Corrosion of Carbon Steel under Epoxy-varnish Coating Studied by Scanning Kelvin Probe

The corrosion behavior of partly coated carbon steel was investigated by salt spray test and scanning Kelvin probe （SKP） in order to understand the long-term corrosion behavior of coated carbon steel in marine atmosphere environment. The localized corrosion was accurately characterized by SKP in both coated and uncoated regions. The SKP results showed that Volta potential varied with the test time, and the more the corrosion products, the more positive the potential. The borderline between coated and uncoated regions of partly coated steel shifted towards the coated side with the increasing of test time. The coating disbonding rate could be determined according to the shift of potential borderline measured by SKP. The corrosion mechanism of partly coated steel in NaCl salt spray was discussed according to the potential maps and corrosion morphologies.

AZ91D镁合金电偶腐蚀的扫描开尔文探针原位表征

AZ91D镁合金在潮湿、含C l-大气环境中会发生严重的电偶腐蚀。对AZ91D镁合金与Q235碳钢偶接试样在中性盐雾条件下进行了电偶腐蚀试验,利用扫描开尔文探针技术(SKP)原位测量了不同盐雾试验时间后两偶合件表面伏打电位的变化规律。结果表明:由于AZ91D镁合金与Q235碳钢偶接试样存在较大的伏打电位差(约为-1.14 V),在盐雾试验初期阶段,AZ91D镁合金的电偶腐蚀效应仍然十分显著,又由于镁合金的电偶电流作用距离有限,此阶段腐蚀主要发生在偶接界面AZ91D镁合金一侧附近区域,Q235碳钢得到了保护且并没有发生明显的腐蚀;由于AZ91D镁合金在盐雾中生成的腐蚀产物对镁合金基体有一定的保护作用,AZ91D镁合金覆盖腐蚀产物区域与镁合金基体之间存在较大的伏打电位差(-1.11^-1.54 V),这将促进AZ91D镁合金未腐蚀区域进一步腐蚀;随着盐雾试验时间的延长,腐蚀由偶接界面向AZ91D镁合金试样一侧发展,其电偶腐蚀效应逐渐降低。