Microstructure and properties of Al-11.0Zn-3.1 Mg-1.22Cu-0.1Sr-0.2Zr-0.1Ti-0.45Ce with strength over 800 MPa under interrupted aging

This article investigated the effect of interrupted aging (T6I4) on the microstructure and properties of an ultra-high strength Al-Zn-Mg-Cu alloy and compared it with the T6 aging. The microscopic results showed that the precipitates in the sample after T6 aging were mainly eta' and eta phases. The quenching and low-temperature secondary aging treatment in the T6I4 aging not only promoted the precipitation of the phases, resulting in high-density and fine precipitates inside the alloy. This provided a stronger dislocation bypassing effect, with the strength reaching 804 MPa (~ 28 MPa higher than that of the T6 sample). Furthermore, compared with the T6 sample, the T6I4 sample obtained more continuously distributed grain boundary precipitates (GBPs) and narrower precipitate free zones (PFZs) due to its higher nucleation rate, resulting in an improved elongation but reduced intergranular corrosion resistance.