Microstructure, mechanical and corrosion properties of dissimilar friction stir welded aluminum alloys joints

2024 and 7075 aluminum alloys sheets of 5 mm thickness were used to conduct the friction stir butt welding tests by employing three welding speeds (60, 100 and 240 mm/min).The microstructure, mechanical properties and corrosion behavior of dissimilar friction stir welded 2024-7075 joints were studied by using electron backscatter diffraction (EBSD), hardness testing, tensile testing, scanning electron microscopy and polarization curves testing. The results show that the dynamical recrystallization occurs in the weld nugget to form fine equiaxed grains. The average grain size decreases from the shoulder region to the bottom region in the thickness direction, and the average grain size at different positions in the weld nugget decreases with the welding speed increasing. Different types of shear textures form at different locations in the weld nugget region of the dissimilar joint, and vary with the change of the welding speed. The hardness profile of the weld nugget zone shows a W type distribution trend, and its hardness value is lower than that of the base metals. The lower hardness value is located in the heat-affected zone. As the welding speed decreases, the hardness value of each zone shows a downward trend. The strength of the joint increases with the increase of the welding speed, and the welding efficiency reaches 90.3%. Comparing with the base metals, the weld nugget zone in the joint exhibits the worst corrosion resistance, mainly because of the significant galvanic corrosion in the weld nugget zone of the dissimilar weld joint, resulting in a higher corrosion current density. © 2019, Editorial Office of Systems Engineering and Electronics. All right reserved.