Degradable behavior and bioactivity of micro-arc oxidized AZ91D Mg alloy with calcium phosphate/chitosan composite coating in m-SBF.

The degradation behavior of a MAO-AZ91D with a calcium phosphate/chitosan composite coating in the modified simulated human body fluid (m-SBF) was investigated by immersion experiments and electrochemical impedance spectroscopy. The compositions of the composite coating soaked in the m-SBF for different time intervals were studied by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, thermo-gravimetric analysis and differential thermal analysis. The microstructures of the composite coating at different soaking stages were observed by using a scanning electron microscope. Results show that the as-prepared composite coating could slow down the corrosion rate of the AZ91D alloy and it demonstrated good bioactivity in the m-SBF. The coating's morphology changed from a flake-like one into a spherical-shaped one with the increase of immersion time in the m-SBF.