AZ91D镁合金电偶腐蚀的扫描开尔文探针原位表征

In-Situ Analysis of Galvanic Corrosion Behavior of AZ91D Magnesium Alloy by Scanning Kelvin Probing

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。

Galvanic corrosion tests of AZ91D Mg alloy/Q235 carbon steel couple were carried out under neutral salt spray condition.The variations of the surface Volta potentials of the two coupling parts at different corrosion durations were in-situ measured using scanning Kelvin probing(SKP) technique.It was found that because AZ91D Mg alloy and Q235 carbon steel had a large potential difference of about-1.14 V,AZ91D Mg alloy had a significant galvanic effect in the early stage of salt spray test.The galvanic current of Mg alloy only activated in a limited range,and corrosion mainly occurred near the interface region on the side of AZ91D Mg alloy,so Q235 carbon steel was effectively protected.The corroded products of Mg alloy during salt spray test were able to protect the Mg alloy substrate to a certain degree.However,there existed a large Volta potential difference(-1.54^-1.11 V) between the corrosion-product-covered region and exposed Mg alloy substrate,resulting in accelerated corrosion of the exposed region.With the increase of salt spray test time,the corrosion developed from the interface to the AZ91D Mg alloy,and the galvanic corrosion effect was gradually reduced.