The appearance of a bluish-white zinc coating, the standard electrode potential is -0.76V, soluble in acid, alkali-soluble, metal music is amphoteric type. Zinc dry air change hardly occurs, corrosion of zinc critical humidity greater than 70%, in the wet atmosphere and therefore can generate a thin film mainly consisting of basic zinc carbonate with carbon dioxide and oxygen effect, this membrane has a certain inhibition and so on, and zinc sulfide-containing hydrogen sulfide from the reaction of zinc sulfide; zinc chloride susceptible to erosion, it is instability in seawater.
Zinc in an enclosed or poorly ventilated, humid air conditions, when non-metallic materials in contact with the volatile matter (low molecular weight carboxylic acids, aldehydes, phenols, ammonia, etc.), zinc vulnerable to corrosion, loose white corrosion product is generated, commonly known as ” frost. ” Zinc at high temperatures, high humidity, confined conditions, and bakelite, paint, wood volatiles released contacting zinc has a tendency filamentous growth of single crystals, commonly known as “hairy.”
Standard potential than iron zinc negative, in terms of the steel is anodic coating provides reliable electrochemical protection. Use in an industrial atmosphere, rural atmosphere and ocean of the atmosphere can be selected steel products zinc as a protective layer, its relationship with the protective zinc coating life is almost proportional to the thickness. Where industrial air pollution in the atmosphere, zinc coating corrosion better than cadmium plating, at sea or in the sea opposite.
After zinc coating after chromate corrosion resistance can be improved 6–8 times. It is essential for galvanized passivation step. In the passivation film organic dye, can be used for low file protection products — decorative coating.
To reduce the thickness of zinc coating can improve corrosion resistance, at home and abroad adopt the following two measures: First, to improve the quality of the passivation film, such as blue, green, military green, black passivation instead of the conventional rainbow color passivation film , especially in military green passive film corrosion resistant; the second is a thin iron 0.3% – 0.6% Zn-Fe alloy, nickel, or 6% -10% of the Zn-Ni alloy instead of pure zinc coating, corrosion performance improvements more than three times, widely used on cars instead of galvanized steel sheet.
Zinc coating temperature not exceeding 2500C, the temperature deformation of the crystal structure of zinc, brittle, corrosion resistance decreased. There corrosion resistance, heat requirements of the parts is appropriate Zn-Ni alloy layer.
Galvanized electrolyte can be pided into two major categories of basic and weak acid, commonly used at home and abroad Have cyanide zincate zinc cyanide, zinc, galvanized ammonium salts, zinc chloride, zinc, and other sulfate. Domestically, non-cyanide zincate is still the mainstream. In recent years, due to the improved performance of galvanized additives improve, zinc chloride and low cyanide bright zinc rapid development, and ammonium galvanizing continued to decline.
Select the plating bath according to pieces of material, shape, appearance requirements may be, such as stamping small parts and complex parts, in particular the need for auxiliary anode hole or tubular member should use alkaline bath; hydrogen embrittlement sensitive parts is appropriate weak acid zinc plating solution. When the performance of two different bath, the production is very favorable.
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