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

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 eta-MgZn2 particles at grain boundaries and oxidation films at ribbon interfaces. The Zn particles and Zn-rich eta-phases can be fully dissolved at 370 degrees C and 450 degrees C respectively. However, when solution temperature is higher than 400 degrees 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 degrees C. The solution-treated alloys reveal a strong naturally age hardening. Both eta'-phase and GP-zones are the main hardening phases for the naturally peak-aged alloy solution-treated at 400 degrees C, whereas GP-zones exist as the main hardening phase for the alloys solution-treated at 350 degrees C. Naturally peak-aged alloy solution-treated at 400 degrees 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 eta'-phase percentage.