Modifying the microstructure and stress distribution of crossover Al-Mg-Zn alloy for regulating stress corrosion cracking via retrogression and re-aging treatment

Abstract

For next-generation high-performance Al alloys, stress corrosion cracking (SCC) under the combined action of anodic dissolution and hydrogen embrittlement has been a long-standing problem. Herein, a novel SCC-resistant Al alloy design strategy that maintains high strength by optimizing the microstructure and microstress distribution is proposed and developed. Results demonstrated that stress corrosion cracks sprouted and expanded along stress concentration regions. In a T-phase strengthened crossover Al–5.0Mg–4.0Zn alloy, minimal stress concentrations at the grain and phase boundary improved the SCC resistance by high-temperature retrogression and re-aging treatments. Compared with the T6 alloy, the high-temperature retrogression RRA435 °C alloy reduced stress concentration by 36.7% and decreased the diffusion rate of H atoms by 81 folds. The improved SCC resistance was primarily attributed to the reduced diffusion coefficient of hydrogen because of the minimal stress concentrations.