Structure and properties of composite aluminum oxide layers produced on magnesium alloys using hybrid method

Abstract Unlike aluminium oxide surface layers, magnesium oxide layers obtained by anodising processes exhibit some drawbacks, especially chemical instability in the presence of humidity, resulting in susceptibility to cracking and spalling. This work was dedicated to the development of a new hybrid method allowing us to produce composite aluminium oxide surface layers on magnesium alloys to ensure better performance properties than those achieved by magnesium oxide layers produced by commercial anodising. Composite aluminium oxide layers were produced on magnesium AZ91D alloy using a three stage hybrid method: magnetron sputtering deposition of an aluminium coating, followed by anodising in classical or plasma electrolytic oxidation (PEO) variant, combined with final tightening of the layer by hydrothermal treatment. The structure and the properties of the composite oxide layers were characterised. The investigations proved that the hybrid method using classical anodising is a promising method to improve the corrosion resistance of the AZ91D alloy much more efficiently than commercial anodising, but at the cost of decreased wear resistance. Based on preliminary investigation, a modified variant of the hybrid method using PEO treatment was found to result in both high wear and corrosion resistant composite aluminium oxide layers on AZ91D alloy, making it a prospective solution.