In this research, the distribution of the hardness and residual stress in the joining of three layers of explosion-welded Al1050/Al2024/Al1050 aluminum alloy sheets, which were friction stir welded, was investigated. The rotational speed and traverse speed parameters were determined by trial and error in order to achieve a weld without cracks and holes. Due to the selection of steel tools with a shoulder diameter of 20 mm and an incomplete conical pin with a large diameter of 4 mm, only the desired welds were made at a rotational speed of 710 rpm, a forward speed of 16 mm/min and 20 mm/min, a rotational speed of 1120 rpm, and a transverse speed of 20 mm/min. In other cases, the welding has defects or low surface quality. To check the residual stress, the contour method, which is one of the new destructive methods, was used.
By examining the obtained results, it was found that the residual stress in the center of the part (welded zone) was tensile, and it was compressive at the edges of the part along the thickness. Considering the yield strength of the base metal, which was about 205 MPa, and the highest value of residual stress, which was about 35 MPa, at a rotational speed of 710 rpm with a transverse speed of 20 mm/min, the highest residual stress was about 17% of the yield strength of the base metal.