Correlation between stress corrosion cracking resistance and grain-boundary precipitates of a new generation high Zn-containing 7056 aluminum alloy by non-isothermal aging and re-aging heat treatment

The new generation high Zn-containing 7xxx series aluminum alloys were more prone to stress corrosion cracking (SCC) compared with the traditional 7xxx series aluminum alloys. However, the effect of grain boundary precipitates (GBPs) characteristics, especially microchemistry, on SCC of new generation high Zn-containing 7xxx series aluminum alloys were not investigated in sufficient detail. In the paper, the GBPs characteristics of a new generation high Zn-containing 7056 aluminum alloy were prepared by different aging heat treatments. The morphology and microchemistry of GBPs were analyzed by transmission electron microscope equipped with super-X energy disperse spectroscopy. The stress intensity factor (KI) and SCC propagation velocity(v) were measured by double cantilever beam (DCB) experiment. The correlations between the GBPs microchemistry and SCC resistance had been discussed. The results showed that the SCC resistance of a new generation high Zn-containing 7056 aluminum alloy was significantly improved by high termination temperature non-isothermal aging and re-aging heat treatment compared with T6 and T77 aging heat treatment. In addition, it was indicated that the SCC resistance was positively with the Cu content of GBPs.