Microstructural evolution of nanostructure 7075 aluminum alloy during isothermal annealing

This work focuses on structural changes of nanostructure 7075 aluminum alloy (Al7075) during isothermal annealing. Nanostructured Al7075 was synthesized by mechanical alloying. The produced structure was isothermally heat-treated at 125–500 °C for 1–3 h under argon atmosphere. The as-milled and annealed powders were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that after 15 h of milling, an Al–Zn–Mg–Cu supersaturated solid solution with a grain size of 35 nm was obtained. By increasing the milling time up to 15 h, the MgZn phase precipitated from supersaturated solid solution. Large variety of precipitants including MgZn, MgZn2 (at temperatures range between 200 and 400 °C), AlCuMg and Al2Cu (at temperatures range between 300 and 500 °C) were formed during isothermal annealing.