Enhancement of Localized Corrosion in Aluminum Alloys by Weak Acids

Al-1Cu solid solution and a 2024-T3 (UNS A92024) industrial alloy were tested for localized corrosion resistance in sulfate and chloride solutions, with and without a dilute boric acid (H3BO3)/borate addition (0.01 M H3BO3 adjusted to pH 7). The susceptibility to pitting and crevice corrosion was enhanced by the low concentration of weak acid in the buffer, which prevents alkalization at cathodic sites and the consequent consumption of cathodic current by alkaline dissolution of the adjacent alloy matrix. In the presence of a weak acid, there is more cathodic current available to drive remote pits and crevice corrosion sites. A range of techniques including coupled electrodes and electrochemical noise was used.