Zinc electroplating: zinc is stable in dry air and changes little. A white film of zinc oxide or carbon zinc carbonate is formed in moist air. This dense film will prevent further corrosion. Therefore, the galvanizing layer is used for the spring corrosion protection under general atmospheric conditions. Zinc coating should not be used for all springs that are in contact with solutions such as sulfuric acid, hydrochloric acid and caustic soda, as well as springs that work in humid air such as sulfur trioxide.Generally, passivation of galvanized coating can improve the protective performance of coating and increase the appearance of coating.· cadmium electroplating: in the atmosphere of sea or high temperature, and the spring in contact with sea water, and in the spring in 70 pens of hot water, cadmium is relatively stable and has strong corrosion resistance. Compared with zinc coating, cadmium coating is brighter and more beautiful, soft and more plasticity than zinc coating. However, cadmium is rare, expensive, and toxic to the environment. As a result, use is limited. Therefore, most of the springs used in the aviation, navigation and electronics industries only use cadmium plating as a protective layer.In order to improve the corrosion resistance of cadmium coating, passivation can be carried out after plating. The thickness of zinc and cadmium coating determines the level of protection. Generally, the thickness should be selected according to the working environment. The thickness of the galvanizing layer is recommended to be selected within the range of 6-24 team m. Cadmium plating thickness is recommended in the range of 6-12dlm.