拉应力条件下微弧氧化膜对铝合金腐蚀及电化学行为的影响

为研究在拉应力条件下微弧氧化膜对铝合金腐蚀及电化学行为的影响，采用恒载荷应力环在3.5% NaCl溶液中研究了经微弧氧化（MAO）处理后的7050铝合金（AA7050）应力腐蚀行为。用原位电化学阻抗谱（EIS）的方法评价在拉应力条件下，膜层的腐蚀破坏随浸泡时间的变化，并建立了相应的等效电路模型。结果表明，在3.5% NaCl溶液中，微弧氧化膜在有无拉应力的条件下都可以提高AA7050的耐蚀性和减少AA7050的塑性损失。在400 MPa拉应力条件下，微弧氧化膜的阻抗在应力腐蚀的过程中呈现出先减小后增大，再减小最后趋于稳定的规律；另外，AA7050在有拉应力的条件下，拉应力会促进基体的点蚀形核，提高腐蚀速率，微弧氧化膜的疏松层在拉应力的作用下会失去对基体的保护作用。

Effects of Micro-arc Oxidation Coating on Corrosion and Electrochemical Behavior of Aluminum Alloy Under Tensile Stress

To study the effect of micro-arc oxide coatings on the corrosion and electrochemical behavior of aluminum alloy under tensile stress, stress corrosion behavior of 7050 aluminum alloy (AA7050) treated by micro-arc oxidation (MAO) was studied in a 3.5% NaCl solution using a constant load stress ring.The in-situ electrochemical impedance spectroscopy (EIS) method was used to evaluate the corrosion failure of the coating under the tensile stress condition with the immersion time, and the corresponding equivalent circuit model was established. The results show that the MAO coating can improve the corrosion resistance of AA7050 and reduce the plastic loss of AA7050 in the presence or absence of tensile stress in 3.5% NaCl solution. Under the tensile stress of 400 MPa, the impedance of the MAO coating firstly decreases and then increases during the stress corrosion process, and then decreases and finally stabilizes. In addition, the tensile stress of AA7050 promotes the pitting nucleation and corrosion rate of the matrix under the tensile stress. The loose layer of the MAO coating loses the protection of the matrix under the tensile stress.