Formation of dicalcium phosphate dihydrate on magnesium alloy by micro-arc oxidation coupled with hydrothermal treatment

• Ca and P incorporated layers were prepared on Mg alloy by micro-arc oxidation (MAO).
• Ca and P inside the MAO layer existed with amorphous phase.
• Dicalcium phosphate dihydrate crystals were formed by hydrothermal treatment.
• MAO and hydrothermal treatment enhanced the biocorrosion resistance of Mg alloy.
• The pitting corrosion resistance of Mg alloy was improved greatly.

A layer containing dicalcium phosphate dihydrate (DCPD) and β-Ca3(PO4)2 was prepared on magnesium alloy by hydrothermal treatment of micro-arc oxide (MAO) layer. The biocorrosion resistance of the oxide layers before and after hydrothermal treatment was analyzed by anodic polarization and electrochemical impedance spectroscopy (EIS) in Hank’s solution. The prepared MAO layers consisted mainly of MgO and MgAl2O4, and Ca and P inside the oxide layers existed with amorphous phase. Hydrothermal treatments not only made the amorphous Ca and P change into DCPD and β-Ca3(PO4)2 crystals, but also improved the biocorrosion resistance of magnesium alloys, especially the pitting corrosion resistance.