覆有微弧氧化涂层的AZ91D镁合金在氯化钠溶液中的极化行为(英文)

Polarization Behavior of Magnesium Alloy AZ91D with Micro-Arc Oxidation Coating in NaCl Solution

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.

The polarization curves of magnesium alloy AZ91D with a micro-arc oxidation （MAO） coating showed several typical patterns caused by differences in the composition and structure of the coating.The pattern of the polarization curve of magnesium alloy AZ91D with a MAO coating depends on the primary composition and structure of the MAO coating and many experimental factors,such as the concentration of chloride ions,pH of the electrolyte,degree of cathodic polarization,and the exposed area of the specimen.These factors change the pattern of polarization curve of magnesium alloy AZ91D with MAO coating by affecting the main composition and structure of the MAO coating because of its instability in aqueous solution.Compositional and structural changes in the MAO coating on magnesium alloy AZ91D were investigated by Fourier transform infrared microscopic mapping and the corresponding optical photographs,respectively.A model was proposed to describe the transformation of the MAO coating in aqueous NaCl solution.For magnesium alloy AZ91D with a MAO coating immersed in NaCl solution,the rate determining steps of the anodic and cathodic reactions are the mass diffusion and charge transfer steps,respectively.As a result,the corrosion current density fitted from the polarization curve is not an accurate corrosion rate.