Effect of Press Amount on Microstructure and Mechanical Properties of Al-0.75Mg-0.75Si-0.8Cu Alloy Friction Stir Welded Joint

Al-0.75Mg-0.75Si-0.8Cu alloy was smelted and then subjected to homogenization, rolling, solid solution and aging treatment successively. Friction stir welding was carried out on the alloy under different press amounts (0.04, 0.08, 0.12, 0.16 mm), and the effects of press amount on microstructure, texture and mechanical properties of the joint were studied. The results show that with the increase of the press amount, in the nugget zone the grain size increased, the banded crystal was transformed to the equiaxed crystal, the proportion of the high angle grain boundary decreased first and then tended to be stable, and the proportion of the recrystallized grain decreased first and then increased slightly. Meanwhile, the $\overline{\text{A}}$ and C textures in the middle area of the nugget zone changed to the $\overline{\text{B}}$ texture due to the increase of plastic deformation. The lowest hardness of the joint under different press amounts appeared in the thermo-mechanically affected zone on advancing side. With the increase of the press amount, the hardness, tensile strength and elongation after fracture of the joint increased first and then decreased, all were lower than those of the base metal. When the press amount was 0.08 mm, the hardness, tensile strength and elongation after fracture were the largest, and there were small and dense dimples in the tensile fracture.