Effect of retrogression treatments on microstructure, hardness and corrosion behaviors of aluminum alloy 7085

The microstructure, hardness and corrosion resistance of aluminum alloy 7085 after different retrogression and re-aging (RRA) treatments were investigated. The results showed that the properties of alloy 7085 are sensitive to the temperature and dwell time of the retrogression treatment. Desirable mechanical property and corrosion resistance can be obtained for the alloy pre-aged at 120 °C for 24 h, followed by a retrogression at 160 °C for 1.5 h and re-aging at 120 °C for 24 h. After the optimized RRA treatment, the hardness of alloy 7085 is improved by 10.2% as compared with the peak-aged one, which is mainly due to the distribution of dispersed rod-like η′ precipitates in the matrix; while the improved corrosion resistance is mainly attributed to the discrete and coarse η phase with higher Cu content, and narrow precipitate-free zone about 45–50 nm in width along the grain boundaries.