杯突变形对热镀锌合金化镀层耐腐蚀性的影响

Effect of cupping deformation on corrosion resistance of galvannealed coating

测试了不同变形量热镀锌合金化镀层在3.5wt%NaCl溶液中的腐蚀行为,并用SEM观察了镀层腐蚀前后的表面形貌。结果表明,在杯突变形初始阶段,阻抗值下降幅度较大,随后趋于平缓;当变形量为5 mm时,GA镀层表面的腐蚀电流达到最大值,腐蚀最严重。此时,浓差极化效应最弱,镀层表面裂纹缝隙内的各相和基体发生阳极反应,裂纹外部边缘镀层发生阴极反应。随着变形量的增加,阳极和阴极反应同时在裂纹内的各相和基体上进行。腐蚀产物粘附在裂纹内部,增大了溶液的扩散阻力,降低了腐蚀速率。

Corrosion behavior of different deformation galvannealed coatings in 3.5wt% NaCl solution was tested, and surface morphology of the coatings was observed by SEM. The results show that the resistance value decline clear at the initial stage of the cup drawing test, and then tending towards stability. The corrosion current density on the surface of GA coating reach the maximum value and corrosion is most serious when cupping deformation is 5 mm. Meanwhile, the concentration polarization effect is the weakest, anodic reaction is only taken place on the substrate and various phases under the cracks of GA coating, cathodic reaction ts taken place on the outside of cracks. Anodic reaction and cathodic reaction are taken place on the substrate and various phases simultaneously with the degree of deformation increased. The rate of corrosion will decrease because of the corrosion product adhering in the cracks and the diffusion resistance of solution increases.