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为分析镁合金表面膜的活性位置,建立起镁负极的点蚀破坏与电化学特性的关联性,本文采用循环伏安和电化学阻抗技术研究了AZ镁合金在MgSO_4溶液中的点蚀行为,从电解质浓度、电位扫描速度、阴极极化角度探讨腐蚀膜对镁合金点蚀的影响。电化学阻抗谱由两个连续容抗弧构成,其电荷转移电阻和膜电阻均随MgSO_4溶液浓度增大而减小,当MgSO_4溶液浓度为1.5 mol/L时,AZ31B合金表面膜阻抗最低,容易发生点蚀。扫描速率从3.3 m V/s下降至0.17 m V/s时,AZ63合金点蚀滞后环面积先增加后减小,击穿电位负移。控制阴极极化起始电位负移,则击穿电位降低,滞后环的面积增加,AZ镁合金的点蚀倾向变大;而在阴极过电位下停留可降低表面膜的腐蚀破坏程度,有利于抑制镁合金点腐蚀的发展。
In order to analyze the active sites of magnesium alloy surface membrane and establish the correlation between pitting corrosion and electrochemical properties of magnesium negative electrode, the pitting corrosion behavior of AZ magnesium alloy in MgSO_4 solution was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The effect of corrosion film on the pitting corrosion of magnesium alloy was discussed from the aspects of electrolyte concentration, potential scanning speed and cathodic polarization. The electrochemical impedance spectroscopy consists of two continuous capacitive arcs. The charge transfer resistance and the membrane resistance decrease with the increase of the concentration of MgSO_4 solution. When the concentration of MgSO_4 solution is 1.5 mol / L, the surface impedance of AZ31B alloy is the lowest, which is easy Pitting occurs. When the scan rate decreases from 3.3 mV / s to 0.17 mV / s, the pitting hysteresis loop area of AZ63 alloy firstly increases and then decreases, and the breakdown potential shifts negatively. When the negative initial potential of cathodic polarization is controlled, the breakdown potential decreases and the area of the hysteresis loop increases. The pitting corrosion tendency of AZ magnesium alloy becomes larger. However, staying at cathode overpotential can reduce the corrosion damage of the surface film, Inhibit the development of pitting corrosion of magnesium alloy.