Evaluation of the long-term anticorrosion behavior of (OCP + Ca-P)/MAO coated magnesium in simulated body fluids

Abstract

Magnesium has attracted wide interest as a biodegradable metal implant. However, the weak corrosion resistance restricts its practical applications. A CaP sealing coating was prepared on the surface of microarc-oxidation coating (MAO)-coated Mg via a liquid-phase deposition. The liquid-phase deposition time affects not only the microstructure and phase composition of CaP coating, but also the long-term anti-corrosion and biodegradability of the MAO coated Mg. The phase composition of the CaP coating evolves from octacalcium phosphate (OCP) + Ca-P compound (Mg-containing) to Ca2.86Mg0.14(PO4)2 with increasing deposition temperature. Mg with (OCP + Ca-P compound)/MAO coating exhibits outstanding anti-corrosion property during 60 days of immersion in simulated body fluids. Meanwhile, the OCP + Ca-P compound coating can facilitate the deposition of osteoconductive minerals, i.e., the hydroxyapatite layer, on the OCP coating during immersion in SBF solution. A rational model for the anticorrosion procedure of the Mg with (OCP + Ca-P)/MAO coating in SBF solution for a long-time immersion is proposed.