Preparation and Corrosion Resistance of Microarc Oxidation-Coated Biomedical Mg–Zn–Ca Alloy in the Silicon–Phosphorus-Mixed Electrolyte

Microarc oxidation (MAO) coating was prepared on the surface of the biomedical Mg–3Zn–0.2Ca alloy in a phosphate electrolyte with varying concentrations of Na2SiO3. The morphology, cross section, chemical composition, and corrosion resistance of the coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical polarization tests (EI), and in vitro immersion experiments. The addition of Na2SiO3 is performed to increase the thickness and compactness of the coating. When the Si/P atomic ratio is approximately equal to 1 (1.5 g/L Na2SiO3), the best corrosion resistance is achieved, while excessive addition may lead to coating defects such as voids and microcracks, resulting in decreased corrosion resistance. The competitive relationship between PO4 3– and SiO3 2– anions in the silicon–phosphorus microarc oxidation-mixed electrolyte is discussed. In this study, it was first proposed that, when Mg2SiO4 and Mg3 (PO4)2 phase contents were approximately the same, the synergistic improvement effect on coating corrosion resistance was the most effective.