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 contribution 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 intermetallic compound (IMC) is formed at the joining interface. Therefore, the strength of the joint decreases as the IMC becomes thicker. In this study, the joint surface shape was changed to improve the tensile shear strength (TSS). Specifucally, a groove was machined into the steel sheets and resistance spot welded to aluminum alloy sheets. Cross sectional observations of the resulting joints confirmed that molten aluminum successfully flowed into the groove, creating a convex interface shape. Tensile shear tests were conducted to evaluate mechanical performance. The results showed that the TSS was improved in joint using R shaped electrodes and a groove outer diameter of 8.0 mm. This is thought to be due to the change in fracture behavior caused by the convex interface shape.
KUBO et al. (Wed,) studied this question.
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