| With the development of modern science and technology, the metal materials used in medicine have been paid more and more attention. The magnesium alloy has a well application prospects in bio-medical field, due to the advantages, such as good biocompatibility and low stress shielding effect. However, magnesium alloy is the positive material, its electrochemical activity is between Ca and Al, the potential is about-2.37 V. It is prone to occurring various corrosion, especially in the human body fluid environment. Therefore, it is very important to improve the corrosion resistance of magnesium alloy in the biological environment.To solve the above problem, The Micro-arc Oxidation(MAO) surface treatment technology is used to improve the corrosion resistance of biomagnesium alloy in the vivo environment by growth a layer of ceramic coating formed on the surface of it.First of all, the composition and concentration of silicate electrolyte for MAO are investigated and optimized by spot test and film thickness measurement in this paper. The optimum compositions of silicate electrolyte are: Na2 Si O3: 10 g/L; Na OH: 3 g/L; KF: 8 g/L; glycerol: 0.108 mol/L(10 g/L).And then, the influence of applied voltage and film-formation time on the microstructure and corrosion resistance of coatings formed on Mg-Zn-Zr-Ca novel bio-magnesium alloy has been investigated by MAO treatment. The optimum applied voltage and film-formation time are obtained by the ceramic coatings with good microstructure and corrosion resistance. The experiment was carried out under the constant voltage mode with the optimized silicate electrolyte. The applied voltage is control form 300 to 550 V, respectively. And each voltage set four film-formation times, which is 5, 7, 9, 11 min. Phase composition and microstructure of as-coated samples are analyzed by the x-ray diffraction, energy dispersive x-ray spectroscopy and scanning electron microscopy. And the porosity and average of micro-pore aperture of the surface on the ceramic coatings are analyzed by general image software to comprehensive analysis of microstructure of coatings. The long-term corrosion resistance of as-coated samples is tested in simulated body fluid for 30 days.The results showed that the milky white smooth ceramic coating formed on the Mg-Zn-Zr-Ca bio-magnesium alloy is a compound of Mg O, Mg2 Si O4 and Mg Si O3, and its corrosion resistance is significantly improved comparing with that of the magnesium substrate. In addition, when the MAO applied voltage are 450 V and 500 V and film-formation time are 9 min and 11 min, the surface micro-morphology and the corrosion resistance of as-coated samples are relatively improved. The results provide a theoretical foundation for the application of the Mg-Zn-Zr-Ca novel bio-magnesium alloy in biomedicine. |
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