Electrochemical evaluation of constituent intermetallics in aluminum alloy 2024-T3 exposed to aqueous vanadate inhibitors

Experiments were conducted to determine how inhibiting forms of vanadate interact with complex Al alloy microconstituent intermetallics to impart corrosion protection. Cathodic polarization experiments on Al 2024-T3 indicate a strong correlation between inhibition and the presence of tetrahedrally coordinated vanadate. Anodic and cathodic polarization curves were measured on bulk synthesized Al2 Cu, Al2 CuMg, Al7 Cu2 Fe, and Al20 Cu2 Mn3 in alkaline 0.5 M NaCl solutions with and without 10 mM NaV O3. Vanadate additions generally decreased Ecorr, increased Epit, and decreased the cathodic kinetics of all tested materials. Because of decreased cathodic kinetics, open-circuit potentials (OCPs) were shifted in the active direction in aerated solutions when vanadate was present. This shift pins the OCP just below the observed pitting potential for Al2 CuMg in vanadate solution, effectively preventing breakdown and subsequent support of rapid oxygen reduction by Cu-enriched clusters. Ecorr, Epit, Erp, icorr, ipass, and i at -1.3 VSCE data from polarization experiments were summarized in cumulative distribution plots, and averages are presented in tabulated format. Scanning electron microscopy images of Al 2024-T3 used for 4 h of OCP measurement show that vanadate greatly decreased circumferential trenching around intermetallic particles in both aerated and deaerated solutions. Potentiostatic hold experiments were used to show suppression of Al2 CuMg dissolution in vanadate solutions.