (SiC) and titanium carbide (TiC) fabricated via FSAM. Microstructural analysis confirmed defect-free multi-layered composites with a homogeneous distribution of SiC and TiC reinforcements in the nugget zone (NZ), although particle agglomeration was observed at the bottom of the pin-driven zone (PDZ). The TiC-reinforced composite exhibited finer grains than the SiC-reinforced composite in both as-welded and post-weld heat-treated (PWHT) conditions, achieving a minimum grain size of 1.25 µm, corresponding to a 95% reduction compared to the base metal. The TiC-reinforced multi-layered composite demonstrated superior mechanical properties, attaining a microhardness of 93.7 HV and a UTS of 263.02 MPa in the as-welded condition, compared to 88.6 HV and 236.34 MPa for the SiC-reinforced composite. After PWHT, the TiC-reinforced composite further improved to 159.12 HV and 313.46 MPa UTS, along with a higher elongation of 11.14% compared to 7.5% for the SiC-reinforced composite. Tool wear analysis revealed that SiC reinforcement led to greater tool degradation, resulting in a 1.17% weight loss. These findings highlight the advantages of TiC reinforcement in FSAM, offering enhanced mechanical performance with reduced tool wear in multi-layered Al-7075 composites. Full article

The high-strength aluminum alloy 7B04 used in aircraft structures poses challenges in welding. In this study, 7075 aluminum alloy powder is used as an interlayer to strengthen the vacuum diffusion bonding (DB) joint of 7B04 aluminum alloy. Surface treatments with plasma activation before DB can effectively increase the bonding rate and lap shear strength (LSS) of the joint. The effects of DB temperature, pressure, and holding time on the joint LSS were analyzed by developing a quadratic regression model based on the response surface method (RSM). The model’s determination coefficient reached 99.52%, with a relative error of about 5%, making it suitable for 7B04 aluminum alloy DB process parameters optimization and joint performance prediction. Two sets of process parameters (505 °C-5.7 h-4.5 MPa and 515 °C-7.5 h-4.4 MPa) were acquired using the satisfaction function optimization method. Experimental results confirmed that the error between measured and predicted LSS is approximately 5%, and a higher LSS of 174 MPa was achieved at 515 °C-7.5 h-4.4 MPa. Full article

This study systematically investigates the effects of welding current on the macro-morphology, microstructure, mechanical properties, and corrosion resistance of Cu-Mn-Al alloy coatings deposited on 27SiMn steel substrates using Cold Metal Transfer (CMT) technology. The 27SiMn steel is widely applied in coal mining, geology, and engineering equipment due to its high strength and toughness, but its poor corrosion and wear resistance significantly limits service life. To address this issue, a Cu-Mn-Al alloy (high-manganese aluminum bronze) was selected as a cladding material because of its superior combination of mechanical strength, toughness, and excellent corrosion resistance in saline and marine environments. Compared with conventional cladding processes, CMT technology enables low-heat-input deposition, reduces dilution from the substrate, and promotes defect-free coating formation. To the best of our knowledge, this is the first report on the fabrication of Cu-Mn-Al coatings on 27SiMn steel using CMT, aiming to optimize process parameters and establish the relationship between welding current, phase evolution, and coating performance. The experimental results demonstrate that the cladding layer width increases progressively with welding current, whereas the layer height remains relatively stable at approximately 3 mm. At welding currents of 120 A and 150 A, the cladding layer primarily consists of α-Cu, κII, β-Cu₃Al, and α-Cu + κIII phases. At higher welding currents (180 A and 210 A), the α-Cu + κIII phase disappears, accompanied by the formation of petal-shaped κI phase. The peak shear strength (509.49 MPa) is achieved at 120 A, while the maximum average hardness (253 HV) is obtained at 150 A. The 120 A cladding layer demonstrates optimal corrosion resistance. These findings provide new insights into the application of CMT in fabricating Cu-Mn-Al protective coatings on steel and offer theoretical guidance for extending the service life of 27SiMn steel components in aggressive environments. Full article

Laser welding of 6061 aluminum alloy often results in coarse microstructures and inferior corrosion resistance due to rapid solidification. This study introduces ultrasonic vibration as an auxiliary technique to address these limitations. The paper systematically investigates the influence of laser weld ultrasonic assistance on the microstructure and corrosion behavior of a 6061-T6 aluminum alloy welded joint. The results demonstrate that ultrasonic assistance refined the grain structure and reduced the corrosion current density by 19.1% compared to conventional laser welding, achieving 73.6% of the base metal’s corrosion resistance. The enhancement is attributed to ultrasonic-induced acoustic streaming and cavitation, which promote equiaxed grain formation and impede corrosive penetration. The enhancement is attributed to ultrasonic-induced acoustic streaming and cavitation, which promote equiaxed grain formation and impede corrosive penetration. Under the ultrasonic effect, the number of dimples in the weld fracture increased and the depth was significant, which enhanced the tensile strength of the 6061 Aluminum alloy weld. This work provides a reliable and efficient strategy for producing high-performance aluminum alloy welded structures in industrial applications. Full article

