Microhardness and Tensile Properties of Friction Stir Welded Joint of 2024 Aluminum Alloy at Different Welding Speeds

2024 aluminum alloy plate with thickness of 5 mm was welded by friction stir welding at different welding speeds (20-100 mm·min^-1). The microhardness and tensile properties of the welded joints were studied. The results show that the microhardness of the joint in the direction of perpendicular to the weld showed a W-shaped asymmetric distribution. The microhardness of the weld nugget zone was higher than that of the heat affected zone and the heat affected zone, but still lower than that of the base metal; the microhardness of the transition position between the heat affected zone and the thermo-mechanically affected zone was the lowest. With the increase of welding speed, the average microhardness of the weld nugget zone increased; the tensile strength and elongation of the welded joint increased first and then slightly decreased. When the welding speed was 80 mm· min^-1, the tensile strength and elongation both reached the maximum values of 347.2 MPa and 7.8%, respectively. The shear fracture of the joint occurred at the transition position between the heat affected zone and the thermo-mechanically affected zone, and the fractured position corresponded well with the position with the lowest hardness. The fracture mode of the joint was ductile fracture.