Abstract
Friction stir spot welding (FSSW) was applied to dissimilar lap joint between aluminum alloy sheet and mild steel sheet without formation of brittle intermetallic compound at the weld interface. A sufficient strength of the dissimilar joint was obtained by stirring aluminum alloy near the interface without inserting a welding tool to steel surface from the aluminum alloy side. Consequently, joint strength of FSSW was higher than that of resistance spot welds, and the all of FSSW joints showed a plug fracture through aluminum alloy parent sheet. Moreover, it was suggested that joint strength was related to area of stir zone at the weld interface. An oxide film was observed partially in the stir zone by sweeping up from the interface. No brittle intermetallic compound was observed at the weld interface. But only the thin amorphous layer of several nm in thickness including oxygen was found at the weld interface.
