Electrochemical Evaluation of Constituent Intermetallics in Aluminum Alloy 2024-T3 Exposed to Aqueous Vanadate Inhibitors

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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 Al_2Cu, Al_2CuMg, Al_7Cu_2Fe, and Al_20Cu_2Mn_3 in alkaline 0.5 M NaCl solutions with and without 10 mM NaVO_3. Vanadate additions generally decreased E_corr, increased E_pit, 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 Al_2CuMg in vanadate solution, effectively preventing breakdown and subsequent support of rapid oxygen reduction by Cu-enriched clusters. E_corr, E_pit, E_rp, i_corr, i_pass, and i at −1.3 V_SCE 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 Al_2CuMg dissolution in vanadate solutions.




K. D. Ralston, T. L. Young and R. G. Buchheit, "Electrochemical Evaluation of Constituent Intermetallics in Aluminum Alloy 2024-T3 Exposed to Aqueous Vanadate Inhibitors," Journal of the Electrochemical Society 156, no. 4 (2009), doi:10.1149/1.3076147