Long term durability studies on the corrosion inhibition effect of 2-mercaptobenzimidazole (C3H4N2S) on AA6022: Mechanism of film formation and influence of IMPs

This study explores stability and variations of a mercaptobenzimidozole-inhibitor-based film upon the surface of Al alloy AA6022 and its contribution to the long-term corrosion inhibition in 0.1 M NaCl. Results provide a deeper insight and understanding of the mechanisms of combined inhibitor film formation and oxide layer growth, up to 240 h exposure, and the effect that the intermetallic particles have on the resultant film stability within these regions. Electrochemical impendence spectroscopy (EIS), potentiodynamic polarization (PDS) and X-ray photoelectron spectroscopy (XPS) studies reveal the formation of a porous, defective oxide layer on the alloy surface under uninhibited conditions. The addition of inhibitors results in the creation of a cathodically controlled system and the formation of a thin inhibitor-oxide mixed film, through the chemical absorption of inhibitor molecules to the substrate via S atom in association with O, thus reducing the corrosion rates. Focus ion beam scanning electron microscopy further confirms the presence of a combined oxide layer and inhibitor film, which covered both the alloy matrix and intermetallic regions. In addition, activity reduction of the Fe rich IMPs is thought to have occurred.