Microstructure and Corrosion Resistance of Microarc Oxidation Coatings on AZ31 Magnesium Alloy Extrusion Profiles

Microarc oxidation coatings were prepared on the surface of AZ31 magnesium alloy profiles. Oxidation time of the coatings was between 5min-10min. The phase structure, surface morphology and corrosion resistance of the coatings were investigated using SEM, XRD, copper sulfate spot test and polarization curve test. The results indicate: the main phase compositions of the microarc oxidation coatings are MgO, Mg2SiO4 and MgSiO3; with increasing pulse voltage, the micropore diameter of the coating surface becomes larger, the micropore number reduces and the coating surface roughness increases; the corrosion current density of magnesium alloy reduces significantly after microarc oxidation treatment. The pulse voltage of microarc oxidation should be controlled between 240V-360V to obtain the best corrosion resistance.