Microarc oxidation of corrosion resistant ceramic coating on a magnesium alloy

A ceramic coating was fabricated on AZ31B magnesium alloy in alkaline silicate solution by microarc oxidation to improve its corrosion resistance. XRD analysis indicates that the ceramic coating is composed of spinel phase Mg2SiO4 and MgO. SEM images indicate that the coating is composed of two layers, a porous outer layer and a dense inner layer. A few circular pores of 1–3 μm diameter are present in the porous outer layer, but they do not penetrate the dense inner layer. The corrosion resistance of magnesium alloys coated with ceramic coating was improved considerably as verified by potentiodynamic polarization curves and weight loss measurement in 3.5 wt.% NaCl solution.