Biocompatible DCPD Coating Formed on AZ91D Magnesium Alloy by Chemical Deposition and Its Corrosion Behaviors in SBF

Bioactive calcium phosphate coatings were prepared on AZ91D magnesium alloy in phosphating solution in order to improve the corrosion resistance of the magnesium alloy in Simulated Body Fluid (SBF). The surface morphologies and compositions of the calcium phosphate coatings deposited in the phosphating bath with different compositions were investigated by Scanning Electron Microscopy (SEM) with Energy Dispersive Spectrometer (EDS) and X-ray Diffraction (XRD). Results showed that the calcium phosphate coating was mainly composed of dicalcium phosphate dihydrate (CaHPO4
• 2H2O, DCPD), with Ca/P ratio of approximately 1:1. The corrosion resistance was evaluated by acid drop, electrochemical polarization, electrochemical impedance spectroscopy and immersion tests. The dense and uniform calcium phosphate coating obtained from the optimal phosphating bath can greatly decrease the corrosion rate and hydrogen evolution rate of AZ91D magnesium alloy in SBF.