Preparation And Corrosion Resistance Of Micro-arc Oxide Ceramic Film On The Surface Of Mg-Sn-Zn-Ca Magnesium Alloy

With the development of medical industry,magnesium alloy is gradually emerging in medical treatment.It has degradability,good biocompatibility and elastic modulus.And it can avoid"stress shielding effect"because it is close to the skeleton.But there are some shortcomings,among which corrosion resistance in the human body is a big problem.A new biological magnesium alloy Mg-Zn-Sn-Ca is explored in this paper.A micro-arc oxidation（MAO）ceramic film was prepared on the surface of the alloy by using micro-arc oxidation surface modification technology to improve the corrosion resistance of magnesium alloy after implantation.In this experiment,the content of potassium fluoride,sodium hydroxide and glycerol in silicate electrolyte system was optimized by orthogonal test to determine the optimal scheme.Ceramic films are prepared on the surface of matrix alloys by basic electrolyte in this paper.The effects of different treatment voltage and film forming time on the microstructure,surface porosity,roughness,thickness and corrosion resistance of the coating were explored.Treatment voltage is 350 V,400 V,450 V,500 V respectively.Film forming time is 3 min,4min,5 min,6 min respectively.The microstructure,phase composition,corrosion resistance and degradation properties of the MAO films by adding graphene oxide（GO）and nanometer TiO₂of different concentrations into the basic electrolyte were compared and explored.The results showed that the optimum solution for electrolyte was KF 8 g/L,Na OH 3 g/L,C₃H₈O₃10 m L/L,Na₂SiO₃10 g/Lthrough the film thickness,corrosion resistance and porosity.By controlling the variable method,the optimum treatment voltage and film forming time were explored.The results showed that the film layer had better corrosion resistance at 450 V treatment voltage,and thicker thickness,better compactness and better corrosion resistance at 5min.The results of XRD test and analysis show that the MAO films are mainly composed of MgSiO₃,Mg₂SiO₄and Mg O.It indicated that the main chemical reaction in the process of micro-arc oxidation is the process of melting oxidation on the substrate surface.When the GO is added to the base electrolyte,the thickness of the film will be reduced.The corrosion resistance of MAO film is best after 0.4 g/LGO is added to the electrolyte.When the GO content in the electrolyte is 0.5 g/L he corrosion resistance of the MAO film decreases.The surface roughness of the film after adding Nano-TiO₂into the base electrolyte was obviously improved.But it decreased when the concentration reached 8 g/L.When 8 g/LNano-TiO₂is added to the electrolyte,the corrosion resistance of MAO film is optimal,which provides a theoretical basis for the Mg-Sn-Zn-Ca biological magnesium alloy in the medical field.