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由于结构和成分的影响,覆有微弧氧化涂层的AZ91D镁合金的极化曲线有多种不同的表现形式.事实上,覆有微弧氧化涂层的AZ91D镁合金在NaCl溶液中的极化曲线行为不仅与涂层的主要组成和微观结构有关,也与极化曲线测试条件,如氯离子浓度、溶液pH值、阴极极化程度和样品的暴露面积有关.由于微弧氧化涂层的不稳定性,这些因素通过改变氧化涂层的组成和微观结构,继而影响极化曲线的形状.本文用傅里叶变换显微红外成像和对应的光学照片研究了氧化涂层的成分和结构的变化.结合物理表征,我们提出一个模型,用以阐明微弧氧化涂层组成和结构在NaCl溶液中的变化.对于浸泡在NaCl溶液中的AZ91D微弧氧化涂层,阳极溶解和阴极还原反应的速控步骤分别是传质过程和电荷转移过程.所以从极化曲线上拟合出来的腐蚀电流密度不能准确反映腐蚀速率,而且误差也难以避免.
Due to the influence of structure and composition, the polarization curve of AZ91D magnesium alloy covered with micro-arc oxidation coating has many different manifestations.In fact, the AZ91D magnesium alloy coated with micro-arc oxidation coating in NaCl solution The behavior of the curve is not only related to the main composition and microstructure of the coating, but also to the polarization curve test conditions such as the chloride ion concentration, the solution pH, the degree of cathodic polarization and the exposed area of the sample. Instability, these factors affect the shape of the polarization curve by changing the composition and microstructure of the oxide coating.In this paper, the composition and structure of the oxide coating were studied by Fourier transform microscopy and corresponding optical photographs In the light of the physical characterization, we present a model to clarify the composition and structure of microarc oxidation coatings in NaCl solution.For the AZ91D microarc oxidation coatings immersed in NaCl solution, the anodic dissolution and cathodic reduction reactions The speed control steps are the mass transfer process and the charge transfer process respectively, so the corrosion current density fitting from the polarization curve can not accurately reflect the corrosion rate, and the error is hard to avoid.