Hydrothermal biomimetic modification of microarc oxidized magnesium alloy for enhanced corrosion resistance and deposition behaviors in SBF

Bioactive composite coatings with a microarc oxidation (MAO) bottom layer and a biomimetic top hydrothermal layer were developed on an AZ31B magnesium alloy by combined MAO and hydrothermal treatment. The composition and microstructure of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Potentiodynamic polarization and soaking test in simulated body fluid (SBF) were used to evaluate the biodegradation and bioactivity of coated magnesium. The results show that the bioactive top hydrothermal layer containing CaHPO₄, HA and Ca₃(PO₄)₂ grows on a 10μm thick MAO bottom layer. The corrosion current of samples with MAO-hydrothermal duplex layers is reduced to 4.780×10^-6Acm^-2, the corrosion potential is increased to -0.92V. The sealing pore effect of the top hydrothermal layer enabled the MAO bottom layer to obtain a significantly improved corrosion resistance property. The MAO-hydrothermal sample had a weight increase of 14.52mgcm^-2 compared to 24.7mgcm^-2 weight loss for the MAO bottom layer after 28days, due to the CaP compound deposition induced by the top hydrothermal surface.