This study investigates the effect of welding speed on the microstructure and mechanical properties of pulsed laser lap-welded 0.2 mm 316L stainless steel sheets, commonly used in fuel cell bipolar plates. Welding speeds ranging from 6 to 26 mm/s were tested while other laser parameters remained constant. Results show that increasing welding speed reduces heat input, overlap factor, and weld dimensions. A transition from full to partial penetration occurs beyond 6 mm/s, with no visible heat-affected zone. The weld microstructure features columnar ferrite near fusion boundaries and globular ferrite in the center. Tensile–shear tests reveal that welds maintain higher strength than the base metal up to 22 mm/s, with all fractures occurring in the base material. An optimal speed range of 10–14 mm/s ensures defect-free joints with improved mechanical performance. These findings provide practical guidance for thin-gauge stainless steel welding in fuel cell applications.

Based on the orthogonal experimental design method, taking CP980 steel as the research object and the tensile sheer force of spot-welded joints as the evaluation index, the effect of different process parameters on the welding performance of resistance spot welding was studied with the extreme variance method. The results indicated that welding current had a significant effect on the shear force, followed by electrode pressure, while welding time had the least effect; the optimal welding parameter of the CP980 spot welded joint was that the welding time was 400 ms, the welding current was 9.5 kA, and the electrode pressure was 3.6 kN. The formation of lath martensite during solidification led to a higher hardness in the nugget region, reaching a maximum of 434 HV. The subcritical heat-affected zone formed a softened zone with an average hardness value of 299 HV as a result of welding thermal cycling.

H1000 stainless steel is defined as a nickel-saving austenitic stainless steel, characterized by high strength and high elongation. DP590 steel is widely used in the manufacturing of vehicle bodies. DP590 dual-phase steel is classified as a high-strength low-alloy steel, known for its high strength and good formability. To address issues such as nugget deviation, inhomogeneous mixing of the internal nugget microstructure, and interfacial fracture during tensile-shear testing in resistance spot-welded joints of these dissimilar materials, a unilateral magnetic-assisted resistance spot-welding process was proposed. The influence of the external magnetic field on various properties of the joint was systematically investigated. The results indicate that the application of an external magnetic field significantly enhances the strength of H1000/DP590 dissimilar spot-welded joints, with joint strength increasing by approximately 14% and energy absorption capacity improving by about 30%. These improvements are attributed to the electromagnetic stirring effect induced by the magnetic field, through which the effective nugget diameter was enlarged, the microstructure was homogenized, and the macroscopic morphology of the nugget was modified. As a result, the bonding area between the nugget and the base metal is expanded, and the fracture mode of the joint is shifted from interfacial failure to partial button failure, thereby enhancing the mechanical properties of the joint.

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.