Influence of zirconia sol on microarc oxidation process of aluminum alloys

Aluminum alloy was processed by microarc oxidation method with a control mode of constant current density in phosphate electrolyte with in-situ and additional zirconia sol. The effects of zirconia sol on the microarc oxidation process were investigated. The variations of voltage and electrolyte parameters, the growth process and surface microstructure of coatings were analyzed. The results indicate that in the electrolyte with in-situ zirconia sol, pH values reduce less, conductivity increases less, arcing voltage and electrolyte temperature are lower, and the growth rate of coating is higher, which is about 2.9 μm/min. The ceramic layer obtained in electrolyte with in-situ zirconia sol is porous, the internal and external layers combine closely, the coating is thicker and the thickness is up to 85 μm. The ceramic layer prepared in the electrolyte with additional sol includes more volcano-like deposits and is loose. The ceramic layer is mainly composed of γ-Al₂O₃ and t-ZrO₂ phases.