Why does the surface of hot-dip galvanized sheet turn black?
Reasons why hot-dip galvanized sheets turn black:
a. The purity of the hot-dip galvanized layer is insufficient, and metal residues form galvanic reactions on the surface of the zinc. When it is beneficial to hydrogen evolution, it is easy to cause black spots on the surface of the zinc layer.
b. When the copper, iron, arsenic and other residues in the hot-dip galvanizing layer are high in content, these residues will appear black after passivation.
c. Insufficient treatment of contaminants on the surface of the entire panel results in the formation of sediment, which prevents some areas from being galvanized, causing problems with the hot-dip galvanized layer and making it easy to fall off, resulting in black spots.
d. Missing plating occurs during hot-dip galvanizing, and it is very easy to produce black spots during the post-processing process.
e. The hot-dip galvanizing solution is mixed with sediment or small ash (carbon or carbon substances), which adheres to the surface of the zinc layer or is in the zinc layer, and is strongly integrated with the zinc layer. Black spots can be seen on finished galvanized steel panels.
f. Cavitation black spots. Caused by rough work during transportation and accumulation.
