Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding (SSFSW) method. The results showed that using a pin with small shoulder could broaden the process window, and under a rotation speed of 2 000 r/min and welding speed of 30 mm/min, joint with smooth surface, small reduction in thickness and little inner defects was obtained. The weld nugget zone was approximately circular, which was a unique morphology for SSFSW. The heat-affected zone (HAZ) and thermo-mechanically affected zone (TMAZ) were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder. The fraction of high angle grain boundaries (HAGBs) exhibited a “W” shape along horizontal direction (from advancing side to retreating side), and the minimum value located at HAZ. The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%, respectively, with the joint efficiency of 68.3%. The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different regions of the joint. Microhardness distribution in the joint exhibited a “W” shape, and the difference along the thickness direction was negligible. The joint had strong stress corrosion cracking susceptibility, and the slow stain rate tensile strength was 139 MPa. Microcrack and Al₂O₃ particulates were observed at the fracture surface.