Corrosion Protective Film Formation on Mg Alloys AZ 31 by Exposure to Dilute Selenite Solutions.

The study of protective film formation on Mg alloys by exposure to sodium selenite solutions was conducted. Anodic polarization studies, electrochemical impedance spectroscopy studies, morphological analysis, and Energy-dispersive X-ray spectroscopy were performed on AZ31 Mg alloy after coating treatment in different concentrations of sodium selenite. The corrosion resistance was improved by around 5 times compared with control. Improved resistance to localized corrosion was observed in the coatings treated by 5 mM or 10 mM sodium selenite. The protection mechanism was ascribed to the transformation of selenite to insoluble selenium, the formation of insoluble MgSeO3 hydrate, and polymerization of amorphous selenium.