The softening effect of heat-treated strengthened Al–Zn–Mg alloy in welding process

Weld joint softening occurs during the welding process of heat-treatable aluminum alloys and strongly influences the mechanical properties. In this work, the softening of heat-treated Al–Zn–Mg alloy was studied in the multipass welding process. By Gleeble-3500 thermal–mechanical simulator, the heat treatment and tensile test with welding thermal cycles were carried out to simulate the microstructure evolution and mechanical softening during multipass welding. After that, the softening mechanism of the HAZ was analyzed by microstructure analysis. The results indicate that the heat-treated Al–Zn–Mg alloy exhibited obvious softening after several thermal cycles with peak temperature higher than 200[Formula: see text]C, and this phenomenon is worse with increasing peak temperature. Based on the microstructure analysis, it was found that the reinforcement phase changes according to the applied thermal cycles, which strongly affects the strength of Al–Zn–Mg alloys.