Inhibition of the localised corrosion of AA2024 in chloride solution by 2-mercaptobenzimidazole and octylphosphonic acid

The scanning vibrating electrode technique was employed to monitor the in situ localised electrochemical activity on aluminium alloy 2024-T3 at the free corrosion potential in aggressive NaCl solutions with and without corrosion inhibitors 2-mercaptobenzimidazole (MBI) and octylphosphonic acid (OPA). MBI is a very effective inhibitor against pitting corrosion, even in a chloride environment without the reservoir of MBI. In contrast, localised corrosion was observed at several points at the early stage of immersion of AA2024 in NaCl solution containing OPA. Ex situ energy-dispersive X-ray spectroscopy analysis of the Al2CuMg particle at the cross-section revealed that MBI does not entirely prevent its dissolution but reduces the dissolution rate and the rate of oxygen reduction by forming an insoluble complex compound Cu–MBI on the partially dealloyed AlCu-based particles, i.e., on the porous copper remnants. The MBI’s action is an efficient option for mitigating the corrosion of Cu-based aluminium alloys.