Microstructure and nanomechanical behavior of friction stir welded joint of 7055 aluminum alloy

In this paper, microstructure characterization of friction stir welding (FSW) joint of 7055-T6 aluminum alloy was performed via scanning electron microscope, electron backscatter diffraction, and transmission electron microscope technology. The nanomechanical behavior of FSW joint was systematically studied using nanoindentation technique. The relationship between microstructure and nanomechanical behavior was established and the nanohardness and microhardness were analyzed. The results show that FSW led to grain refinement of aluminum alloy and continuous dynamic recrystallization and geometric dynamic recrystallization were the primary mechanisms of grain refinement. The precipitated phase dissolved and coarsened during FSW, which led to a decrease in the microhardness of the joint. The nano-hardness of each zone of the joint displayed indentation size effect. The creep behavior at room temperature conformed to the Voigt model, and dislocation glide was the primary creep mechanism. The stir zone (SZ) and thermo-mechanically affected zone (TMAZ) had high nano-hardness and elastic modulus, while TMAZ and heat-affected zone (HAZ) had high creep resistance at room temperature. The nanomechanical behavior was mainly affected by precipitation in the grain interior.