Characterization and biodegradation behavior of micro-arc oxidation coatings formed on Mg-Zn-Ca alloys in two different electrolytes

MAO coatings were obtained on self-designed Mg alloy by micro-arc oxidation process in calcium phosphate and silicate based electrolytes. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used to analyze the microstructure, cross sectional morphology, elemental distribution and composition of the MAO coatings. The corrosion resistance of the MAO coatings was evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in SBF solution. It was found that the electrolyte composition has a significant effect on the resulting coating characteristics, such as microstructure, composition, coating thickness, thus on the corrosion behavior. The corrosion resistance of the MAO coating formed in silicate electrolyte is superior at the initial immersion time while the CaP-containing coating demonstrates better corrosion behavior at the long-term time.