| SUN Le,MA Ying,LI Qi-hui,WANG Sheng,WANG Zhan-ying.Fabrication and Corrosion Resistance of Hybrid Coatings on Pure Magnesium by Combining Plasma Electrolytic Boronizing with Micro-arc Oxidation[J],50(6):64-76 |
| Fabrication and Corrosion Resistance of Hybrid Coatings on Pure Magnesium by Combining Plasma Electrolytic Boronizing with Micro-arc Oxidation |
| Received:April 08, 2021 Revised:June 09, 2021 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2021.06.006 |
| KeyWord:magnesium plasma electrolytic boronizing micro-arc oxidation surface modification hybrid coating corrosion resistance |
| Author | Institution |
| SUN Le |
State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou , China |
| MA Ying |
State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou , China |
| LI Qi-hui |
State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou , China |
| WANG Sheng |
State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou , China |
| WANG Zhan-ying |
State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, Lanzhou University of Technology, Lanzhou , China |
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| Abstract: |
| 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. |
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