Study Progress of ZrO2-Containing Micro-Arc Oxidation Composite Coatings on Surface of Magnesium Alloys

Poor corrosion resistance of magnesium alloys dramatically limits their application in corrosive environments.Microarc oxidation(MAO) technology can prepare a ceramic-like coating on the surface of magnesium alloy，which is an effective method to improve its corrosion resistance.Due to the film formation mechanism of MAO technology，there are many pores and cracks in the coating，and usually the coating is mainly composed of MgO，which would absorb water or deliquesce in wet and acidic environments，making the coating present bad corrosion resistance.Incorporating ZrO2 with excellent chemical stability and high hardness into magnesium alloy MAO coating to obtain a coating mainly composed of ZrO2 or a ZrO2-containing coating can improve the protection effect on the substrate.This paper reviewed the research progresses of the preparation technology，film formation mechanism and corrosion resistance of ZrO2-containing MAO composite coatings on magnesium alloys from the aspects of electrolyte，electric parameter，two-step MAO process，and combining MAO with other surface treatment techniques.In addition，the problems and shortcomings of each research direction were analyzed.In the future，it is necessary to optimize the electrolyte composition to ensure its stability and effectiveness and clarify the consumption and replenishment rules of each electrolyte component during the usage.The two-step MAO process should be further studied to obtain a composite MAO coating with better protection effect on the magnesium alloy matrix.Combination of MAO and other surface treatment techniques should be explored to utilize the advantages of two technologies and coatings comprehensively.The temperature field distribution and MAO coating forming mechanism can be further analyzed based on the structure transformation of ZrO2 at different temperatures.