Effect of non-isothermal retrogression and re-aging treatment on microstructure evolution and mechanical properties of Al–Zn–Mg–Cu alloy

Abstract

The mechanical properties of rolled 7075 aluminum alloy treated by non-isothermal retrogression and re-aging can exceed the traditional peak aging (T6) and isothermal retrogression and re-aging. After non-isothermal retrogression and re-aging (NIA 180/60) treatment, compared with the T6 state alloy, the alloy has obvious grain boundary precipitate-free zone, and the tensile strength is increased from 558 ± 1.2 MPa to 611 ± 1 MPa. The main mechanism leading to the increase of mechanical properties is precipitation strengthening, followed by grain boundary strengthening, which is not related to crystal orientation, dislocation strengthening and solid solution strengthening. During the non-isothermal retrogression and re-aging treatment, the partial dissolution of the existing precipitates (GP zone and η′ phase), the growth of the remaining precipitates and the precipitation of new η′ phase, as well as the secondary precipitation in the re-aging stage, lead to the increase of the size and density of the intragranular precipitates compared with the T6 state alloy, and the maximum precipitation strengthening effect is obtained. This paper also discusses the relationship between performance changes and microstructure, which can provide a reference for optimizing the regression re-aging process.

Keywords

• Al-Zn-Mg-Cu alloy
• Non-isothermal retrogression
• Mechanical property
• Strengthening mechanism