航空铝合金涂层体系加速老化试验前后电化学阻抗变化

采用电化学阻抗谱(EIS)技术,选用目前飞机上使用的7B04铝合金/锌黄丙烯酸聚氨酯有机涂层体系,对其在加速老化试验过程中的电化学阻抗变化进行了原位测试,分析了其失效的特征.研究表明,加速老化试验前,7B04铝合金锌黄丙烯酸聚氨酯涂层中的缺陷较少,涂层可以很好地将腐蚀性介质阻挡在外,保护金属基体免受腐蚀破坏,此时涂层相当于1个纯电容.加速老化试验后,水很快就能进入涂层内部,但涂层内防腐蚀颜料锌铬黄离子遇水发生水解反应的产物能将基体钝化,保护基体免受腐蚀,经过335 h即1个周期电解液已渗透到达涂层/基底的界面,并在界面区形成腐蚀反应微电池后,测得电化学阻抗谱表现为2个时间常数.划痕处金属的腐蚀反应与划痕周围涂层内锌铬黄离子的水解反应同时进行,加速老化试验进行1 008 h即3周期后,电化学阻抗谱上出现感抗现象,在低频时相角出现负值,这是由于锌铬黄离子的水解产物能将金属基体钝化,而钝化膜此时处于点蚀诱导期.感抗现象在加速老化试验进行了1 344 h即4周期后消失,说明此时钝化膜已经穿孔,点蚀进入发展期,并有腐蚀产物生成.

Electrochemical Impedance Varieties of Zinc Yellow Polypropylene Coated Aluminum Alloy Used in Aircraft During the Accelerated Degradation Test

The electrochemical impedance varieties of zinc yellow polypropylene coated aluminum alloy 7B04 used in aircraft during accelerated degradation test are studied using electrochemical impedance spectroscopy(EIS),and the characteristics of its corrosive failure are also investigated.It has been found that the zinc yellow polypropylene coating has little flaws and acts as a pure capacitance before the degradation test.But water can quickly permeate into the coating after exposure to the test.However the anticorrosive pigment zinc yellow ion can hydrolyze and the production can make aluminum alloy passivate,then prevent the base from corroding.After 336 h of exposure to the test,water reaches the aluminum alloy/paint interface,and forms corrosive micro-cell,and the impedance spectroscopy shows two time constants.For the scratched samples,the reaction of metal corrosion and the hydrolyzation of zinc yellow ion can occur simultaneously.The impedance spectroscopy indicates inductance after 1 008 h of exposure,that is because the hydrolyzation production can passivate the corrosive active sites,and the passivation layer is just in the pitting corrosion inducing stage.The inductance disappears after 1 344 h of exposure and the passivation layer has pitting corrosion.