Cold Forge Spot-bonding of High Tensile Strength Steel and Aluminum Alloy Sheets

Abstract

Recently automobile components need to have various characteristics that are hard to be fulfilled using a single material for satisfying the several demands like weight saving, cost cutting and crash safety with trade-off relationship. Thus bonding or joining methods of dissimilar materials are necessary. However it is difficult to weld steel and aluminum together. Therefore the authors developed an alternative solid phase bonding method “spot-bonding”. In this method, the plastic deformation by cold forging would enable metallic bonding of two dissimilar metals. In this study, this method was applied to bonding of 590MPa-class high tensile strength steel and A2017P aluminum alloy sheets. The joint strength was measured by cross tension testing. When the amount of punch indentation is increased, the joint strength became higher. With the same depth of punch indentation as the total thickness, the joint was broken in the steel base metal blank but not at the interface. Finite element analysis was performed in order to consider the deformation behavior during the bonding process. The parameters on the bonding interface such as surface expansion ratio, surface pressure and relative slippage of two blanks became larger with increase in amount of punch indentation. Furthermore, the bonded region was predicted by calculating the total friction work and the evaluation factor of real contact area that depended on surface expansion and surface pressure.