Dislocation-aided electrochemical behavior of precipitates in stress corrosion cracking of Al–Zn–Mg–Cu alloys

The effects of electrochemical behavior of precipitates and dislocations on the stress corrosion cracking (SCC) of Al–Zn–Mg–Cu alloys were investigated. Fine anodic η (MgZn2) precipitates were readily dissolved, providing continuous channels for intergranular cracking, and coarse cathodic Cu-rich precipitates led to localized pitting attack of the surrounding matrix. This indicates that both precipitates promote intergranular SCC failure. Additionally, SCC resistance was decreased by stress localization owing to the high dislocation density on coarse Cu-rich particles. Our results demonstrate that tailoring the alloying content combined with T6 heat treatment is beneficial for increasing SCC resistance to compensate for the harmful effect of precipitates on SCC.