Effects of Voltage on the Microstructure and Properties of Micro-Arc Oxidation Coatings of Zirconium Alloy

To enhance the wear and corrosion resistance of Zr alloy components in marine engineering, this study investigated the influence of the applied voltage (ranging from 470 to 620 V) on the morphology, structure, and properties of ceramic coatings formed on a Zr alloy substrate by Micro-arc Oxidation (MAO) in a silicate–phosphate composite electrolyte. The results showed that with increasing voltage, the coating thickness increased (from 15.12 to 52.80 μm) and the surface roughness increased (from 1.12 to 4.89 μm), while both the surface and cross-sectional porosity first increased and then reached their minimum values at 620 V (1.61% and 5.75%, respectively). Phase analyses indicated that the coatings consisted mainly of monoclinic ZrO2 (m-ZrO2), along with minor amounts of SiO2, ZrSiO4, and Zr3(PO4)4. The coating prepared at 620 V exhibited optimal performance: its hardness was 1.98 times that of the substrate, the wear volume decreased by approximately 87%, the self-corrosion potential shifted positively by 539 mV, the corrosion current density decreased by nearly two orders of magnitude, and the polarization resistance increased by approximately two orders of magnitude. These results demonstrate a substantial improvement in the service performance of Zr alloys for marine applications.