Structure and Properties of Hydroxyapatite-Containing Ceramic Coatings on AZ31 Mg Alloy Treated with Different Applied Frequencies

Abstract—Mg and its alloys have attracted much interest as biodegradable metallic biomaterials applied in orthopedic implants. However, rapid degradation of Mg alloys in biological tissues has prevented their clinical application. In this study, Ca-deficient hydroxyapatite (Ca-def HA) coatings were directly prepared on the surface of AZ31 Mg alloy by micro-arc oxidation (MAO) to improve its biocompatibility and corrosion resistance. Effects of applied frequency on the microstructure, phase composition, bonding strength, and corrosion resistance of coating samples were studied by scanning electron microscopy (SEM), X-ray diffractometer (XRD), energy-dispersive X-ray spectroscopy (EDS), and potentiodynamic polarization tests. The corrosion resistance of Mg alloy could be significantly improved by MAO treatment. Application of a higher frequency decreased the pore size of discharge channels and led to a thinner, compact coating layer. The coating formed at 2000 Hz demonstrated the highest polarization corrosion resistance in this study.