Intermetallic Phases in Aluminum Alloys and Their Roles in Localized Corrosion

The intermetallic phases in AA7075-T6, including the nm-scale precipitate MgZnCu and 10-μm size Mg2Si, S-phase, Al7Fe2Cu(Mn), and Al15(FeMn)3(SiCu)2, were identified and evaluated with respect to chemical composition, structure, and relative nobility. Evaluation of each major intermetallic particle (IMP) after exposure of the alloy to electrolyte allowed assessment of their roles in the localized corrosion. Different corrosion scenarios, including dealloying, trenching, particle etching out/dissolution, localized anodic and cathodic behavior of the IMPs, and corrosion sequences were studied. Combined with previous studies, the results advance the understanding of the electrochemical properties and the associated mechanisms of localized corrosion in aluminum alloys.