What is a chromate conversion coating?
Chromate conversion coating is a process used to protect aluminum and some other metals from corrosion, often called rust. Corrosion occurs from the reaction of metals and oxygen with present humidity or water. Rust is metal oxide, where oxygen atoms chemically react with metal atoms. Oxidation or rust on the left unorror can be destroyed very quickly by metal parts in a high humite climate.
Even until the 21st century, the chemical process of how chrome atoms create a layer on metal surfaces was well understood. It was known that the metal parts submerged in water based on chrome salts based on water and a small amount of acid creates a very thin layer of chromia on the surface. The chromate conversion process can be performed at a room temperatures in a few minutes. First, however, a zinc coating with a chromat layer can be used later. The chromate coating does not slow down iron or steel rust but protects the zinc that protects steel. Chromate coatings differ in color from bright yellow to darkbrown, part of which is caused by the thickness of the coating and to a lesser extent the metal protected. Darker coatings are usually slightly stronger and offer better corrosion protection.
aluminum has become a popular metal for a new plane at the beginning of the 20th century. Pure aluminum is very soft, so mixtures with copper and other metals were used to produce light but thick parts for aircraft. Corrosion quickly became a problem and normal colors did not prevent it. Chrome metals have been found to reduce corrosion to acceptable levels.
The coating of chromate conversion is often called a chemical film, and the coating layer is quite thin, unlike plating color or zinc. One of the advantages of chromate coatings is their ability to self -use small imperfections, friction or scratches. Chromia atoms can move slowly in the coating layer and eventually re -re -scratches or damage. Big cuts orThe blunted areas cannot be useless and require re -treatment.
For coating aluminum or other metals, a few steps are required. The metals must be extremely clean and usually wash and rinse several times with soap, solvents and water. The surface must be prepared for the coating of the chromate of the surface of the surface with a dose of acid. Etching is a process in which the surface of the metal surface is rough by reacting with an acidic solution that chemically attacks the metal surface. Rinsing must be re -after etching and before using the chromate conversion coating.
Chromate conversion coating is also useful if the part needs to be painted; For example, aluminum does not accept color well and painted surfaces degrade very Quick. Aluminum before treatment with a chrome coating creates a surface that works well with colors and enabled commercial airlines to paint aircraft with their company identification. Chromate coatings do not significantly reduce electrical conductivity, which is the ability toT electrical current. This may be an advantage in aircraft or other vehicles that carry electricity over parts of the frame. Colors and other coatings form layers that block the electric flow, which requires the problem to overcome expensive wiring designs.
The main disadvantage of using chrome coatings was the toxicity of chrome. The type called hexavalent chrome is very toxic to humans and animals and remains in the environment for a very long time. The use of a less toxic trivalent chrome began at the end of the 20th century, which had a certain success, but is less effective as a metal protector than a hexavalent. Research also included other coatings with titanium and zirconium, which saw use for industrial applications.