Influence of solution treatment on microstructures and mechanical properties of a naturally-aged Al–27Zn–1.5Mg–1.2Cu–0.08Zr aluminum alloy

Solution treatment and natural aging have been carried out to enhance the mechanical properties of a high-Zn aluminum alloy (Al–27Zn–1.5Mg–1.2Cu–0.08Zr) produced by melt spinning and extrusion. The studies show that the as-extruded alloy contains lots of Zn particles, Zn-rich η-MgZn2 particles at grain boundaries and oxidation films at ribbon interfaces. The Zn particles and Zn-rich η-phases can be fully dissolved at 370 °C and 450 °C respectively. However, when solution temperature is higher than 400 °C, the brittle oxide films are difficult to accommodate the plastic strains caused by thermal contraction during quenching, which may result in over-heating and quench cracking. The optimized solution temperature for the high-Zn aluminum alloy is 400 °C. The solution-treated alloys reveal a strong naturally age hardening. Both η′-phase and GP-zones are the main hardening phases for the naturally peak-aged alloy solution-treated at 400 °C, whereas GP-zones exist as the main hardening phase for the alloys solution-treated at 350 °C. Naturally peak-aged alloy solution-treated at 400 °C shows the highest strength and elongation among all of the experimental alloys. Its superior strength is mainly due to its higher-density of dispersed nano-sized precipitates and higher η′-phase percentage. •High-Zn Al alloy contains high-density Zn, rich-Zn η-MgZn2 and oxidation ribbon interfaces.•Optimized solution temperature for high-Zn Al alloy is 400 °C, otherwise higher temperature can result in over-heat and quench cracking.•High-Zn Al alloy shows a strong naturally aging hardening.•Main hardening phases for the alloy solution-treated at 400 °C are η′-phase and GP-zones, whereas the one for the rest experimental alloys is GP-zones.