Wear and corrosion characteristics of novel alumina coatings produced by micro arc oxidation on AZ91D magnesium alloy

Magnesium alloys are attractive materials for reducing the weight of the engineering components. Despite their high strength to weight ratio, poor corrosion and wear performances limit their extensive usage. In this respect, improvement of their wear and corrosion resistance by coating processes is a necessity for magnesium alloys. In this study, the wear and corrosion performances of AZ91D magnesium alloy have been examined after magnesia and alumina coatings. While micro arc oxidation (MAO) process was applied to generate a magnesia layer, cold spraying (CS) and MAO processes were combined to obtain novel alumina layer. CS was conducted to cover the substrate by depositing an aluminum layer (monolithic or composite). Afterwards, application of the MAO process produced an alumina layer on the deposited aluminum layer (monolithic or composite) forming a multi-layered coating on the examined magnesium alloy. Results of the experiments revealed that the alumina layer formed on the alumina reinforced aluminum matrix composite layer ensured superior protection for AZ91D alloy against mechanical and chemical degradations as compared to the magnesia layer.