Effect of pre-aging process on microstructure and properties of 7075-T8 aluminium alloy

Abstract

The 7075 aluminium alloy was treated by combining pre-aging and thermomechanical treatment to obtain excellent comprehensive properties. The properties of the alloy were investigated by hardness, exfoliation corrosion, intergranular corrosion, and electrochemical corrosion test. The microstructure of the alloy was observed by transmission electron microscopy. Furthermore, the relationship between microstructure evolution and performance change was investigated. The results showed that the hardness and corrosion resistance of the alloy were improved after the combination of pre-aging and thermomechanical treatment. With the change in the pre-aging temperature, the microstructure of the alloy changed significantly. The matrix precipitates were numerous, fine, and uniformly distributed, which significantly improved the hardness of the alloy, resulting in a peak hardness of 195.2 HV. The grain boundary precipitates were rounded and independent, the distance between the precipitates became large, and the discontinuous distribution was very obvious, which destroyed the formation of corrosion channels, hindered the development of corrosion, and effectively improved the corrosion resistance of the alloy. The exfoliation corrosion rating was P. The minimum depth of intergranular corrosion was 29.3 µm. The self-corrosion current density and corrosion rate were the lowest, 0.0013 mA/cm2 and 0.0427 mm/a, respectively.