Microstructure evolution of thermo-mechanically affected zone in dissimilar AA2024/7075 joint produced by friction stir welding

In the present research, the microstructure characterization of the thermo-mechanically affected zone (TMAZ) in dissimilar FSW AA2024/7075 joint was systematically investigated. The results showed that many Cu-rich and Zn-rich constituent particles are generated in the TMAZ on the advancing side (AS-TMAZ) and the retreating side (RS-TMAZ), respectively. This mainly depends on the corresponding base materials (BMs) at the AS and RS. The precipitated particles are coarsened in the AS-TMAZ and RS-TMAZ compared to the corresponding BMs owing to the thermal cycle produced during FSW. Grain bending occurs in the TMAZ, and the degree of grain curvature in the RS-TMAZ are more pronounced than that in the AS-TMAZ. Many dislocations and sub-grains including a large number of LAGBs can be found in the AS-TMAZ and RS-TMAZ. The entire texture intensity is stronger in the AS-TMAZ and weaker in the RS-TMAZ as compared to the corresponding BMs. The original texture components are changed and some new shear components can be produced as a result of the severe shear deformation during FSW. The hardness value of the AS-TMAZ and RS-TMAZ is lower than that of the corresponding BMs due to the precipitated particles coarsening during FSW.