Surface and corrosion properties of AA6063-T5 aluminum alloy in molybdate-containing sodium chloride solutions

Corrosion properties of aluminum alloy AA6063-T5 were investigated in molybdate-containing NaCl solutions. Electrochemical, microscopic, and spectroscopic experiments were utilized to examine the mechanism of corrosion inhibition by molybdates. SEM-EDX, magnetic force, and intermodulation electrostatic force microscopy data suggested that the inhibition initiation preferentially occurred over Fe-rich cathodic IMPs. Spectroscopic measurements demonstrated that the formed surface layer consists of mixed Mo(VI, V, IV) species. This layer provided inhibition with an efficiency of ∼90% after 4 h of exposure. High efficacy of ∼70% was achieved even after one week of exposure. A two-step oxidation-reduction mechanism of corrosion inhibition by aqueous molybdates was proposed.