Corrosion inhibition of aluminium alloy AA6063-T5 by vanadates: Local surface chemical events elucidated by confocal Raman micro-spectroscopy

Chemical interactions between aqueous vanadium species and aluminium alloy AA6063-T5 were investigated in vanadate-containing NaCl solutions. Confocal Raman and X-ray photoelectron spectroscopy experiments were utilised to gain insight into the mechanism of corrosion inhibition by vanadates. A greenish-grey coloured surface layer, consisting of V⁺⁴ and V⁺⁵ polymerized species, was seen to form on the alloy surface, especially on top of cathodic micrometre-sized IMPs, whereby suppressing oxygen reduction kinetics. The results suggest a two-step mechanism of corrosion inhibition in which V⁺⁵ species are first reduced to V⁺⁴ or V⁺³ species above cathodic IMPs, and then oxidized to mixed-valence V⁺⁵/V⁺⁴ polymerized compounds.