Friction Stir Spot Welding of Aluminum to Steel by Rotating Tool without Probe

Abstract

A friction stir spot welding process, in which a rotating tool without a probe was employed, was applied to a lap joint of aluminum plate to low carbon steel plate. The thicknesses of both plates were 0.5 mm. In this process, the rotating tool of 5 mm diameter, rotating at 18000 rpm, was plunged into the aluminum plate at a rate of 2 mm/s, and then kept at a maximum plunged depth of 0.05–0.35 mm for 0–2 s (dwell time). In the weld obtained by this process, a hole due to the impression of the penetrated tool probe was not formed, although a slight depression by the tool plunging remained. At tool plunge depths of 0.1 mm or over, it was possible to weld the two plates. The maximum tensile failure load of 454N was obtained at a plunge depth of 0.1 mm and a dwell time of 1.5s. Its joint was fractured at an almost constant load along the periphery of the depression, leaving a part of the aluminum plate on the steel plate surface. Based on the observation of the weld interface microstructure and metal flow of aluminum in the weld, controlling factors of the joint strength were discussed.