Effect of processing parameters on mechanical properties of aluminum alloy joints welded by friction stir welding

The butt-joints of AA1060, AA2024 and AA6061 plate with 4 mm thickness were fabricated by friction stir welding in this study. The microstructure in different zones and the fracture morphology of joints were analyzed with OM and SEM, and the tensile strength and microhardness of joints were measured. The results indicate that the finest grain and the highest microhardness appeared in nugget zone, while the coarse grain and the lowest microhardness was in the heat affected zone. With the increase of welding velocity and rotation speed of tool, the tensile strength of joint increases to a maximum, and then decreases gradually. The tensile strength of the joint welded with optimized parameters is related linearly to the strength of basic metals. The dimple morphologies are observed in the fracture surface of joints broken down from the heat affected zone, which is resulted from the coarse structure and the segregation of second phase in the heat affected zone.