Microstructure, Mechanical Properties, and Corrosion Resistance of ZrO2 Nanoparticle-Modified Micro-Arc Oxidation Composite Coatings

In this study, to further improve the performance of micro-arc oxidation (MAO) coatings, ZrO2 nanoparticles at different concentrations were added to the electrolyte. The effects of ZrO2 concentration on the microstructure, mechanical properties and corrosion resistance of the MAO composite coatings were systematically investigated. The coatings mainly consisted of α-Al2O3 and γ-Al2O3. The detection of ZrO2 confirmed the incorporation of the added particles. As the concentration increased from 0 to 6 g/L, the porosity decreased from 1.352% to 0.864%, whereas further addition increased the porosity. At 6 g/L, the mean microhardness reached 623 ± 50 HV0.05. Moreover, this coating showed the lowest friction coefficient of 0.135. In addition, its corrosion potential was −0.148 V, while its corrosion current density was 2.578 × 10−7 A·cm−2. It also exhibited the highest low-frequency impedance modulus. When the ZrO2 concentration was further increased, the coating porosity increased and the improvements gradually weakened. Overall, a suitable ZrO2 concentration promoted coating growth and reduced structural defects. It also improved the hardness, wear behavior and corrosion protection of the coating. Therefore, these findings provide a reference for the concentration design of ZrO2-modified MAO coatings. They also clarify the nonmonotonic relationship between coating growth, structural defects and performance.