The Composition and Hardness of the Coating Containing Zirconia Produced by Micro-Arc Oxidation on Aluminium Alloy

In this paper, a ceramic coating containing zirconia was produced by micro-arc oxidation (MAO) in a solution of K2ZrF6 and KOH. The composition and structure of the coating were investigated by XRD, EPMA. The results show that the coating consists of t-ZrO2, m-ZrO2, alpha-Al2O3 and gamma-Al2O3. t-ZrO2 and m-ZrO2 distribute in outer layer of the coating, however, alpha-Al2O3 appears in inner layer of the coating. The coating surface consists of many micro-powders with a size of 1-2 mu m. It is because K2ZrF6 is unstable in the alkaline solution, and it can form zirconium hydroxide and takes part in the formation of the coating. The result of the hardness shows that the maximum hardness (1900HV) appears at around 30-50 mu m from the interface of substrate/coating.