Effect of Zr, Er and Cr additions on microstructures and properties of Al–Zn–Mg–Cu alloys

The effects of Zr, Er and Cr additions on the microstructures, mechanical properties and corrosion resistance of Al–Zn–Mg–Cu alloy were investigated. The combined additions of Zr, Er and Cr to Al–Zn–Mg–Cu alloy led to the formation of coherent Zn, Mg, Cu, Cr-containing Al3(Zr, Er). These 15–25 nm secondary precipitates 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, the unrecrystallized Al–Zn–Mg–Cu–Zr–Er–Cr alloy exhibited higher resistance to intergranular corrosion and stress corrosion with the improved mechanical properties and fracture toughness. The synergetic effects of Zr, Er and Cr on the precipitates, recrystallization and corrosion resistance of ultra-high strength Al–Zn–Mg–Cu alloys have been discussed.