Effect of pre-strain and two-step aging on microstructure and stress corrosion cracking of 7050 alloy

A novel heat treatment procedure that combines the pre-strain with a two-step aging was proposed to improve both the strength and stress corrosion cracking (SCC) resistance of the high strength 7050 aluminum alloy. The heat treatment included a post-quenching pre-strain of 5%, a high-temperature aging at 200 °C for several minutes, and a subsequent low-temperature aging at 120 °C for 24 h. The yield strength of the samples aged at 200 °C for 0.5 and 1 min was higher than that of the T6 sample. The SCC resistance of these samples was improved compared to the T6 sample, due to the enlargement in the size and the inter-particle distance of the grain boundaries precipitates and the decreases in the number of the GP zone. Especially, the sample aged at 200 °C for 5 min exhibited a similar SCC resistance and much higher elongation compared the T76 sample.