Preparation and properties of composite MAO/ECD coatings on magnesium alloy.

Magnesium alloys are potential biodegradable implants because of their outstanding biological performance and biodegradability in the bioenvironment. However, the rapid corrosion of magnesium and its alloys in human body fluids or blood plasma limits their clinical application. In the present work, we first fabricated porous micro-arc oxidation (MAO) coatings containing Ca/P on the magnesium alloy substrate by conducting MAO in the electrolyte containing calcium gluconate. Subsequently, hydroxyapatite (HA) coatings were prepared using electrochemical deposition (ECD) on the MAO coatings. Finally, a MAO/ECD composite coating was successfully fabricated on the magnesium alloy. The phase, morphology and composition of the biological coatings were monitored with X-ray diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy, and corrosion resistance was evaluated by means of electrochemical methods in a simulated body fluid. The experimental results indicated that the formation of HA-containing composite coatings on magnesium alloy effectively decreases its corrosion rate and more importantly endows it with a potential bioactivity. We believe that the combined use of MAO and ECD to modify magnesium alloys would make them more attractive for clinical applications.