The effect of impulses on precipitation behavior in 7075-T6 aluminum alloy joint by Impulse Friction Stir Welding

Abstract

Joining procedure for aluminum alloy 7075–T6 (AlZnMgCu1.5) sheets was realized by Impulse Friction Stir Welding (IFSW) with different impulse frequencies. The additional mechanical impulses during IFSW enhance the forging action of the tool, resulting in the weld microstructure modification. The microstructural evolution in different zones of the weld was studied, focusing on the strengthening precipitation behavior of the welded joint as well as the overall mechanical properties. The results illustrate that the application of impulses during IFSW accelerates the reprecipitation and dynamic recrystallization processes, which lead to the formation of strengthening precipitates and the homogeneous grain microstructure, respectively, in the SZ. HAZ of the welds obtained by the FSW and IFSW represent dislocation free grains interior. The precipitation content in the HAZ of the welds obtained by conventional FSW and IFSW is completely different. The HAZ of the weld obtained by conventional FSW represent high concentration of stable η phase. Conversely, high concentrations of heat sensitive phase - η' precipitates - were found in the HAZ microstructure of the joints obtained by IFSW.