Effect of Two-Step Pre-aging on Precipitation Kinetic and Microstructure Evolution of 6A16 Aluminum Alloy

A two-step pre-aging treatment of 6A16 aluminum was designed in this paper. The mechanical properties were tested. The microstructure was characterized using DSC and TEM. The precipitation kinetic of strengthening phase was calculated. The results show that after (550 ℃, 5 min solid solution) + (100 ℃, 5 min + 180 ℃, 5 min) (multi-step pre-aging) heat treatment, the yield strength of the 6A16 aluminum alloy is 150 MPa, elongation of 24.4%, and the bake hardenability value is 114 MPa after paint-bake treatment. According to the calculation, the precipitation activation energy of β″ phase for the alloy is lower than that of T4 processed, which is 62.24 and 97.72 kJ/mol respectively. While the secondary aging temperature is 180 ℃ and 200 ℃, which is beneficial to the precipitation of precipitates in low temperature paint process. The multi-step pre-aging treatment could enhance the nucleation rate of GP zones when the secondary aging temperature is higher than 180℃, and promote the precipitation of effective β″ strengthening phase during paint-bake treatment, which the rapid aging response will be realized during the paint baking.