Effect of Cu content and Zn/Mg ratio on microstructure and mechanical properties of Al–Zn–Mg–Cu alloys

Al–Zn–Mg–Cu alloys were fabricated with water-cooled copper casting. The microstructure of the alloys was characterized by electron probe microanalysis (EPMA), scanning electron microscope (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). The mechanical properties were studied with by tensile and hardness tests. The results showed an enhanced effect of solid solution strengthening and precipitation strengthening with increased Cu content. The distribution spacing of the grain boundary precipitates (GBPs) increased, but the width of the precipitate-free zone (PFZ) decreased. The process enhanced the strength and plasticity of the alloy. The impact of precipitation strengthening decreased and the grain size and width of the PFZ decreased as the Zn/Mg ratio increased. Thus, the strength of the alloy decreased and its plasticity increased with increasing Zn/Mg ratios.