Preparation And Characterization Of Fluoride-incorporated Plasma Electrolytic Oxidation Coatings On The AZ31 Magnesium Alloy

In recent years,due to the excellent mechanical properties and degradability,magnesium alloys have attracted extensive attention of researchers and become a major choice of medical implant materials.However,the corrosion potential of magnesium alloys is relatively low and easy to be corroded,especially in body fluids containing chloride ions,whose uncontrollable degradation rate cannot meet the requirements of implant materials,which limits the application and development of magnesium alloys in the biological field.Therefore,surface modification of magnesium alloys to improve their corrosion resistance and biological activity has become a hot research.Objective:to study the corrosion resistance and biocompatibility of AZ31magnesium alloy with different fluorine content by preparing different fluorine content micro-arc oxidation film on the surface.Methods:This experiment was divided into five groups（AZ3,C-0,C-5,C-10,C-15）,and phosphate electrolyte was used to prepare micro-arc oxidation coatings with different fluorine contents by adding different amounts of KF.The morphology,phase,and chemical elements of the coating were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,and energy-dispersive X-ray spectrometry（EDS）.The change in the corrosion resistance with different fluorine contents was investigated by electrochemical experiments,hydrogen evolution,and long-term immersion tests.In addition,the cytotoxicity of each group was detected by CCK-8 and cell morphological observation.Results:Micro-arc oxidation films with different fluorine contents were successfully prepared on the surface of AZ31 magnesium alloy.With the increasing KF content in electrolyte,the fluorine content increased by EDS,while the number of micropores decreased and the pore diameter increased in SEM.The result of XRD shows that the peak of MgF₂ is gradually significant.Of course,the cross-sectional structures show that the thickness of the film layer increases gradually.The corrosion resistance research shows that with increasing content of KF,the potentiodynamic polarization curves show that the corrosion potential(E_corr)increases and corrosion current density(I_corr)decreases gradually.In addition,the impedance spectroscopy,hydrogen evolution and long-term immersion test also indicated that the corrosion resistance gradually enhanced with the increase of KF content.CCK-8 tests showed that cell proliferation accelerated with the increase of KF content.However,cell growth was inhibited when fluoride content exceeded a certain value（C-10）.Conclusion:With the increasing KF content,the corrosion resistance was gradually improved,and the cytocompatibility test showed a tendency of first increasing and then decreasing.