Galvanized
Features
Zinc is relatively stable in dry air and is not easy to change color. In water and humid atmosphere, it reacts with oxygen or carbon dioxide to form oxide or alkaline zinc carbonate film, which can prevent zinc from continuing to be oxidized and play a protective role.
Zinc is extremely susceptible to corrosion in acids, alkalis, and sulfides. Zinc coatings generally undergo passivation treatment. After passivation in chromic acid or a chromate solution, the resulting passivation film is less susceptible to humid air, significantly enhancing corrosion resistance. Dehydrogenation is essential for spring parts, thin-walled parts (thickness < 0.5 ฮผm), and steel parts requiring high mechanical strength. Dehydrogenation is not required for copper and copper alloy parts.
Galvanizing has low cost, convenient processing and good effect. The standard potential of zinc is relatively negative, so zinc coating is anodic coating for many metals.
Application
In atmospheric conditions and other good environments, galvanizing is widely used. But it is not suitable for friction parts.
Chrome Plating
Features
Chromium is very stable in humid atmosphere, alkali, 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 and high hardness (800-1000V), good wear resistance, strong light reflectivity, and high heat resistance. It does not change color below 480ยฐC, begins to oxidize above 500ยฐC, and its hardness drops significantly at 700ยฐC. However, its disadvantages are that chromium is hard, brittle, and easily detached, especially under alternating impact loads. It is also porous.
Metal chromium is easily passivated in the air to form a passivation film, which changes the potential of chromium. Therefore, chromium becomes a cathodic coating on iron.
Application
Directly plating chrome on steel parts as an anti-corrosion layer is not ideal. Generally, multi-layer electroplating (i.e., copper โ nickel โ chromium) is required to achieve rust prevention and decorative purposes. Currently, it is widely used to improve part wear resistance, repair dimensions, light reflection, and decorative lighting.
Cadmium Plating
Features
For parts in contact with marine atmosphere or seawater and in hot water above 70ยฐC, the cadmium coating is relatively stable, has strong corrosion resistance, and good lubricity. It dissolves very slowly in dilute hydrochloric acid, but dissolves very easily in nitric acid. It is insoluble in alkali, and its oxide is also insoluble in water.
The cadmium coating is softer than the zinc coating, has less hydrogen embrittlement, and has stronger adhesion. Moreover, under certain electrolytic conditions, the obtained cadmium coating is more beautiful than the zinc coating.However, the gases produced by cadmium when melted are toxic, and soluble cadmium salts are also toxic. Due to environmental concerns, cadmium plating is now rare, largely replaced by nickel and chromium plating. Because cadmium is toxic, it is only used in a few military products.
Under normal 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, as well as saturated seawater vapor. Many aviation, marine, and electronic industrial parts, springs, and threaded parts are plated with cadmium. It can be polished, phosphated, and used as a paint base, but it cannot be used as tableware.
Nickel Plating
Features
Nickel has good chemical stability in the atmosphere and alkaline solutions, is not easily discolored, and only oxidizes at temperatures above 600ยฐC. It dissolves very slowly in sulfuric acid and hydrochloric acid, but is readily soluble in dilute nitric acid. It is easily passivated in concentrated nitric acid, resulting in excellent corrosion resistance.
Nickel coating has high hardness, is easy to polish, has high light reflectivity and can increase aesthetics. Its disadvantage is that it is porous. To overcome this disadvantage, multiple metal coatings can be used, with nickel as the middle layer.
Nickel is a cathodic coating on iron and an anodic coating on copper
Application
Usually in order to prevent corrosion and increase the beauty of the product, it is generally used to protect the decorative coating. Nickel plating is ideal for corrosion protection of copper products.
However, since nickel is relatively expensive, copper-tin alloy plating is often used instead of nickel plating.
The Differences Between Zinc Plating, Chrome Plating, Cadmium Plating And Nickel Plating
When purchasing self-tapping screws, many purchasers only have requirements for the surface color of the screw fasteners and the performance of the screws. Many purchasers do not pay attention to the surface treatment of the screws and why these surface treatments are required. Here is a brief introduction for everyone:
Differences:
1. Different appearance colors
1) Galvanized appearance is silvery white.
2) Nickel plating has a silvery-white, yellowish appearance.
3) Chrome plating is divided into decorative chrome and hard chrome, with a bright white and bluish appearance.
2. Different definitions
1) Galvanizing refers to a surface treatment technology that coats a layer of zinc on the surface of metal, alloy or other materials for aesthetic purposes and rust prevention.
2) The method of plating a layer of nickel on metals or certain non-metals by electrolysis or chemical methods is called nickel plating.
3) Chromium is a silvery-white metal with a slight bluish tint. The process of plating a layer of chromium on metals or certain non-metals by electrolysis or chemical methods is called chromium plating.
3. Different characteristics
1) Galvanizing has low cost, general corrosion resistance and is silvery white in color.
2) Nickel plating is beautiful and can be used for decoration, but it is expensive and the process is slightly complicated. The color is silvery white with a yellowish tint.
3) There are two types of chrome plating. The first one is for decoration, with a bright surface and good wear resistance. Its rust prevention ability is not as good as galvanizing, but better than oxidation. The second one is to increase the hardness and wear resistance of metal parts, which is the functionality of the parts.
4. Different uses
1) Galvanizing is used in screws, circuit breakers, industrial supplies, etc.
