Synergistic effect of gradient Zn content and multiscale particles on the mechanical properties of Al–Zn–Mg–Cu alloys with coupling distribution of coarse–fine grains

This study investigated the influence of graded Zn content on the evolution of precipitated and iron-rich phases and grain structure of the alloys, designed and developed the Al–8.0Zn–1.5Mg–1.5Cu–0.2Fe (wt%) alloy with high strength and formability. With the increase of Zn content, forming the coupling distribution of multiscale precipitates and iron-rich phases with a reasonable matching ratio and dispersion distribution characteristics is easy. This phenomenon induces the formation of cell-like structures with alternate distribution of coarse and fine grains, and the average plasticity–strain ratio (characterizing the formability) of the pre-aged alloy with a high strength is up to 0.708. Results reveal the evolution and influence mechanisms of multiscale second-phase particles and the corresponding high formability mechanism of the alloys. The developed coupling control process exhibits considerable potential, revealing remarkable improvements in the room temperature formability of high-strength Al–Zn–Mg–Cu alloys.