Preparation Al2O3/ZrO2 composite coating in an alkaline phosphate electrolyte containing K2ZrF6 on aluminum alloy by microarc oxidation

Al2O3/ZrO2 composite coating was prepared on 2A70 aluminum alloy by microarc oxidation (MAO) in a phosphate electrolyte containing K2ZrF6. The effects of K2ZrF6 in the electrolyte on the coating thickness, surface morphology, elemental composition and abrasive resistance were investigated. The results indicated that the MAO coating thickness increase due to the addition of K2ZrF6 in the electrolyte. In the electrolyte containing 6.0 g/L K2ZrF6, the coating was the most uniform and compact. The MAO coating formed in the electrolyte without K2ZrF6 was mainly composed of γ-Al2O3 and a little α-Al2O3. Zirconium in the form of t-ZrO2 was detected in the MAO coatings formed in the electrolyte containing K2ZrF6, and the Zr content increases with increasing concentration of K2ZrF6. A γ-Al2O3 and t-ZrO2 nanocomposite coating was formed in the electrolyte containing 6.0 g/L K2ZrF6, and which exhibited the highest abrasive resistance.