Synergistic effect of gradient Zn content and multi-scale particles on the mechanical properties of Al-Zn-Mg-Cu alloys with coupling distribution of coarse / fine grains

The influence of graded Zn content on the evolution of precipitated and iron-rich phases and grain structure of the alloys was investigated, and the Al-8.0Zn-1.5Mg-1.5Cu-0.2Fe (wt.%) alloy with high strength and high formability was designed and developed. With the increase of Zn content, it is easier to form the coupling distribution of multi-scale precipitates and iron-rich phases with a reasonable matching ratio and dispersion distribution characteristics, which can induce the formation of cell-like structure with alternate distribution of coarse and fine grains, and the average plasticity-strain ratio r value (characterizing the formability) of the pre-aged alloy with a high strength is up to 0.708. Finally, the evolution and influence mechanisms of multi-scale second-phase particles, as well as the corresponding high formability mechanism of the alloys were revealed. The developed coupling control process exhibits great potential and can significantly improve the room temperature formability of high strength Al-Zn-Mg-Cu alloys.