Microstructures and mechanical properties of 6061-T6 aluminum alloy welded by stationary shoulder friction stir welding process

6061-T6 aluminum alloy butt joints were successfully obtained by stationary shoulder friction stir welding SSFSW process using the self-developed tool system. Welding surfaces, microstructures, hardness profiles and tensile properties of the obtained joints were measured and studied, respectively. The results show that the obtained joints by SSFSW process had nice-looking appearances and smooth surfaces. Compared with conventional FSW, the phenomenon of the weld thickness reduction was almost eliminated. The microstructures of SSFSW joints were also significantly different. The thermomechanically affected zone was quite narrow, whose width was only a few hundred micrometers. The hardness profiles of obtained joints presented "W" shape. At the tool rotation speed of 1 000 rpm and the welding speed of 200mm/min, both the tensile strength and the elongation reached the maximum, which were up to 71.5% and 44.6% of the base material, respectively. All the joints were fractured at the heat affected zone, which was the weakest region.