Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro-arc oxidization technique

Abstract
With increasing applied voltage, three types of anodic coatings, passive film, micro‐spark ceramic coating and spark ceramic coating were made by micro‐arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali‐silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro‐spark ceramic coating, prepared in the voltage range of 170~220V exhibits compact, homogeneous structure and highest corrosion‐resistance.