Effects of heat treatment processes on the mechanical properties, microstructure evolution, and strengthening mechanisms of Al–Mg–Zn–Cu alloy

In this study, the mechanical properties and strengthening mechanisms resulting from the evolution of microstructure in an Al-4.39Mg-2.78Zn-0.42Cu (wt%) alloy were investigated through various heat treatment processes. Compared with the conventional T6 process, both the final thermomechanical treatment (FTMT) and the T6+deformation (T6D) process were found to significantly increase the strength of the alloy. In FTMT and T6D treated alloys, the distribution of nano-sized T-Mg32(Al, Zn, Cu)49 phase and dislocations were observed throughout the microstructure. Furthermore, the FTMT process led to a decrease in the solid solution amount of Mg atoms in the alloy, resulting in an improvement of the Portevin-Le Chatelier (PLC) effect. The increase in yield strength of the FTMT-treated and T6D-treated alloys was attributed to the combined effects of enhanced precipitation strengthening and introduced dislocation strengthening. However, the contributions of grain boundary strengthening and solid solution strengthening remained relatively unchanged. This study presents a strategy for producing Al–Mg–Zn–Cu alloys with excellent mechanical performance by manipulating their microstructure and strengthening mechanisms.