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 Na 2 SiO 3 . 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 Na 2 SiO 3 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 Na 2 SiO 3 ), 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 PO 4 3- and SiO 3 2- anions in the silicon-phosphorus microarc oxidation-mixed electrolyte is discussed. In this study, it was first proposed that, when Mg 2 SiO 4 and Mg 3 (PO 4 ) 2 phase contents were approximately the same, the synergistic improvement effect on coating corrosion resistance was the most effective.