The Preparation And Characterization Of Fluoridated Ca-Mg-P Composite Coating On Magnesium Alloy

The exploitation of biodegradable bone repair materials has been the appealing research in the field of biomaterials.In which,magnesium and its alloys had desirable mechanical property,biocompatibility and biodegradability.However,the rapid degradation of magnesium alloys implants limits their clinical applications.Therefore,it was expected to control the corrosion rate of magnesium alloy in body fluids and improve the long-term corrosion resistance of magnesium alloys to maintain sufficient long-term mechanical properties and bioactivity so as to realize the clinical application of biomedical magnesium alloys.The surface modification of magnesium alloys was considered as one of the important ways to improve the corrosion resistance for magnesium alloys.In this work,a fluoridated Ca-Mg-P composite coating was prepared on AZ31magnesium alloy substrate via hydrothermally assisted sol-gel method.And through regulating the fluoridated content and preparation process of coating such as pH value of sol,hydrothermal temperature and hydrothermal time,the composition and structure of coating could be effectively controlled so that the electrochemical behaviors and long-term corrosion resistance of composite coatings could be adjusted.When F^-concentration of coating sol in range from 0.01 M to 0.04 M,composite coatings were composed of Mg（OH）₂,FHA and NH₄MgPO₄·H₂O.With fluoridated content of coating sol increasing,phase contents of composite coatings changed,the surfaces became denser gradually and looser later,the thickness increased gradually and decreased later.When F^-concentration of coating sol was 0.03 M,pH value of the sol was 10,hydrothermal temperature was 140℃and hydrothermal time was 6 h,a dense and coarse composite coating could be prepared on the surface of magnesium alloy.In simulated body fluid,the AC impedance of the composite coated magnesium alloy sample was 293 kΩ·cm²,significantly improving the corrosion resistance of magnesium alloy.In the process of immersing in simulated body fluid,the coating could rapidly induce the formation of hydroxyapatite,thickness of coatings and mineralized layers increased gradually.On the 49^thh day,the whole thickness of coating and mineralized layer reached 60μm and the corrosion rate was 5.60×10^-3mm/d.During the immersion of 98 days,pH value of stimulated body fluid fluctuated slightly under 8.It indicated fluoridated Ca-Mg-P composite coating could provide the long-term protection for magnesium alloy and improve the bioactivity of magnesium alloy.