Precipitation behavior and mechanical properties of Al–Zn–Mg alloy with high Zn concentration

The effect of Mg content on the precipitation behavior and resultant mechanical properties of high Zn-content Al–Zn alloy was studied by adding Mg to Al–20Zn alloy. The dynamic precipitation of Zn and η phases occurred in the Al–Zn–Mg alloys during hot rolling. The Zn phase promoted the precipitation of the η phase, which increased in size with increasing Mg content. Mg addition led to the decomposition of Al–Zn supersaturated solid solution and the precipitation of the η′ phase during natural aging at room temperature. In addition to the η′ phase, the nano-sized Zn phase precipitated in high Zn-content Al–Zn–Mg alloy during artificial aging at 120 °C. The analysis of mechanical properties showed that 0.5 wt% Mg addition can enhance the strength of Al–20Zn alloy after rolling and heat treatments due to the presence of nano-sized η and η′ precipitates. However, when Mg content was increased to 1 wt%, the mechanical properties of the rolled and heat-treated Al–20Zn alloy deteriorated due to the complete decomposition of Al–Zn solid solution and extremely large amount of solute atoms. •Zn and η phases dynamic precipitated in the high-Zn-content Al–Zn–Mg alloys.•Zn phase promote the precipitation of η phase.•Mg addition led to the decomposition of Al–Zn solid solution at room temperature.•Zn and η′ phases precipitated in the high-Zn-content Al–Zn–Mg alloys during aging.•The mechanical properties of high-Zn-content Al–Zn–Mg alloys were significantly affected by the precipitation behavior.