Study On Biomimetic Passivation/Cathodic Electrodeposition Of Mg Alloy

As a kind of hard tissue implant material, magnesium alloy has a lot of propertiessuperior to other biomedical metal materials, but its poor corrosion resistance performancelimits the application in biomedical fields. The apatite has both good chemical stability andbiocompatibility, but pure apatite has poor ability for bearing applications due to its lowstrength and brittle. So preparing bioactive calcium phosphate composite coating onmagnesium alloy surface will gather the strength and the toughness of the magnesium alloyand corrosion resistance and biological compatibility of apatite, which satisfy the requirementof human hard tissue repair replacement materials in the clinical application.This paper selects AZ91D magnesium alloy as mian research object, use the method ofbionic passivation to prepare calcium phosphate coating firstly, and use a kind of fastevaluation technique for mateirials——Achromic method to optimize the formula ofpassivation solution. After using scanning electron microscopy（SEM） to analyze themicrostructure of bionic passivation membrane which is prepared with the best formula, it isfound that the morphology of coating prepared by bionic passivation is needle flake shape;The result of X-ray diffraction（XRD） analysis shows that, the main composition of the bionicpassivation coating is DCPD（CaHPO₄·2H₂O）. The modern electrochemical test technology isused to investigate the mechanism of bionic passivation behavior on magnesium alloy, it isfound that the speed is stable during the coating process when adding calcium nitrate topassivation liquid, and when adding calcium chloride to passivation liquid, the speed of thecoating proces is fast in the beginning, then slow down, and achieve a dynamic balance verysoon in the end.Then, use bionic passivation as pre-treatment technology, use cathodic depositionmethod as “sealing hole” and “reinforce” technology, the preparation of bionicpassivation-cathode deposition combined treatment on the surface of AZ91D is realized. Theresult of achromatization experiment show that, the bionic passivation pre-treatment canimprove the effect of cathode deposition modification notably. Compared with the directcathode deposition treatment, combined treatment can make corrosion resistance of the filmincreased by114.95%. The analysis result of SEM and XRD show that, the coating preparedby combined technology is more uniform and dense, the cathode deposition coating isslate-shape grains; The main composition of coating which prepared from cathode depositionin NH4H2PO4/Ca（NO3）2·4H₂O combined system is DCPD; The coating prepared fromcathode deposition in KH2PO4/CaCl2combined system is mostly comprised of DCPD with small amount of HA.