| Magnesium and its alloy are characterized by its light weight, the simlilar Young’s modulus with human bone, its wonderful biocompatibility and biological activity, and magnesium ion plays an important part in the physiological environment of human body, it is an essential element in the human body. It’s been regarded as a potential bone substitute material.In order to slow down the rapidly corrosion rate of the magnesium alloy, surface treatment is an effective method for the protection of magnesium alloys. In this paper, we adopted chemical conversion method, electroless plating to prepare tin/zinc composite coating on AZ91 D magnesium alloy; moreover, we had a research on Ca-P/tin/zinc composite coating on the surface of AZ91 D magnesium alloy. These coatings that abovementioned are all for the sake of slowing down the rapidly rate of the hydrogen evolution and degradation to make it has a long term development in biomedical materials.At the beginning of the experiment, the tin and zinc coating was prepared on the surface of AZ91 D magnesium alloy by immersion plating method. Using a single variable way, the tin and zinc coating was prepared at different p H, temperature. We obtained a optimal process by observing the morphology of the film and the corrosion resistance in tafel. Furthermore, the tin/zinc composite film was prepared under the optimal process, we had a research on the influence of the number of the layer on the properties of the composite coating, the result shows that when the number of the layer was 11, the properties of the film is the optimum through SEM and electrochemical workstation. XRD and EDS analysis show that the main component of the coating are Zn(Sn O3), Zn2 Sn O4, Mg2 Sn O4, Mg F2, that the films have a protective effect on AZ91 D magnesium alloy.In additon, we prepared calcium phosphate coating on the surface of AZ91 D magnesium alloy at different p H, temperature. Finally we optain a optimum condition of p H=2.8, T=40℃ through the observation of the morphology and corrosion resistence of the coating. XRD and EDS analysis show that the main component of the film is DCPD. On account of the roughness and tinness of the calcium phosphate coating, the corrosion resistence is limited; hence, we had a research on the preparation of Ca-P/tin/zinc composite film on the surface of AZ91 D magnesium alloy. The SEM and eletrochemical workstation(include polarization curve and impedance spectroscopy) show that the comsite film improved the corrosion resistence effectively. The main component of the film are Mg F2, Ca HPO4.2H2 O, Ca10(PO4)6(OH)2, Zn2 Sn O4 through XRD and EDS analysis.At the end of the experiment, we soaked the four different conditions of the AZ91 D magnesium alloy(AZ91D, Ca-P coating, tin/zinc composite coating, ca-p/tin/zinc composite coating) in SBF solution for 7 to 15 days under the 37℃ constant temperature. From the polarization curve, impedance spectroscopy, p H, corrosion speed and the surface morphology, we know that all the films on the surface of AZ91 D magnesium alloy improved its corrosion resistence in a certain extent. But, the Ca-P/tin/zinc composite film has the best performance of corrosion resistence. |
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