The worsening of environmental issues in recent years has prompted the automotive industry to extensively explore the adoption of multi-material structures, particularly those combining steel and aluminum alloys. This strategic shift aims to achieve significant reductions in overall vehicle weight, thereby contributing to enhanced fuel efficiency and decreased emissions. However, when resistance spot welding, a common and widely utilized joining method in the automotive industry, is applied to steel and aluminum alloy, it is known that the peel strength of the joint decreases due to the intermetallic compounds formed at the joint interface. Therefore, in previous studies, the peel strength of the joint was improved by changing the interface shape to a rectangular shape through welding performed after machining. The reason for this is thought to be the change in the direction of the intermetallic compound formation on the groove sides. On the other hand, there is a possibility that further improvements in joint strength can be achieved by optimizing the electrode shape on the aluminum side. In this study, the effects of the shape of the aluminum side indentation on the joint strength of the joints with the rectangular interface were investigated. Specifically, a groove was machined into the steel sheets and resistance spot welded to aluminum alloy sheets. When performing the welding, by changing the electrode shape and tip curvature on the aluminum side, the indentation shape was varied. Cross tension tests and tensile shear tests were conducted on the joints made this way. The results showed that changes in the shape of the aluminum side indentation affected the strength of the joint. This is thought to be because the change in the indentation shape on the aluminum side affected the fracture morphology.
KUBO et al. (Thu,) studied this question.