电压对纯镁微弧氧化膜层电化学腐蚀行为的影响

采用循环伏安(CV)、动电位极化(Tafel)和电化学阻抗谱(EIS)技术、结合纯镁微弧氧化膜微观形貌,研究电压对膜层电化学腐蚀行为的影响.结果表明:电压对膜层耐蚀性影响显著,随着电压升高,膜层耐蚀性增强,这是因为较厚的膜层厚度为抵御腐蚀介质的侵蚀提供了良好的物理屏障.在整个腐蚀试验过程中,高电压下制备的膜层经历三个阶段:腐蚀介质逐渐渗入膜层,腐蚀介质渗透膜层到达膜基面侵蚀基体,腐蚀产物填充微孔和微裂纹等缺陷.相比而言,低电压下制备的膜层随着浸泡时间的延长,膜层外部疏松层和内部致密层的电阻均逐渐减小,致使耐蚀性降低,最终膜层完全失效.

Effects of voltage on electrochemical corrosion behavior of micro-arc oxidation coatings

The effects of voltage on the electrochemical corrosion behavior of micro-arc oxidation (MAO) coatings formed on pure magnesium were studied by using cyclic voltammetry (CV), potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy (EIS). SEM was adopted to characterize microstructure of the coatings. The results show that the voltage has significant effects on corrosion resistance of the coatings. With increase of voltage, the corrosion resistance of the coatings gets improved. This may be attributed to the coating's thicker thickness which may provide a good physical barrier against the erosion of the corrosion medium. During the whole corrosion process, the coating prepared in the high voltage experiences three stages: the corrosion medium gradually infiltrates into the coating, then corrosion medium penetrates the coating to the interface between the coating and the substrate, and eventually corrosion products fill into defects such as micropores and microcracks. In contrast, for coatings prepared under low voltage, the electric resistance of both loose layer out of the coating and dense part in the core of the coating decreases gradually with the immersion time prolonging. This results in the corrosion resistance of the coating decreasing, and finally the coating fails completely as a result.