Features of hot sales construction galvanized square ASTM Q195 steel tube galvanized
The appearance of zinc coating is bluish-white, and the standard electrode potential is -0.76V. It is easily soluble in acid and soluble in alkali. It is a curved amphoteric metal. There is almost no change in zinc dry air, and the critical humidity of zinc corrosion is greater than 70%. Therefore, in a humid atmosphere, it can interact with carbon dioxide and oxygen to form a film mainly composed of basic zinc carbonate, which has certain corrosion inhibition. Zinc reacts with sulfides such as hydrogen sulfide to form zinc sulfide; zinc is easily corroded by chloride ions, so it is unstable in seawater.
When zinc is in contact with volatiles of non-metallic materials (low molecular carboxylic acid, aldehyde, phenol, ammonia, etc.) under airtight or poor ventilation and humid air conditions, zinc is easily corroded, resulting in white loose corrosion products, commonly known as "" Hoarfrost". When zinc comes into contact with volatiles released from bakelite, paint and wood under high temperature, high humidity and airtight conditions, zinc has a tendency to grow filamentous single crystals, commonly known as "long hair".
The standard potential of zinc is negative than that of iron, and it is an anodic coating for steel, which can provide reliable electrochemical protection. Zinc can be selected as a protective layer for steel products used in industrial atmosphere, rural atmosphere and marine atmosphere, and its protective life is almost proportional to the thickness of the zinc layer. In the atmosphere with industrial waste gas pollution, the corrosion resistance of zinc coating is better than that of cadmium coating, and the opposite is true in sea or sea water.
After the hot sales construction galvanized square ASTM Q195 steel tube zinc coating is passivated by chromate, the corrosion resistance can be improved by 6--8 times. Therefore, galvanizing passivation treatment is an essential step. Organic dyeing on passivation film can be used for protection of low-profile products---decorative coating.
In order to reduce the thickness of the zinc coating and improve the corrosion resistance, the following two measures are adopted at home and abroad: one is to improve the quality of the passivation film, such as using blue, green, military green, black passivation instead of the conventional iridescent passivation film , especially the military greening passivation film has the best corrosion resistance; the second is to replace pure zinc with a thinner Zn-Fe alloy containing 0.3%--0.6% iron, or a Zn-Ni alloy containing 6%-10% nickel Coating, the corrosion resistance is improved by more than three times, and it is widely used in automobile steel plate instead of galvanized.
The hot sales construction galvanized square ASTM Q195 steel tube use temperature of zinc coating should not exceed 2500C, at this temperature, the zinc crystal structure will deform, become brittle, and the corrosion resistance will decrease. Parts with corrosion resistance and heat resistance requirements should use Zn-Ni alloy layer.
The hot sales construction galvanized square ASTM Q195 steel tube galvanizing electrolyte can be divided into two categories: alkaline and weakly acidic. Commonly used at home and abroad are cyanide zincate, cyanide zinc, ammonium salt, chloride zinc, sulfate zinc and so on. Domestically, cyanide-free zincate galvanizing is still the mainstream. In recent years, due to the improvement of the performance of galvanizing additives, chloride galvanizing and low-cyanide bright galvanizing have developed rapidly, while ammonium salt galvanizing continues to decline.
The choice of plating solution depends on the material, shape and appearance requirements of the plated parts, such as stamping small parts and complex parts, especially for deep holes or tubular parts that require auxiliary anodes. Alkaline plating solution should be used; parts sensitive to hydrogen embrittlement should be used. Weak acid zinc plating solution. When two kinds of baths with different properties are used, it is very beneficial to production.