Microstructure evolution and fracture behavior of dissimilar friction stir welding of 1060Al alloy to AZ31B Mg alloy

Abstract

In this paper, the microstructure evolution and fracture behavior of 1060 Al/AZ31B Mg dissimilar friction stir welded joints were investigated. Experimental results showed that dynamic recrystallization occurred in the nugget zone (NZ) and thermo-mechanically affected zone (TMAZ), and the grains were considerably refined. As the welding speed increased, the percentage of high angle grain boundaries (HAGBs) and the degree of recrystallization in the NZ gradually decreased, while the percentage of HAGBs and the degree of recrystallization in the Mg-side TMAZ first increased and then decreased. The NZ and Mg-side TMAZ possessed a strong {0001} basal texture, and the texture strength first increased and then decreased with increasing welding speed. When V = 30, 110, and 190 mm/min, the tensile strengths of the joints were 74 ± 2.2, 93 ± 3.3, and 80 ± 1.2 MPa, respectively. The joints showed two fracture modes: the joint fractured along the Mg-side TMAZ/NZ interface (mode I); the joint failed from the bottom of NZ and then fractured along the middle region between the NZ and Mg-side TMAZ (mode II). The grain size, texture distribution, and local dislocation concentration affected the fracture behavior of the joints. • The evolution of microstructure and fracture behavior of Al/Mg dissimilar FSWed joints were studied by EBSD. • Two fracture modes of the joints were found and discussed. • The fracture mechanism of the joints at different welding speeds was clarified.