Effect of Pre-aging - Warm Forming Process Parameters on Microstructure and Properties of 7075 Aluminum Alloy

The 7075 aluminum alloy was pre-aged and warm formed at different pre-aging temperatures (85, 100, 120 ℃) for different pre-aging times (0–32 h) and forming temperatures (150, 200, 250, 300 ℃). The effect of process parameters on the microstructure and properties of alloy was studied. The optimum process parameters were determined. The results show that with the extension of pre-aging time, the grain size of 7075 aluminum alloy had no obvious change, the amount of precipitated phase increased, and the hardness and strength increased first and then decreased. Compared with those at pre-aging temperature of 100, 120 ℃, the number and the size of precipitated phases were smaller, the hardness and strength were larger, and the percentage elongation after fracture was smaller at the pre-aging temperature of 85 ℃. The hardness and strength decreased with the increase of warm forming temperature. The optimum pre-aging-warm forming process parameters were listed as follows: pre-aging temperature of 85 ℃, pre-aging time of 24 h, and warm forming temperature of 150 ℃. At this time, the alloy had the best comprehensive properties, which had the tensile strength and percentage elongation after fracture were 95% and 163% of those of the 7075-T6 aluminum alloy, respectively. Baking at 180 ℃ for 30 min after forming could improve the strength and reduce the ductility.