Effect of TiO2 nanoparticles on the corrosion resistance, wear, and antibacterial properties of microarc oxidation coatings applied on AZ31 magnesium alloy

Abstract

Microarc oxidation (MAO) is a surface modification process that is often adopted to produce a hard oxide layer on magnesium alloys to improve their corrosion resistance and wear resistance. However, under continual corrosion, the characteristic porous microstructure of MAO coatings provides diffusion paths that allow corrosive species to penetrate the coatings and react with the substrate underneath. Therefore, the present study investigated the modification of the microstructure of MAO coatings when adding TiO2 nanoparticles to a fluoride-containing silicate electrolyte system under the bipolar current mode. The results indicate that as the concentration of TiO2 nanoparticles increased, the quantity of rutile (TiO2) incorporated in the MAO coating increased, which led to the coating exhibiting an elevated hardness and a color change from white to gray-black. When the TiO2 concentration in the electrolyte was increased from 2.5 to 7.5 g/L, the total impedance of the MAO coating in electrochemical impedance spectroscopy analysis increased from 107 to >600 kΩcm2, which indicates that the corrosion resistance of the coating increased with the number of defects on it decreased. The addition of TiO2 enhances the photocatalytic properties of MAO coatings. However, excessive addition of TiO2 can lead to an adverse effect on the wear resistance of MAO coatings.