Effect of voltage on the morphology and corrosion resistance of microarc oxidation ceramic coatings on Mg–Gd–Y–Zn–Zr rare-earth magnesium alloy

Ceramic oxide coatings were fabricated on Mg–9Gd–3.5Y–2Zn–0.4Zr rare-earth magnesium alloy by microarc oxidation. The effects of the applied voltage (250, 300, 350, and 400 V) on the surface morphology, microstructure, phase composition, surface roughness, coating thickness, and corrosion resistance were systematically investigated. As the voltage increased from 250 to 400 V, the porosity first decreased from 6.29% to 3.73% and then increased to 4.51%. The average pore size increased from 287.95 to 644.09 nm, the coating thickness increased from 3.93 to 7.13 μm, and the surface roughness increased from 0.31 to 0.67 μm. The coating formed at 300 V exhibited a dense microstructure with an average pore size of 367.34 nm, a coating thickness of 6.42 μm, a relatively low surface roughness of 0.38 μm, and a high adhesion strength of 6.65 N. In addition, it showed superior corrosion resistance in both immersion and salt spray corrosion tests. The results indicate that the applied voltage plays a critical role in determining the structure and performance of the coatings, providing a reference for the surface treatment of magnesium alloys for engineering applications.