Design, evolution, formation and effect mechanism of coupling distributed soft and hard micro-regions in Al–Zn–Mg–Cu–Fe alloys with high formability

Abstract

Here, we report the design, evolution, formation and effect mechanism of coupling distributed soft and hard micro-regions, and propose the mechanism of evading the strength-formability trade-off dilemma for Al–Zn–Mg–Cu alloys. The results show that the coupling distributed soft and hard micro-regions, i.e., spherical shell distribution of soft and hard micro-regions, can be formed based on the precise theoretical calculation and thermomechanical processing control. Simultaneously, a heterogeneous grain distribution of fine and coarse grains can be induced in the alloys, which results in the greatly improved average plasticity-strain ratio r to the value of 0.761. This value is much higher than those of the other 7xxx series Al alloys with a similar ultimate tensile strength. Based on the microstructure evolution, the forming mechanism of heterogeneous grain distribution was proposed. These findings shed light on new strategies for designing and developing high-strength and high-formability Al–Zn–Mg–Cu alloys and other Al alloys.