Abstract In order to study the effect of defects on the corrosion behavior of MAO coatings, global electrochemical method including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) was used to measure the corrosion resistance of MAO coatings. Local electrochemical measurements including local impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET) were used to study the local corrosion mechanism. The confocal microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the microstructure and phases of the samples. Results of global electrochemical measurement demonstrate that the scratches cause the reduction of the impedance and the increase of the corrosion current density. LEIS results show the impedance value distribution of the coating with the scratch. With the changes over time, the minimum impedance value of the scratch decreases first and then increases from the third hour. SVET results show the corrosion current density distribution of the scratched coating. The maximum corrosion current density at the scratch increases first and then decreases. The results of local electrochemical measurements show that the corrosion rate at the scratch decreases when the reaction lasted 3 h. Confocal microscopy found that the scratch is expanding with increasing time, and the depth and cross-sectional area of the coating is 5 times deeper and 10 times larger than that of 7075Al with scratch at the first 6 h. The 6-day immersion test proved that the scratch coating still has the protective effect on the substrate. The main corrosion product is Al(OH)3. A physical model reflecting the mechanism of the scratch propagation and the formation of the corrosion product film is proposed.

中文翻译：

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MAO涂层7075铝合金局部腐蚀行为及机理研究

摘要 为了研究缺陷对微弧氧化涂层腐蚀行为的影响，采用动电位极化（PDP）和电化学阻抗谱（EIS）等全局电化学方法测量微弧氧化涂层的耐腐蚀性能。包括局部阻抗谱（LEIS）和扫描振动电极技术（SVET）在内的局部电化学测量被用来研究局部腐蚀机制。采用共聚焦显微镜、扫描电子显微镜(SEM)和X射线衍射(XRD)对样品的微观结构和物相进行观察。整体电化学测量结果表明，划痕导致阻抗降低和腐蚀电流密度增加。LEIS 结果显示了带有划痕的涂层的阻抗值分布。随着时间的推移，划痕的最小阻抗值从第 3 小时开始先减小后增大。SVET 结果显示了划痕涂层的腐蚀电流密度分布。划痕处的最大腐蚀电流密度先增大后减小。局部电化学测量结果表明，当反应持续 3 h 时，划痕处的腐蚀速率降低。共聚焦显微镜发现划痕随着时间的增加而扩大，涂层的深度和横截面积比带划痕的 7075Al 在前 6 小时深 5 倍，大 10 倍。6天的浸泡试验证明划痕涂层对基材仍有保护作用。主要腐蚀产物是Al(OH)3。提出了反映划痕传播机制和腐蚀产物膜形成的物理模型。