Abstract
Friction stir spot welding (FSSW) is one of the solid state welding methods, and it is getting attention as a dissimilar metal joining method which does not require auxiliary materials. We have developed a new dissimilar material joining method—scrubbing refill FSSW (Sc-RFSSW)—, and Sc-RFSSW provides higher joint strength than conventional FSSW methods in joining the aluminum alloy and non-coated mild steel. This new method is based on the concept of rapid formation of a newly formed surface by the interaction of high-hardness tool with the surface of lower plate. In this study, the mechanical properties and metallurgical joining interface of an aluminum alloy and an ultra-high strength steel joint by Sc-RFSSW were investigated. It was found that the joint strength of Sc-RFSSW was higher than that of the conventional RFSSW. In addition, stop action tests were conducted to observe the formation of the newly formed surface of the steel plate, and finally the mechanism of the formation of newly formed surface was discussed.
