Preparation And Characterization Of Micro-arc Oxidation Layer On Magnesium Alloy For Biomedical Applications

As a biodegradable material,magnesium alloy has a bright futurefor application.But the use of Mghas been restricted because of poor corrosion resistance.This dissertation made protective oxide layer on magnesium alloy by micro arc oxidationtreatment in order to improve the corrosion resistance,and make sure thatthe magnesium alloy has a good biocompatibility.Micro arc oxidation(MAO)layers were prepared with different(NaPO3)6 concentrations and different voltages,respectively.The thickness,roughness,phase constitution,surface and cross section morphology were characterized by coating thickness gauge,roughness tester,X-ray diffraction(XRD),scanning electron microscopy(SEM),respectively.The corrosion resistance of the MAO layers was characterized by drop test,electrochemical experiment and full immersion test.The biocompatibility of the MAO layers wasevaluated by hemolysis experiment and osteoblasts culture in vitro.The results showed that with the increase of the(NaPO3)6,the thickness and roughness of MAO layers increased,and the micro pores became larger.The layers were consist of MgO,Mg2SiO4,Mg3(PO4)2.When the concentration came to a higher level,micro cracks appeared obviously.The corrosion resistance of magnesium alloy was significantly improved after micro arc oxidation treatment.The corrosion resistance increased and then deteriorated with the increasing concentration.The optimal corrosion resistance appeared when the(NaPO3)6 was 5 g/L.When the voltage increased,the thickness and roughness of the layers increased,and the micro pores became bigger.It was found that some micro cracks came out when the voltage was too high.With the voltage increased,the corrosion resistance of the layers roseat first and then dropped down.The MAO layer prepared under 400V obtained the best corrosion resistance.The pH of all samples after long term immersion ascended at first,and then decreased gradually.At last the pH value maintained at a relatively stable level with time went on because of the formation of corrosion products.Magnesium alloy showed an obvious hemolysis effect.But the hemolytic rates of the MAO layers were between 1%and 3%.The hemolysis effect was eliminated.The MAO layer with the best corrosion resistancewas chosen to perform the cell culture in vitro by indirect contact method.It was found that the MAO layer had no adverse effect on proliferation or cell morphology.Good biocompatibility was obtained by magnesium alloy after micro arc oxidation treatment.