Effect of Zr, Cr and Pr additions on microstructures and properties of ultra-high strength Al–Zn–Mg–Cu alloys

The effect of Zr, Cr and Pr additions on the microstructures, mechanical properties and corrosion resistance of ultra-high strength Al–Zn–Mg–Cu alloy was investigated. By Zr, Cr and Pr adding to Al–Zn–Mg–Cu alloy, 10–20 nm spherical coherent dispersoids were formed in Al matrix and identified as Zn, Mg, Cu, Cr, Pr-containing A13Zr with cubic L12 structure. The dispersoids remarkably inhibited the recrystallization of Al matrix, and numerous fine subgrain boundaries were retained. Compared to the partial recrystallized Al–Zn–Mg–Cu–Zr alloy and full recrystallized Al–Zn–Mg–Cu–Cr–Pr alloy, the unrecrystallized Al–Zn–Mg–Cu–Zr–Cr–Pr alloy exhibited higher resistance to intergranular corrosion, exfoliation corrosion and stress corrosion with the improved strength, fracture toughness and ductility.