Concurrent Improvement of strength, formability and SCC resistance of Al-Zn-Mg-Cu alloy by hot stamping after rapid heating and re-aging on paint baking treatment

In this study, the combined application of rapid heating for hot stamping and the subsequent re-aging during a paint baking treatment was newly developed for T6-tempered A7075 Al-Zn-Mg-Cu alloy sheets. From a systematic investigation, rapid heating to 255-260 ℃ and short-time holding for ~120 s was found to give the best combination of formability, hardness and stress corrosion cracking (SCC) resistance of the final products. In particular, re-aging treatment at 170 ℃ for 1.2 ks was well exploited not only for further improvement of SCC resistance but also for rebound of the decreased hardness by rapid heating. Therefore, the developed three-step heat treatment is regarded as a promising approach to producing high-strength, easily formable and corrosion-resistant Al-Zn-Mg-Cu alloy parts for automobiles.