Influence of aging treatment on the microstructure and corrosion properties of Al-Zn-Mg-Cu-Zr-Er aluminum alloy

The influence of T6, T74, RRA aging treatment on microstructure, mechanical properties and corrosion properties of Al-Zn-Mg-Cu-Zr-Er aluminum alloy has been investigated by exfoliation corrosion, polarization curve, electrical conductivity, mechanical properties testing and TEM microstructure analysis. The results show that the alloy had the highest strength and toughness, but was susceptible to corrosion under T6 aging treatment(σ_b:663.5 Mpa; σ_0.2:625.4 MPa; δ:12.46 %). Compared with T6 aging treatment, the alloy had the best corrosion resistance with sacrificing the strength under T74 aging treatment(σ_b:640.2 MPa; σ_0.2:621.3 MPa; δ:11.34 %). Although the strength and toughness of RRA aging treatment(σ_b:657.8 MPa; σ_0.2:628.8 Mpa; δ:11.98 %)were slightly lower than T6 aging treatment, but it improved corrosion resistance obviously and had the excellent comprehensive performance. The strength and corrosion resistance of the alloy are related to matrix precipitates (η′) and grain boundary precipitates (η), respectively. A large amount of tiny η′ phase distributed more uniform and dispersed in matrix, the strength of the alloy is higher. The thick η phase distributed more discontinuous in the grain boundary, the corrosion resistance of the alloy is more beneficial, which is consistent with the physicochemical properties of η′ phase and η phase of the first principle.