Microstructure evolution and mechanical properties of friction stir welded dissimilar metal joints of 1060 aluminum and AZ31B magnesium alloys

The grain structure, texture evolution and mechanical properties of friction stir welded dissimilar metal joints of 1060 aluminum and AZ31B magnesium alloys were studied by electron backscatter diffraction (EBSD). The results show that the proportion of low angle grain boundaries (LAGBs) and average grain size decrease gradually from heat affected zone (HAZ) to nugget zone (NZ). In HAZ, the grain structure is similar to that of the base metals, while dynamic recrystallization occurs in the thermo-mechanical affected zone (TMAZ), forming a microstructure in which coarse grains and fine equiaxed grains coexist. NZ is composed of uniform and fine equiaxed grains. The texture of HAZ is similar to that of base metals. The {001}〈100〉 recrystallized cubic texture is formed in the Al-side NZ. At the NZ center, the grain orientation of magnesium grains deflects from the 〈0001〉|| normal direction (ND) to 〈0001〉|| welding direction (WD), while at the Mg-side NZ, the orientation of grains is 〈0001〉|| transverse direction (TD). The tensile strength of the joint is 96.1 MPa and the elongation is 13.2%, reaching 95% of the tensile strength and 65% of the elongation of 1060 aluminum alloy base metal respectively. The material softening caused by the decrease of HAZ dislocation density on the aluminum side and the difference of grain size between HAZ and TMAZ on the Al-side jointly promote the fracture of the joint near the Al-side HAZ/TMAZ interface. © 2022, China Science Publishing & Media Ltd. All right reserved.