Effect of zirconia sol on the microstructures and thermal-protective properties of PEO coating on a cast Al-12Si piston alloy

A triphase composite ceramic coating, Al2O3-ZrO2 together with a small amount of SiO2 was successfully grown on a cast Al-12Si system piston alloy by a novel plasma electrolytic oxidation process with different zirconia sol additions in sodium silicate electrolyte. It was found that the compactness of the coating increased significantly and the hindrance of Si element on plasma electrolytic oxidation process was weakened effectively, and then the growth rate of the coating was improved substantially with zirconia sol addition. Meanwhile, Zr element was gradient distribution in the inner layer. Both the content of c-ZrO2 and the heat-insulating property of the coating increased significantly. After 1000 cycles of thermal shock, there is no cracking in the coating surface, which indicates that the plasma electrolytic oxidation coating with zirconia sol additions possessed a good thermal shock resistance.