The effects of coating time on the properties of nanostructured alumina-zirconia coatings applied on 7075 Al Alloy by plasma electrolytic oxidation (PEO)

To improve mechanical properties of the 7075 Al alloy, alumina-zirconia nanostructured coatings were formed on it through Plasma Electrolytic Oxidation (PEO) operated in potentiostatic mode. The composite coatings were produced at 450V for 100-300s growth times in a stable electrolyte containing K2ZrF6. Phase evaluation of the layers coated at 200s and higher growth times proved alumina-zirconia layers comprising tetragonal zirconia (t-ZrO2) and  and -Al2O3 phases. Nanostructured alumina-zirconia coatings with 20-40 nm particles size, porous structure and increase in the porosity content by increasing growth times proved by microstructural investigation of the layers. The coating thickness was in the range of 12-19 m. The distribution of Al, Zr and O elements in the cross-section of the coatings was uniform. Significant enhancement in hardness for coated samples was achieved (about 10 times higher than bare samples).