Quantitative analysis of grain structure and texture evolution of dissimilar AA2024/7075 joints manufactured by friction stir welding

Abstract

Friction stir welding (FSW) can successfully join aluminum alloys that are difficult to weld. However, FSW causes texture inhomogeneity in the nugget zone (NZ), which may affect the integrality of joints. Thus, a quantitative study on the grain structure and texture evolution of the NZ in dissimilar AA2024 and AA7075 joints at three welding speeds was performed via electron backscatter diffraction. The results showed that dynamic recrystallization in the NZ generates fine equiaxed grains instead of elongated grain microstructure in base materials. The average grain size and recrystallization degree are reduced with the increment in welding speed. Different kinds of shear texture components are formed and the shear textures are significantly decreased from 66.4% to 12.1% with the decrease in welding speed from 240 mm/min to 60 mm/min. The variation in grain structure and shear textures depends largely upon the welding heat inputs at different welding speeds. The research contributes to understanding the mechanism of microstructure homogenization in FSW joints and further optimizing welding process for engineering application.