08
2020
Corrosion resistance of galvanizing steel plate
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After the galvanizing steel plate is galvanized, the surface properties are very different from ordinary steel plates. In terms of anti-corrosion coating, most paint coatings can be applied to ordinary steel plates, but the anti-corrosion coating of galvanizing steel plate is a problem. frequent. The main reason is that the surface of the galvanizing steel plate is smooth, and the adhesion of most paints cannot achieve a good effect, resulting in the peeling of the paint film, which cannot play a protective role.
With the development of galvanizing process and the use of high-performance galvanizing brighteners, galvanizing has entered protective-decorative applications from purely protective purposes. There are two types of zinc plating solutions: cyanide baths and cyanide-free baths. The cyanide bath is divided into microcyanide, low cyanide, medium cyanide, and high cyanide. Cyanide-free baths include alkaline zincate baths, ammonium salt baths, sulfate baths, and ammonia-free chloride baths. The cyanide zinc plating solution has good uniform plating ability, and the obtained coating is smooth and delicate, and has been used for a long time in production. However, due to the high toxicity of cyanide and serious environmental pollution, low-cyanide, micro-cyanide and cyanide-free zinc plating solutions have been used in recent years.
The standard electrode potential of zinc is low, and the galvanized layer on the iron base is an anodic coating in a general corrosive medium, which can effectively slow down the corrosion of the steel substrate. obvious advantage. The flat and dense galvanizing layer of galvanizing steel plate can be protected by the corrosion resistance of zinc, and the incision and local damaged area of the coating can be protected by sacrificial anode (zinc layer) to reduce the corrosion rate. In addition, the non-toxic, inexpensive and excellent protective properties of zinc coating make the galvanizing process play an important role in anti-corrosion technology.
1. Corrosion process of galvanizing steel plate
Generally, the corrosion process of galvanizing steel plate is divided into 4 stages, namely: the stage of coating corrosion; the stage of sacrificial corrosion protection to the substrate after the local disappearance of the coating; the stage of galvanizing corrosion products to inhibit the corrosion of the substrate; the corrosion stage.
2. Factors of corrosion resistance of galvanized layer
The thickness of the galvanized layer is one of the most important factors in determining the corrosion resistance of the steel substrate. According to the Swedish anti-corrosion research, the corrosion resistance of the galvanized layer is the most reasonable when the thickness of the galvanized layer is 7-10mm. When it is greater than 60g/m2, it has better resistance to corrosion under the film. At the same time, the corrosion resistance of galvanizing steel plate in actual use depends not only on the galvanizing steel plate itself, but also on the processing state and use environment of the galvanizing steel plate. These three factors can also become the corrosion triangle of the galvanizing steel plate.
