Micro-structure and Composition of Ceramic Coating on AZ91D Magnesium Alloy Prepared by Micro-Arc Oxidation

A crossion-resistance ceramic coating was prepared on AZ91D magnesium alloy by micro-arc oxidation method with an asymmetric ac power supply. Silicate-based and aluminate-based electrolyte were adopted in the micro-arc oxidation process, and it shows that the coating formed in silicate solution is more continuous and compact than that formed in aluminates solution, In order to understand the effect of processing parameters upon the micro characteristics of the formed ceramic coating, many micro-analytical methods of SEM, EDS and XRD were used to study the morphology and microstructure of the ceramic coating. It was found that the coating consists of two layers, i.e., loose layer and compact layer, and the elevated current density will lead to the increment of micropore size in loose layer. The compositions and phase structures varied with the electrolyte components, and it was also known that the micro-arc oxidation coating prepared in silicate solution is composed of MgO and Mg2SiO4, while the coating prepared in aluminate is mainly composed of MgAl2O4.