Microstructure and Mechanical Properties of 2A14-T4 Alloy T-Joint Connected by Stationary Shoulder Friction Stir Welding

In this study, the evolution of microstructure and mechanical properties of the 2A14-T4 aluminum alloy stationary shoulder friction stir welding (SSFSW) of a T-joint was analyzed. The results showed that the weld surface had almost no thinning, little flashes, and no external defects. Equiaxed crystal grains were formed in the weld nugget zone (WNZ) after full dynamic recrystallization, while incomplete dynamic recrystallization occurred in the thermomechanically affected zone (TMAZ), and the grains grew in the TMAZ. The microstructure of the heat-affected zone (HAZ) coarsened to a certain extent under the action of high temperature. The hardness distribution in the direction of the bottom plate of the joint presented a W-type curve on the whole, and the hardness distribution in the direction of the rib plate presented an N-type curve on the whole. The lowest point of hardness usually appeared at the junction of the first and second welds, as well as on the HAZ-TMAZ interface. The distribution of residual stresses in the SSFSW T-joint was uniform, while the thermal-mechanical rolling effects of the second weld led to the reduction of residual stresses in the first weld.