What are the differences between zinc plating, cadmium plating, chromium plating, and nickel plating of steel pipe and steel bar?
Characteristics: Zinc is relatively stable in dry air and is not easily discolored. In water and humid atmospheres, it reacts with oxygen or carbon dioxide to form oxides or alkaline zinc carbonate films, which can prevent zinc from continuing to oxidize and play a protective role.Zinc is highly susceptible to corrosion in acids, alkalis, and sulfides. Galvanized coatings generally undergo passivation treatment. After passivation in chromic acid or chromate solution, the formed passivation film is not easily affected by humid air, greatly enhancing its anti-corrosion ability. For spring parts, thin-walled parts (wall thickness<0.5m), and steel parts that require high mechanical strength, hydrogen removal must be carried out, while copper and copper alloy parts may not require hydrogen removal. Zinc plating has low cost, convenient processing, and good results. The standard potential of zinc is relatively negative, so zinc plating is an anodic coating on many metals. Application: Galvanizing is widely used in atmospheric conditions and other favorable environments. But it should not be used as a friction part
2.Cadmium plating
Characteristics: For parts that come into contact with marine atmosphere or seawater, and in hot water above 70 ℃, cadmium plating is relatively stable, has strong corrosion resistance, good lubrication, and dissolves slowly in dilute hydrochloric acid. However, it is highly soluble in nitric acid, insoluble in alkali, and its oxides are also insoluble in water. Cadmium coating is softer than zinc coating, with less hydrogen brittleness and strong adhesion. Moreover, under certain electrolysis conditions, the obtained cadmium coating is more beautiful than zinc coating. But the gas produced by cadmium during melting is toxic, and soluble cadmium salts are also toxic. Under general conditions, cadmium is a cathodic coating on steel, and an anodic coating in marine and high-temperature atmospheres. Application: It is mainly used to protect parts from atmospheric corrosion caused by seawater or similar salt solutions and saturated seawater vapor. Many parts in aviation, navigation, and electronic industries, springs, and threaded parts are plated with cadmium. It can be polished, phosphated, and used as a paint substrate, but cannot be used as a tableware.
Characteristics: Chromium is very stable in humid atmospheres, alkaline, nitric acid, sulfide, carbonate solutions, and organic acids, and is easily soluble in hydrochloric acid and hot concentrated sulfuric acid. Under the action of direct current, if the chromium layer is used as an anode, it is easily soluble in caustic soda solution. The chromium layer has strong adhesion, high hardness, 800-1000V, good wear resistance, strong light reflection, and high heat resistance. It does not change color below 480 ℃, begins to oxidize above 500 ℃, and significantly decreases hardness at 700 ℃. Its disadvantage is that chromium is hard, brittle, and prone to detachment, which is more pronounced when subjected to alternating impact loads. And it has porosity. Metal chromium is easily passivated in air to form a passivation film, thus changing the potential of chromium. Therefore, chromium becomes a cathodic coating on iron. Application: Directly plating chromium on the surface of steel parts as an anti-corrosion layer is not ideal, and it is generally achieved through multi-layer electroplating (i.e. copper plating → nickel → chromium) to achieve the purpose of rust prevention and decoration. Currently, it is widely used in improving the wear resistance of parts, repairing dimensions, light reflection, and decorative lighting.
nickel plating
Characteristics: Nickel has good chemical stability in the atmosphere and alkaline solution, is not easily discolored, and is only oxidized at temperatures above 600 ° C. It dissolves slowly in sulfuric acid and hydrochloric acid, but is easily soluble in dilute nitric acid. It is easy to passivate in concentrated nitric acid and therefore has good corrosion resistance. Nickel coating has high hardness and is easy to use.
New Gapower Metal Company specializes in providing chrome plated, galvanized, nickel plated steel pipes and round steels. The company has a stock of 20000 tons of round steel pipes. We can provide various specifications of steel pipes, round bars, polished steel pipes, and polished shafts, including American, German, Japanese, and European standards. Welcome to inquire.
Post time: Oct-17-2023