protrusion friction stir spot welding: the microstructure and mechanical properties of Al 6061 alloy

With the successful application of the protrusion spot friction stir welding technology to 2024 aluminum alloy and low carbon steel plate with a thickness of 1 mm , this technique was expanded to the spot welding of 1 mm thick 6061 aluminum alloy in this study. The effects of the tool dwell time (6, 12, 18 s) and plunging depth (0.1, 0.14 and 0.18 mm) were investigated on the microstructure and mechanical properties of samples. Surface appearance of the welding zone showed that the keyhole was not formed and the appearance of weld was relatively smooth. Microstructure and mechanical results indicated that the welding zone with uniform and refine structure due to dynamic recrystallization presents higher hardness and strength than base metal while can be affected by dwell time. Increasing the plunging depth increases the tensile strength and also decreases the thickness of the upper sheet.Fracture surfaces of the failed specimens present the shear fracture and the interfacial fracture.