It is mainly due to the severe reaction of iron and zinc. The fierce response of the Fe-Zn makes the original coating that was originally composed of the alloy layer and the pure zinc layer to the phenomenon of only the alloy layer and no pure zinc layer. Gray or dark gray is the color of iron zinc alloy. In addition, if the quality of zinc fluid deteriorates, the iron content in the zinc liquid increases, and the pure zinc layer on the surface after galvanized is gray due to iron, causing color difference.
Specific reasons:
1. Plating material contains more carbon, silicon, sulfur, phosphorus and other elements. The electrochemical reactions between iron and zinc are relatively high due to the inert electrode formed by this type of element, which causes the iron zinc reaction to intensify.
2. The content of metal elements such as aluminum in zinc liquid is small, and it cannot effectively suppress its iron -zinc reaction for galvanized steel and other materials.
3. Increased iron content in zinc liquid, which worsen the quality of zinc liquid.