The application of lightweight materials in the automotive industry can effectively achieve further weight reduction while maintaining overall structural strength, thereby reducing energy consumption. Currently, friction stir spot welding (FSSW) is the primary method for joining carbon fiber-reinforced polyphenylene sulfide (CF-PPS) with aluminum alloys. This study successfully achieved the connection between 6061-T6 aluminum alloy and CF-PPS using the more operationally convenient friction stir lap welding (FSLW) technique. The primary objective of this study was to explore the potential of expanding the welding technologies available for successfully joining these two dissimilar materials. The joint morphology and strength were analyzed through metallographic observation and tensile testing, and the effects of different welding parameters on the microstructure and mechanical properties of dissimilar joints were studied. The study demonstrated that the successful connection between AA6061-T6 and CF-PPS was primarily attributable to the combined effects of mechanical interlocking and mixture bonding. The joint strength demonstrated a maximum value of 9.41 MPa when the following parameters were set: a rotation speed of 1800 rpm, a welding speed of 40 mm/min, and a plunge depth of 0.2 mm. Although low rotation speed and low welding speed cannot form an effective mechanical interlocking structure for the joint, the failed joints have different causes. When the rotation and welding speeds are fixed, changing the plunge depth cannot change the interlocking structure of the joint. A larger plunge depth will thin the weld and greatly reduce the joint strength. Full article

The keyhole defect located at the termination of the friction stir welding (FSW) seam of 6082 aluminum alloys was repaired utilizing the refilling friction stir spot technique. This study examined the impact of the plunge depths on the microstructure of the welding spot. The results show that under the action of shear stress introduced by the pin, the (111)[1$\overline{1}$0] shear texture and (112)[11$\overline{1}$] Copper texture were formed. The formation of (001)[100] Cube and (001)[310] Cube_ND textures was due to the occurrence of discontinuous dynamic recrystallization. When the plunge depth of the sleeve was 1.0 mm, the volume fraction of deformed grains in the welding spot reached 45%, and the tensile strength of the welding spots was 184 MPa. When the plunge depth of the sleeve was 1.5 mm, the tensile strength of the repaired spot welding was 210 MPa, which was basically equal to the strength of the FSW seam. Full article

Ultrasonic-assisted friction stir lap welding (FSLW) was employed to join dissimilar aluminum alloys, namely Al-7075 and Al-5052. The effect of ultrasonic power on the weld performance was systematically investigated. Increasing the ultrasonic power enhanced the material flow, resulting in a significant reduction in the cavity area in the nugget zone, from 0.37 mm² to 0.01 mm², as the ultrasonic power was increased from 0 W to 600 W. Simultaneously, increasing the ultrasonic power accelerated the dynamic recrystallization in the nugget zone, refining the grain size by 46%. This grain refinement consequently enhanced the hardness of the nugget zone, yielding an increase of approximately 10 HV. However, the excessive ultrasonic power level of 600 W also amplified the ultrasonic punch effect, inducing interfacial crack formation between Al-7075 and Al-5052 on the advancing side. These defects (cavity and interfacial crack) significantly influenced the joint failure behavior: the non-ultrasonic-assisted FSLW joints failed at the cavity, while the 600 W-ultrasonic-assisted FSLW joints failed along the interfacial crack. Comparatively, an ultrasonic power of 300 W suppressed both the cavity and interfacial crack, producing FSLW joints with the highest shear strength among all tested ultrasonic power levels (0 W, 300 W, and 600 W). Full article

In many areas such as the automotive, aircraft, and building industries, the high-strength aluminum alloy Al 7075 is frequently used due to its appropriate properties as a lightweight structural material. However, due to modest weldability, it is challenging to obtain high-quality welds with suitable mechanical properties, as cracks are generated while welding. Moreover, in order to avoid post-welding heat treatments and the use of complex welding equipment, in this paper the Al 7075 alloy is welded with MIG under longitudinal vibrations by using the Al 4043 alloy as filler material. As a consequence of strengthening the HAZ through precipitation, the mechanical and structural properties of the welded joints can be improved. These are investigated both under longitudinal forced vibrations at 50 Hz and without such vibrations. The results reveal improvements in terms of reducing the risk of hot cracking, obtaining a band structure free of porosity of the welds, improving the hardness of the welds under vibrations by 8.7% to 12.5%, and improving the tensile strength of the plates welded under vibrations by 12 to 15.5% in comparison to no vibrations. In relation to other welding procedures, the proposed procedure is more cost-effective and the weld quality is improved during the welding process. Full article