Abstract: Natural aging effect and effect of pre-aging treatment on the microstructure and mechanical properties of 7A20 aluminum alloy were investigated by means of OM, TEM, Vickers hardness tester and multifunctional tensile testing machine. The results indicate that the solution treated 7A20 aluminum alloy has obvious natural aging hardening effect, and the microhardness increases by 117.86% after natural aging for 12 days, from 56 HV0.5 to 122 HV0.5. After the pre-aging treatment at 120 ℃×10 min, the natural aging hardening increment is the lowest, reduced by 16 HV0.5 compared to the solution treated alloy. Simultaneously, this pre-aging treatment improves the baking hardening effect, the yield strength and tensile strength increase by 166 MPa and 51 MPa respectively, while the elongation decreases by 7%. Before the bake hardening process, the strengthening effect in the grains comes mainly from GP zones coherent with the matrix; and after the baking treatment, it comes from dispersed strengthening phase η′ with a size of less than 5 nm.

Key words: 7A20 aluminum alloy, natural aging, pre-aging, microstructure, properties