To investigate the mechanical properties and fracture behavior of Cold Metal Transfer (CMT) welded joints of die-cast aluminum alloys with different types of welding wires, tensile tests are carried out on two joint configurations, namely butt joint and lap joint. The results show that the wire grade exerts a significant effect on the ultimate tensile force, fracture displacement and fracture absorbed energy of butt welds. Overall, the joints fabricated with ER5356 and ER4047 wires exhibit better performance than those using ER4043 wire. For lap welds, the ultimate tensile force is less sensitive to wire types, while their fracture displacement and maximum fracture absorbed energy present considerable fluctuations.

To systematically investigate the microstructural evolution and mechanical property response of AZ41M magnesium alloy TIG welded joints, alternating-current TIG welding is employed to perform butt welding on AZ41M sheets with 3 mm-diameter AZ81 filler wire. Sound welds with uniform formation, free of apparent surface defects and achieving full penetration, are acquired under optimized process parameters. The microstructure and mechanical properties of the joints are systematically characterized using optical microscopy, room-temperature tensile testing, bending testing, and fatigue testing. The results demonstrate that the welded joint yields a yield strength of 124 MPa, an ultimate tensile strength of 231 MPa, and an elongation of 17.4%, with its strength reaching 89.9% of the base metal. The joint successfully passes 180° face-bend and root-bend tests, indicating favorable ductility. The fatigue limit of the joint is determined as 65.2 MPa. High-cycle fatigue cracks preferentially initiate at or near the specimen surface, and the fatigue crack propagation zone exhibits clear radial striation features.

Capacitor Discharge Welding (CDW) was utilized to perform projection welding between double-layer high-strength hot-formed steel and nuts. An orthogonal experimental design was adopted to systematically investigate the influence of various process parameters on the performance of the projection welding joints, with particular emphasis on nugget size and torque strength. Based on the experimental results, optimal welding parameters were identified through range analysis and comprehensive weighted scoring. The optimal conditions were determined as follows: electrode pressure of 0.3 MPa, welding time of 1.1 s, welding voltage of 320 V, and cooling time of 0.5 s. Under these parameters, the heat-affected zone (HAZ) on the nut side is subdivided into coarse-grain and fine-grain regions, with a microstructure primarily composed of equiaxed ferrite. On the hot-formed steel side, the HAZ consists of a fully quenched zone, a partially quenched zone, and a tempered zone. The fully quenched zone exhibits a coarse lamellar martensitic microstructure, whereas the partially quenched zone features a mixed microstructure comprising martensite, ferrite, and bainite. The tempered zone is predominantly constituted by tempered martensite. Three-dimensional fracture morphology analysis reveals that the fracture mode of the projection welding joint between the upper nut and the hot-formed steel is characterized by a ductile-brittle mixed fracture, while the fracture mode in the lower-layer hot-formed steel joints is primarily brittle in nature.

For the friction stir welding of 3 mm thick 6005A-T6 aluminum alloy in a lap joint configuration, this paper investigates the effects of varying pin lengths and lap positions on the performance of the welded joints. The results show that the internal quality of the lap joint is sound. When the length of the stirring needle is constant, the tensile load of the weld when the lap plate is on the back side is higher than that when the lap plate is on the forward side. However, the length of the stirring needle has a great influence on the metal flow state inside the butt joint. When the butt plate is located on the backward side, the hook defect is connected to the S line; when the butt plate is located on the forward side, the hook defect presents a hook shape along the welding core area and the boundary line of thermal influence; when the butt plate is located at a certain position and on the backward side, the hook defect is connected to the welding core area. The maximum breaking load of the weld is 28 592.9 N when the length of the stirring needle is 3 mm, and the minimum breaking load of the weld is 23 514.7 N when the length of the stirring needle is 5 mm.

Based on Simufact Forming software, the rivet die selection and performance analysis of Self-Piercing Riveting (SPR) joining between DC01 steel sheet and die-cast magnesium alloy AM50A are investigated. The results show that the trapezoidal die exhibits better crack resistance compared with the flat-bottom die and the spherical die. Focusing on the trapezoidal die, the simulation model obtained through iterative optimization accurately predicts the joint forming process and failure modes under cross-peel and tensile-shear loading conditions. Furthermore, the simulated load-displacement curves, peak load and absorbed energy are highly consistent with the experimental results. The "process simulation-performance prediction-experimental validation" research framework established in this study can effectively support the rivet die selection and optimization for steel-to-magnesium SPR process, where the simulation method holds core value in crack resistance analysis, failure mode study and joint performance prediction.

