合金层白点的产生及其对镀锡板耐蚀性的影响

Effect of white point of alloy layer on corrosion resistance of tinplate and its generation

脱去镀锡板的自由锡层后 ,在锡铁合金层的表面目视发现了大量沿轧制方向伸展的白点 ,并且合金层的耐蚀性随着白点数量与覆盖面积的增加而下降。采用扫描电镜 (SEM)观察了合金层的形貌 ,用能谱 (EDS)分析了白点与非白点处的成分 ,结果发现 :白点处的合金层存在空洞 ,且铁的含量高于非白点处的含量。将表面带有大量白点的合金层进行 14d的湿热实验后发现 ,在白点的边缘以及小白点处容易生锈 ,采用原子力显微镜(AFM )观察了锈点处的形貌 ,并解释了发生这一现象的原因。通过实验室模拟和现场数据的分析 ,找出了合金层表面白点产生的原因。

Massive white points outspreading along rolling direction on the surface of Sn-Fe alloy layer was discovered after removing tin coating of tinplates offered by some steel works. Corrosion resistance of alloy layer declines with the increase of amount of white points. Morphologies of alloy layer were observed by SEM, and composition of normal alloy layer and white points were analyzed by EDS. It is found that there are many cavities in the white point and the content of Fe in the white point is more than that in the normal alloy layer. In addition, hot-humidity testing was carried out for some plates whose surface has many white points. After 14 days, there are many rust points occurring at the edge of white points and in the small white points. Morphologies of rust points were observed by AFM. The reason why rust points generates at the edge of white points and in the small white points is discussed. Finally, the reason of generating white point on the surface of alloy layer is found out.