Influence of alloyed Sc and Zr, and heat treatment on microstructures and stress corrosion cracking of Al-Zn-Mg-Cu alloys

Stress corrosion cracking (SCC) behavior of Al-Zn-Mg-Cu alloys with different Sc, Zr contents and heat treatments was studied using slow strain rate test. Grain boundary microstructures were identified by transmission electron microscopy (TEM) and statistical analysis. It was found that the SCC resistance of alloys is improved by increasing Sc, Zr contents and aging degree. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The results reveal that for Al-Zn-Mg-Cu-0.25Sc-0.10Zr (wt%) alloy with different aging degrees, hydrogen induced cracking dominates the SCC when the area fraction of GBPs is relatively low. For peak-aged Al-Zn-Mg-Cu alloy and Al-Zn-Mg-Cu-0.10Sc-0.10Zr (wt%) alloy, anodic dissolution dominates the SCC when the area fraction of GBPs is sufficiently high.