Galvanizing refers to the surface treatment technology that coats a layer of zinc on the surface of metal, alloy or other materials to play the role of beauty and rust prevention. The mainmethod used is hot-dip galvanizing.
Zinc is soluble in acid and alkali, so it is called amphoteric metal. Zinc hardly changes in dry air. In humid air, a dense basic zinc carbonate film is formed on the zinc surface. In the atmosphere containing sulfur dioxide, hydrogen sulfide and marine, the corrosion resistance of zinc is poor, especially in the atmosphere containing organic acid at high temperature and high humidity, the zinc coating is easily corroded.
The standard electrode potential of zinc is -0.76V. For the steel substrate, the zinc coating is an anodic coating, which is mainly used to prevent the corrosion of steel, and its protective performance has a great relationship with the thickness of the coating. The protective and decorative properties of zinc coating can be significantly improved after passivation treatment, dyeing or coating with light protectant.
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.