Formation mechanism of calcium phosphate coating on micro-arc oxidized magnesium

A calcium phosphate coating was prepared on the surface of micro-arc oxidized magnesium by a chemical method. The microstructure evolution of the coating was characterized by X-ray diffraction, Fourier-transformed infrared spectroscopy and scanning electron microscopy. The results showed that Ca10(PO4)6(OH)2 (HA) was firstly formed on the surface of micro-arc oxidized magnesium, followed by flake-like CaHPO4·2H2O (DCPD). The solution pH and Ca2+ concentration had intense influence on the formation of calcium phosphate coating. Acidic Ca2+ enrichment solution was favourable for HA formation on the surface of micro-arc oxidized magnesium. High concentration of HPO42− and low concentration of Ca2+ in acidic solution improved the formation of DCPD coating.

► Calcium phosphate coating on MAO magnesium was prepared by solution method.
► Acidic solution with high Ca2+ and low HPO42− improved HA coating formation.
► Acidic solution with high HPO42− and low Ca2+ improved DCPD deposition.
► Alkali condition favoured HA formation in solution, not on the substrate.