Interfacial Microstructure and Tensile–Shear Properties of AA1060/SUS304 Dissimilar Sheet Joints Fabricated by Uniform-Pressure Electromagnetic Pulse Welding

Compared with single-turn coil magnetic pulse welding, magnetic pulse welding using a uniform-pressure electromagnetic actuator (UP-EMPW) can provide a larger area of uniform pressure and address issues such as low energy utilization efficiency and short coil lifespan. In this work, AA1060 aluminum sheets were joined to SUS304 stainless steel sheets by UP-EMPW. The effects of discharge voltage and initial gap on the interfacial microstructure and mechanical properties of the joints were investigated by optical microscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and tensile shear tests. Two distinct interface morphologies were observed: wavy interfaces and straight interfaces. Their formation was influenced by the combined effects of discharge voltage and initial gap. Microhardness measurements across the weld interface were further conducted to evaluate the local mechanical response and to help interpret the strengthening mechanisms associated with different interfacial features. The results showed that straight interfaces without a transition zone exhibited hardness values between those of the base materials, whereas wavy interfaces with a transition zone showed higher hardness values than both parent materials. Although these hardness data should be considered qualitative because of the limited indentation spacing, the overall trend suggests a stronger local strengthening effect at the wavy interface. The tensile shear tests indicated that the maximum load first increased and then decreased with increasing discharge voltage or initial gap. The highest joint performance within the investigated range was obtained at a discharge voltage of 9 kV and an initial gap of 1.5 mm, with a mean maximum tensile–shear load of 3288 ± 256 N and failure in the aluminum base material. The improved mechanical performance appeared to result from the combined effects of mechanical interlocking and metallurgical bonding associated with the wavy interface and transition zone. Fracture surface analysis further showed that base material fractures exhibited mixed ductile and brittle features, whereas pull-out failures were characterized by localized bonding and limited interfacial bonding.