Definition - What does Conversion Coating mean?
Conversion coating is a type of coating used on metals in which the surface that is covered is turned into a coating with electrochemical or chemical processes.
In addition to corrosion protection, conversion coating also offers enhanced surface hardness. It also can be used as a decorative primer. Some of the best examples of this coating type include phosphate and chromate coatings as well as black oxide. It is normally applied on alloys like aluminum through chromate conversion or anodizing.
Corrosionpedia explains Conversion Coating
Conversion coatings give metals a protective layer made possible through the chemical action between the coating solution and metal. It consists of a thin barrier coating made from aluminum oxide as well as other compounds. Despite the fact that there are many forms of conversion coating, the most typical ones are those made with chromate fluoride.
In general, there are three types of conversion coating:
- Oxide coating: This type of coating is an anti-corrosion product that is ultra thin and offers good adhesion. In such cases, oxide treatments can be performed through electrochemical, heat or chemical reactions. The best examples of oxide coatings include chemical baths, black oxide as well as anodizing.
- Phosphate coating: This is produced by the chemical conversion that exists on a metal substrate in order to produce a highly adhesive phosphate coating. The crystals that may build up on the surface include manganese, zinc and iron. Out of these three, phosphate of manganese is the best type of coating for wear applications. It is ideal for low alloy metals, cast iron and carbon steel. It is one of the most beneficial forms of coating material that is non-metallic.
- Chromate coating: This is comparable to phosphate coating since it is created by chemical conversion. It is formed through the interaction of chromium salts or chromium acid with water solutions. This type of coating is applicable to zinc, aluminum, magnesium and cadmium. This coating typically provides superior corrosive resistance and is broadly used in giving protection to usual household products such as hinges, screws and other hardware items.
The Corrosion Properties of Aluminum and Its Alloys