飞机用7B04铝合金缝隙腐蚀试验及仿真研究

目的开展飞机用7B04铝合金缝隙腐蚀仿真研究,理解缝隙腐蚀机理,找出影响缝隙腐蚀的关键因素。方法分析缝隙腐蚀类型,开展缝隙腐蚀试验,建立缝隙腐蚀数学模型,选择合适的边界条件,利用有限元法进行仿真计算。结果缝隙内pH值分布计算结果与试验测量值一致,缝隙口与外部液体/大气连接时,缝隙内溶液分别呈酸性或碱性。缝隙口溶液电势较低,缝隙口附近的铝合金腐蚀较快,含Al腐蚀产物多集中在缝隙口附近。缝隙宽度在0.1~0.3 mm范围内变化不影响铝合金腐蚀速率;缝隙深度增加,缝隙口与底部溶液电势差增大,铝合金腐蚀面积增大,但铝合金最大腐蚀电流密度不变。电位升高,缝隙内铝合金的腐蚀加剧,电位提高10 m V,腐蚀24 h后缝隙内铝合金界面的腐蚀电流密度增加59倍,Al(OH)_2Cl的最大浓度为自然电位下的30倍。结论缝隙腐蚀主要受缝隙外部阴极还原反应影响,电位对铝合金缝隙腐蚀的影响最大,飞机结构中应避免高电位材料同铝合金直接接触。

Crevice Corrosion Experiment and Simulation Study of 7B04 Aluminum Alloy for Aircraft

Objective To develop the crevice corrosion simulation study of 7B04 aluminum alloy for aircraft, understand the mechanism of crevice corrosion, and find out key factors affecting crevice corrosion. Methods Types of crevice corrosion were analyzed, crevice corrosion tests were developed, a mathematical crevice corrosion model was established, proper boundary conditions were selected, and simulating calculation was performed with the finite element method. Results The calculation result of pH value distribution in the crevice was consistent with test measurement value, and when crevice mouth communicated with external liquid/atmosphere, the solution in the crevicewas in acidic or in alkaline respectively. The solution at the crevice mouth was relatively low in potential, the aluminum alloy near the crevice mouth corroded relatively fast, and most Al-containing corrosion products were concentrated near the crevice mouth. The corrosion rate of the aluminum alloy was not affected by change of the crevice width in the range of 0.1~0.3 mm; if the depth of the crevice was increased, the solution potential difference between the crevice mouth and the bottom was increased, the corrosion area of the aluminum alloy was increased, but the maximum corrosion current density of the aluminum alloy was unchanged. If the potential rose, corrosion of the aluminum alloy in the crevice was intensified, the potential was increased by 10 mV, the corrosion current density of aluminum alloy interface in the crevice after 24 h corroding was increased by 59 times, and the maximum concentration of Al(OH)2Cl was 30 times that of Al(OH)2Cl under natural potential. Conclusions Crevice corrosion is mainly affected by cathode reduction reaction outside the crevice. The potential has a maximum influence on crevice corrosion of aluminum alloy. High-potential materials should be prevented from making direct contact with aluminum alloy in the aircraft structure.