(1) During the entire service life of the galvanize corrugated sheet, the first corrosion that occurs is the oxidation of the galvanized layer on the surface, resulting in white rust. After a long time, the white rust on the surface will further react with impurity gases such as carbon dioxide in the moist air, forming black spots. When the galvanize corrugated sheet is used for a long time and the galvanized layer corrodes more severely, the steel base loses the sacrificial anti-corrosion effect of zinc and begins to oxidize to form red rust. Once the steel base begins to oxidize, the corrosion rate becomes very fast, and the galvanize corrugated sheet ends its life.
(2) In addition, there are two special corrosion conditions of galvanize corrugated sheet called blackening. One is that after the galvanize corrugated sheet is used for a period of time, due to the influence of elements such as lead in the galvanized layer, the matte part of the spangle will become black, and the blackened galvanized layer will still protect the steel base. It only has a certain impact on life span. This situation has been greatly improved after the current suspension of lead and the use of antimony to promote the formation of spangles. Another situation is that the galvanize corrugated sheet is transported. Due to the low coiling tension, the steel strip layers are loose, and the parts of the steel coil contacting the skid will rub against each other and cause oxidation. After the white oxide is rubbed off, the plating Black spots are produced on the surface of the zinc plate, which will destroy the passivation film, thin the galvanized layer, greatly reduce the life of the zinc plate, and affect the appearance.
(3) The corrosion resistance of the galvanize corrugated sheet in a dry environment or a pollution-free environment is very superior. However, in a contaminated environment, the life span will be greatly shortened, and it must be pre-coated into a colored plate before use.
(4) In general, the corrosion of galvanize corrugated sheet is not caused by all the galvanized layers on the surface being uniformly corroded, but the coating is corroded first where the coating is poorly combined with the substrate, causing severe local corrosion and loss of use Performance. From this point of view, the adhesion of the galvanized layer, especially the overall adhesion, is more important than the thickness of the galvanized layer. If the local adhesion of the galvanized layer is not good, even if the galvanized layer is thicker, it will start to rust from the poor adhesion. This is similar to the principle of the bucket, and it is a problem that the galvanizing production technicians must understand.
