Inhibition of Aluminum Alloy 2024 Corrosion by Vanadates: An In Situ Atomic Force Microscopy Scratching Investigation

The morphology and kinetics of the localized corrosion of aluminum alloy (AA)2024-T3 (UNS A92024) at the open-circuit potential were investigated by in situ atomic force microscopy (AFM) scratching. The addition of metavanadate to chloride solutions resulted in outstanding corrosion inhibition. Samples exposed to 0.1 M sodium chloride (NaCl) with no inhibitor developed a trench-like attack at the periphery of large Al-Cu-Fe-Mn-(Si) intermetallic phases. The addition of dilute metavanadate markedly reduced the kinetics of the attack. In addition, most S-phase particles remained free of attack. Higher concentrations of metavanadate increased protection even further so that only high AFM tip forces could induce pitting corrosion. Corrosion attack was immediately observed when AA2024-T3 samples were exposed to chloride solutions containing orange decavanadates. The attack nucleated on the exposed surface but not under the AFM tip. The attack grew continuously, accompanied by gas evolution and formation of corrosion products. Optical inspection after the test indicated severe corrosion damage, confirming an overall poor performance of orange decavanadate solutions as corrosion inhibitors.