Effect of zirconia sol in electrolyte on the characteristics of microarc oxidation coating on AZ91D magnesium

The microarc oxidation coatings were prepared on AZ91D magnesium alloy in a Na ₂SiO ₃-KOH electrolyte with and without zirconia sol, respectively. The effect of zirconia sol as an additive in the electrolyte on the surface morphologies, compositions, structures, and corrosion resistances of the coatings were investigated. It was found that the coating formed in the Na ₂SiO ₃-KOH electrolyte with zirconia sol has more uniform morphology, less micropores and cracks than that formed in an electrolyte without zirconia sol. The phase compositions of the coatings also varied after addition of zirconia sol in the electrolyte, owing to the participation of zirconia sol in the reaction and its incorporation into the oxide coating, and Zr existed in the form of Mg ₂Zr ₅O ₁₂. The results of potentiodynamic polarization analysis show that the coating formed in the electrolyte with zirconia sol increases significantly corrosion resistance for magnesium alloy.