Defect formation and anode/cathode relationships in underfilm corrosion of heterogeneous aluminium alloys

有机涂层(漆)合金和金属的涂层劣化和膜下腐蚀是一个复杂的过程，取决于许多变量、环境、涂层和基材特性。对于非均质铝合金，情况比钢复杂得多，而且其机理细节还没有完全了解。这些合金具有许多不同的金属间化合物相，它们的电化学性质彼此不同，并且与铝基不同。后者不能很好地支持阴极反应，而一些金属间化合物相则支持。本项目的目的是阐明这类合金涂层失效的机理细节，特别是金属间化合物相对膜下腐蚀初始阶段的影响、电偶对腐蚀扩展的作用、局部阳极和阴极的出现、腐蚀产物的作用以及与腐蚀过程有关的涂层劣化。一种主要的方法是共聚焦激光扫描显微镜，用于三维原位监测涂层下形成的腐蚀计量，并使用结合到涂层中的离子敏感荧光染料-在合金表面和涂层内分层期间的化学变化。此外，还将使用石英晶体微天平测量来研究涂层的性能，使用局部化的电化学阻抗谱来描述膜下腐蚀中通常出现的复杂的阻抗响应，以及(表面)分析技术来研究腐蚀产物和铜的复制的作用。在此基础上，建立了铝合金涂层失效的详细模型。

Coating deterioration and underfilm corrosion of organically coated (lacquered) alloys and metals is a complicated process depending on many variables, environment, coating, and substrate properties. For heterogeneous aluminum alloys, the situation is much more complex than for steel, and the mechanistic details are not fully understood. These alloys have numerous intermetallic phases differing in their electrochemical properties among each other, and from the aluminum matrix. The latter does not support cathodic reactions very well, whereas some of the intermetallic phases do. The aim of this project is to elucidate the mechanistic details of coating failure on such alloys, especially with respect to the influence of intermetallic compound phases on the initial stages of underfilm corrosion, the role of galvanic coupling on the corrosion propagation, the occurrence of local anodes and cathodes, the role of corrosion products and the coating deterioration linked to the corrosion processes. One major method is Confocal Laser Scanning Microscopy for three-dimensional in-situ monitoring of corrosion metrology developing underneath the coating and - using ion-sensitive fluorescent dyes incorporated into the coating - chemical changes during delamination at the alloy surface and within the coating. In addition quartz crystal microbalance measurements for the study of coating properties, localized electrochemical impedance spectroscopy to delineate the usually complex impedance response seen in underfilm corrosion, and (surface) analytical techniques to study the role of corrosion products and copper replating will be applied. Based on the results, detailed models for coating failure on the aluminum alloys shall be developed.