Effects of Electrical Parameters on Microarc Oxidation of AZ91D Magnesium Alloy

Ceramic coatings on AZ91D magnesium alloy were prepared by microarc oxidation with different electrical parameters in a silicate-aluminate dual electrolyte solution. Surface morphology and film thickness of the coating were characterized by scanning electron microscopy (SEM) and layer thickness meter. The results showed that the non-uniformity of the coating increased gradually with increasing the current density, duty cycle and oxidation time. The diameter of the discharge aperture increased but the number of discharge apertures decreased with increasing the current density, duty cycle and oxidation time. Extinguish arc stage appeared during the process of micro-arc oxidation when the current density was more than 10 A/dm2 or the oxidation time was more than 15 minutes. With the increase of current density, the thickness of the coating increased linearly first and then kept in a constant. Similarly, the thickness of the coating increased gradually with the increase of the duty cycle and oxidation time.