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There was a great attraction to apply magnesium alloy as a biomedical material due to its biodegradable feature and suitable mechanical properties. In order to further improve the wear resistance performance of magnesium alloy, a micro-arc oxidation (MAO) coating containing MgSiO3 was generated on the suface of Mg-Zn alloy. The surface characterization by SEM, XRD and EDS showed that a rough and porous reaction layer with major composition of O, Mg and Si was formed on the surface of Mg-Zn alloy. The result showed that the MAO coating significantly enhanced the wear resistance of Mg-Zn alloy and friction rotate rate had not obvious on the friction coefficient of the MAO coating. Introduction The magnesium alloy had been well known as a new kind of biomedical material, possessing excellent mechanical properties with high strength, appropriate density and elastic modulus properties, which was similar to that of natural bones which could effectively reduce the “stress sheltering” for other metallic bone implants from the beginning of 21 century. Unfortunately, it was difficult for the rapid degradation rate of magnesium alloy to meet the requirement of rigid internal bixation, meanwhile, accompanied by the release of hydrogen gas upon degradation. So those above factors affected their clinical applications to some degree Surface modification technology was usually applied on magnesium and its alloys to obtain a desirable corrosion property for biomedical applications. At present, a variety of surface coating techniques had been applied on the biodegradable magnesium alloys to decrease the initial degradation rate, which included ion implantation, chemical conversion, electrochemical deposition, anodization, micro-arc oxidation, etc. compared with above technology, the micro-arc oxidation method (MAO) could form a thick and hard coating, which possessed excellent abrasive resistance and good bonding with the substrate. In this paper, KF and EDTA-2Na were selected as additives in Na2SiO3–NaOH solution to prepare the ceramic coatings by micro-arc oxidation technology. MAO coatings containing MgSiO3 phase were fabricates on the surface of the magnesium alloys and microstructure was analysized. The effect of the friction rotating rate on the the friction behaviors were investigated in details. Materials fabrication and characterization The detailed preparation procedure of the MAO coating was describedas follows. The hot extrusion Mg-Zn alloy was utilized as substrate materials. Before the MAO coatings, the specimens were cut in the sizes of 10mm×10mm×5mm. Surfaces of the investigatived Mg alloy specimens were ground to grids of 600, 1200 and 2000 by SiC papers and cleaned in distilled water and acetone. Then a silicate containing electrolyte (16 g/L Na2SiO3, 6g/L NaOH, and 4g/L KF) was International Conference on Materials, Environmental and Biological Engineering (MEBE 2015) © 2015. The authors Published by Atlantis Press 1037 adopted for the MAO treatment. The alloy specimen was taken as the working electrode and the counter electrode was the stainless steel container. The voltage, work frequency, duty cycle and preparation time were 320 V, 1000 Hz, 20% and 10 min, respectively. After MAO treatment, the samples were soaked thoroughly in distilled water and dried in air. The wear properties of the composites was measured by SFT-2M pin on disk wear tester. The abrasion counterpart was made of steel of GCr15 and rotating radius was 3mm and load was 300g. The rotating rate was different as 300rpm, 600rpm, 900rpm and 1200rpm, which were nominated as R300, R600, R900 and R1200. The phase composition was analyzed using X-ray diffractometer (XRD, D/max2500) with Cu Kα radiation. The microstructure of the MAO coating was observed on a scanning electron microscopy (HITACHI/S-3700). The chemical composition of the coating was determined by the energy dispersive spectrum (EDS, Oxford 300) analysis. Results and discussion The XRD pattern of MAO coating of the Mg-Zn alloy were illustrated in Fig.1. In the matrix specimen of the Mg-Zn alloy, the Mg phase was considered as the main phase, the main diffraction peak was consistent with Mg (No.65-3365#). While after MAO process,the MgO (No.45-0946#) and MgSiO3 (No.19-0768#) phase was detected as the second trace phase, meanwhile the diffraction peak of Mg phase also can be observed. Based on the above results, we can draw to a conclusion that the MgO and MgSiO3 phase can be formed during the MAO process. Fig.1 XRD pattern of MAO oxidation coating of the Mg-Zn alloy The surface morphology and energy spectrum of MAO coating of the Mg-Zn alloywas illustrated in Fig.2. Fig.2(a) and (b) represented high magnification image and energy spectrum of spot “+” in Fig.2a). According to the Fig.2, the pore was uniform and the surface was smooth. It was interesting that micro cracks with appreciable quantity can not be observed. It was noted that more micro cracks can be found from the MAO coating from the previous reports. From this viewpoint, the application of appreciable surface modifier could decorate micro-structure of MAO coating, so it played an important role on the friction properties of the Mg-Al-Y alloy. The energy spectrum of spot “+” in inset of Fig.2(b) was analysed and Mg, Si and O element can be detected. The O and Si element were introduced into the oxide coating surface of the Mg-Zn alloy by the MAO methods. Fig.2 The surface morphology and energy spectrum of the MAO coating specimen

Fabrication of the MAO coating on Mg alloy and Friction Behaviors Analysis