Enhancing Stress Corrosion Cracking Resistance of Low Cu-Containing Al-Zn-Mg-Cu Alloys by Aging Treatment Control

The 7085 aluminum alloy with a low Cu content is an important lightweight structural material in the aerospace field due to its advantages of low density, high specific strength, and high hardenability. However, like other high-strength Al-Zn-Mg-Cu alloys, this alloy is susceptible to stress corrosion cracking (SCC). Additionally, the lower Cu content may increase its tendency toward SCC, potentially impacting the safe use of this alloy. Therefore, this study investigated the effects of aging treatment processes on the mechanical properties and SCC resistance of 7085 aluminum alloy. And the factors affecting the properties of the alloy were analyzed by optical microscope (OM), scanning transmission electron microscope (STEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. The results indicated that increasing the secondary aging temperature and adding a tertiary aging step can significantly reduce the alloy's susceptibility to SCC while meeting the mechanical performance requirements. The reduced SCC sensitivity was mainly attributed to the increased spacing of grain boundary precipitates, a wider precipitate-free zone at the grain boundaries, and a higher Cu content in the grain boundary precipitates.