To investigate the mechanical properties and failure modes of Self-Piercing Riveted (SPR) joints between steel sheets of varying strength grades and THAS cast aluminum alloy, quasi-static comparative tests are conducted under different overlap configurations and loading conditions. The results indicate that sound SPR joint quality is achieved through appropriate process design and optimized rivet-die selection, with the minimum residual bottom thickness and left/right interlock values remaining within acceptable limits. For qualified SPR joints, the peak loads under cross-tension, combined shear-tension, cross-tension peeling, and lap-shear loading conditions all increase with rising steel sheet strength, while the dominant failure mode transitions progressively from steel-side failure to aluminum-side failure. Under cross-tension loading, the peak load follows a descending order: pure cross-tension, combined shear-tension, and cross-tension peeling. Additionally, the lap-shear strength of single-rivet joints with linear overlap exceeds that of spot-welded joints employing steel sheets of equivalent grade.

Taking aluminum alloy adhesive-bonded blind riveting hybrid joints as the research object, this paper investigates the shear mechanical properties of single/double lap double-rivet adhesive-bonded blind riveting joints with different adhesive layer thicknesses and rivet arrangements. The results show that regardless of transverse or longitudinal rivet arrangement, the failure sequence of the joints uniformly initiates with cohesive failure of the adhesive layer. The rivet arrangement has no effect on the second peak load corresponding to rivet failure, while the overall failure load of transversely arranged joints is higher than that of longitudinally arranged counterparts. For single lap double-rivet joints, pull-out failure of rivets follows; for double lap double-rivet joints, the middle aluminum alloy sheet of the specimen undergoes irregular fracture subsequently. Within the test scope, the adhesive layer thickness has no significant influence on the overall failure mode of the joints. The findings can provide experimental basis for the structural design and engineering application of aluminum alloy adhesive-bonded blind riveting hybrid joints applied to vehicle bodies.

To address the cracking problem during Self-Piercing riveting (SPR) on AlSi10MnMg die-cast aluminum shock towers, a combined experimental and numerical approach is employed to investigate crack initiation and propagation behavior. Optimization is conducted from 3 perspectives: the riveting process, material composition, and die-casting process. The results indicate that riveting cracking is induced by the tensile stress in the lower sheet and the compressive stress in the adjacent region, while the low elongation and porosity defects of the cast aluminum make it prone to crack initiation. A contoured riveting die reduces plastic deformation and tensile stress; Sr modification treatment optimizes the eutectic Si morphology and increases elongation; and optimizing the runner, overflow, and die temperature reduces casting defects, thereby lowering the cracking risk.

Taking the rare earth magnesium alloy as the research object, an organic-inorganic composite passivation film is prepared by using silane-modified trivalent chromium passivation solution. To investigate the effects of process parameters such as silane concentration and passivation time on the quality and performance of the film, micro-morphology, film thickness, adhesion strength, and neutral salt spray tests are conducted. To investigate the influences of process parameters such as silane concentration and passivation time on the quality and performance of the film, microscopic morphology, film thickness, adhesion force and neutral salt spray test are conducted. The results show that the synergistic mechanism between silane and trivalent chromium could effectively fill the defects of the film, improve the compactness, and thereby enhance the corrosion resistance. The silane concentration is a key factor influencing the density of the film. When the silane concentration is too low, the three-dimensional network structure formed through cross-linking could not fully fill the pores of the passivation film, resulting in limited protective effect; while a reasonable silane concentration is conducive to the formation of a dense and uniform passivation film, effectively blocking the corrosive medium. Compared with not adding silane, the annual corrosion rate of the sample decreases by 65.97% (0.211 mm/a), but the duration of the passivation treatment needs to be controlled to avoid the slight dissolution of the passivation film in the trivalent chromium passivation solution, which would subsequently reduce the protective performance.

The new automotive seat cushion is designed based on the optimization definition of seating comfort composition materials, to solve the challenge effectively of the balancing soft comfort and stable support, as well as the static comfort and dynamic comfort. A comprehensive evaluation of the seat cushion's static and dynamic seating comfort is carried out by means of a combination of objective testing and subjective ratings. The results indicates that the optimized design offers a wider and more soft support for the hips, flanks, and thighs accompanied by a pressure distribution aligning with the physiological characteristics of seated posture. In subjective evaluation,, all scores of optimized design are higher compared to the conventional design, Among them, the indicators of bottoming sensation and vertical vibration absorption increased from 6 and 7 points to 7.25 and 8 points, respectively, demonstrating significant improvement. The optimized design could balance soft comfort experience and stable support performance, achieving a synergistic improvement in both static and dynamic comfort. This design approach provides a reference for the optimization design and evaluation on seating comfort of automobile seats.