Effect of high Cu concentration on the mechanical property and precipitation behavior of Al–Mg–Zn-(Cu) crossover alloys

Al-Mg-Zn-(Cu) crossover alloys, embracing the advantages of traditional 5xxx and 7xxx series aluminum alloys, are being designed to achieve a better trade-off between ductility and achievable strength. In this study, we achieve an excellent strength–ductility combination in a high Cu-concentration Al-4.0Mg-3.0Zn-1.5Cu (wt.%) crossover alloy. The effect of high Cu concentration on its mechanical property and microstructure evolution was investigated in detail. Its yield strength increases by 80.5% without loss of ductility as compared to the Cu-free alloy. This is because, on one hand, introducing 1.5 wt.% Cu accelerates the precipitation kinetics of the nano-sized precipitates and increases the solid solution strengthening contribution, thus enhancing the yield strength. On the other hand, this Cu alloying improves the strain hardening ability of this alloy and its ductility by reducing the width of the precipitation free zone (PFZ), enhancing the forest dislocation strengthening contribution, and introducing slowly coarsening precipitates. The study demonstrates a simple but efficient strategy to significantly accelerate the age-hardening response and improve the strength without obvious loss of ductility for Al-Mg-Zn-(Cu) crossover alloys.