Microstructural evolution of Al–Zn–Mg–Cu–(Sc) alloy during hot extrusion and heat treatments

The microstructural evolution during hot extrusion and post heat treatment was investigated for two kind of Al–Zn–Mg–Cu–(Sc) alloy and AA7075. The microstructure of as-extruded bar is mainly comprised of recovered structure for all alloys, however, different restoration processes are observed during post heat treatment. For AA7075 and S1, which contains 0.1% Sc with relatively higher Zn and Cu content than S2, recovery still proceeds during the heat treatment, while the recrystallization becomes main restoration process during the heat treatment for S2. The differences in abnormal grain growth and hardening behavior between S1, AA7075 and S2 during the heat treatment are discussed in connection with the restoration processes and resultant microstructures.