Effect of Interrupted Aging–Retrogression Re-Aging Treatment on the Microstructure and Properties of Al-Zn-Mg-Cu Alloy.

This study aims to investigate the microstructure and properties of Al-Zn-Mg-Cu alloy that is subjected to a coupled aging treatment, interrupted aging (T6I4) and retrogression and re-aging (RRA). For this purpose, the properties were systematically investigated through the tests of Vickers hardness, tension, and intergranular corrosion. The matrix precipitates were analyzed by transmission electron microscopy. According to the experimental results, the alloy treated by T6I4-RRA was improved by 37% in elongation with the loss of 2% in strength compared to that treated by peak aging (T6). In addition, the corrosion depth of the alloy treated by coupled aging decreased by 40% compared to that of the T6-aged material. According to the microstructure investigations, finer precipitates were formed in the T6I4-RRA-aged alloy, accompanied with intermittent grain boundary precipitates and appropriate precipitate-free zones. Importantly, this peculiar microstructure contributes to resolving the contradiction between strength properties and corrosion resistance of Al-Zn-Mg-Cu alloy. [ABSTRACT FROM AUTHOR]