Improvement of the Biodegradation Property and Biomineralization Ability of Magnesium–Hydroxyapatite Composites with Dicalcium Phosphate Dihydrate and Hydroxyapatite Coatings

The application of calcium phosphate reinforced magnesium matrix composites has not achieved the expected effect to control the degradation rate of magnesium so far. Therefore, in order to enhance the corrosion resistance and further develop the surface bioactivity of the composites to meet specific requirements of bone tissue engineering applications, biocompatible dicalcium phosphate dihydrate (DCPD) and hydroxyapatite (HA) coatings have been deposited on homemade HA/Mg composites using a simple conversion coating method and a subsequent alkali post-treatment, respectively. The conversion coating mechanism was studied by comparing coating processes on the composites, pure Mg, and an AZ60 Mg alloy. Electrochemical results showed that polarization resistance of the optimum DCPD and HA coatings was about 15 and 65 times higher than that of the composites, respectively. Immersion tests in simulated body fluid revealed that both coatings could supply improved corrosion resistance and biomineralization abilit...