Microstructure and Mechanical Properties of AA 6061 and AA 7072 Friction Stir Spot Welds Using the Pinless Tool

AA 6061-T6 and AA 7072-T6 aluminum alloys were separately friction stir spot welded using a novel L-shaped grooves pinless tool. Mg–Si and Fe–Si–Al precipitates were found in the microstructure of AA 6061 joints and Mg–Si, Mg–Zn (η precipitates) and Al–Mg–Zn were the main precipitates in AA 7072 welds. It was observed that the retrogression-like process occurred in the case of AA 7072 welds. There was the optimum dwell time to obtain the strongest weld for each alloy. The hardness values were decreased in the stir zone for AA 6061 weld, while an increasing trend was observed in the case of AA 7072 stir zone. The relatively high strength joints were obtained using the novel pinless tool; the highest tensile-shear loads were 2277 N and 2539 N for AA 6061 (dwell time of 6 s) and AA 7072 (dwell time of 8 s) welds, respectively.