纯镁表面等离子体电解渗硼与微弧氧化复合膜的制备及耐蚀性

目的 在纯镁表面制备新型复合膜,以提高其耐蚀性.方法 先在硼砂系电解液中对纯镁进行等离子体电解渗硼(PEB)处理,预制表面改性层,然后在硅酸盐系电解液中对其进行微弧氧化(MAO)处理,从而获得PEB+MAO新型复合膜.分别使用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)分析膜层的微观结构、元素分布...

Fabrication and Corrosion Resistance of Hybrid Coatings on Pure Magnesium by Combining Plasma Electrolytic Boronizing with Micro-arc Oxidation

The aim of the research is to prepare a novel hybrid coating on the surface of pure magnesium to improve its corrosion resistance. Pure magnesium was pretreated by plasma electrolytic boronizing (PEB) in borax aqueous solution to obtain the surface modified layer, and then it was processed by micro-arc oxidation (MAO) in silicate-based aqueous solution to fabricate the PEB+MAO novel hybrid coating. The microstructure, element distribution and phase composition of the coatings were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. The anti-corrosion resistance of the coatings was characterized by potentiodynamic polarization curve and electrochemical impedance spectroscope (EIS). The results show that the PEB process of pure magnesium involves four stages, namely ionization, replacement, adsorption and diffusion. The obtained PEB surface modified layer consists of the oxide layer and the diffusion layer. During the growth of the PEB+MAO hybrid coating, instead of simple stacking of layers, overlapping is observed in its thickness direction. In the process of plasma electrolytic saturation, B element infiltrates and forms a layer that reduces the surface chemical activity of pure magnesium substrate but improves its microstructure, thus bringing the corrosion current density of the PEB+MAO hybrid coating down by 3, 2 and 1 orders of magnitude compared with the substrate, single PEB modified layer and single MAO coating, respectively. Meanwhile, according to EIS analysis, the PEB+MAO hybrid coating can provide relatively longer corrosion protection. In addition, the mechanism of formation of PEB surface modified layer and the PEB+MAO hybrid coating is also analyzed, and the physical models are built. In summary, PEB pretreatment has a dramatic effect on the thickness, compactness and chemical composition of the PEB+MAO hybrid coating, thus significantly enhancing the corrosion resistance of pure magnesium. This method for fabrication of the novel hybrid coating is expected to be further applied to magnesium alloys to improve its anti-corrosion ability and bearing capacity.