Effects of post-weld heat-treatment and second-welding on tensile properties of friction stir welded 7075-T651 aluminum alloy

8 nun thick 7075-T651 aluminum alloy rolled plate was friction stir welded, and the effects of post-weld heat-treatment and second-welding of the weld back on the tensile property were investigated. The results show that the single-welded sample is defect-free and the transverse strength of the weld is 71% of the base materials. However, a lazy "S" line appeared in the nugget zone as zigzag crack and discontinuous cavities after post-weld T6-treatment. With increasing solution temperature, the "S" line and abnormal grain growth became evident. After post-weld T6-treatment, the Vickers hardness of the weld was restored to the level of parent material, but the strength and elongation were significantly reduced due to the crack initiation and propagation along the "S" line. The tensile properties were greatly improved after second-welding of the weld back.