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Alodine (Also called Chromate conversion coating) refers to creating a small protective thin layer on the surface of substrate material using a solution containing chromium ions.
Alodine is a chemical that dissolves in an aqueous solution to create a gel for metals such as aluminum alloys. It forms a coating that protects the metal and enhances its aesthetic appeal. However, the name “Alodine” is registered as a trademark by Henkel Surface Technology. The common name for this chemical film is “chromate conversion coating”.
A chromate conversion coating is a chemical conversion coating. In chemical conversion coatings, metals undergo chemical reactions on the surface. This chemical reaction converts the metal surface into a protective layer.
While providing aluminum corrosion protection, chemical films or Alodine coatings also provide the basis for the surface finish of organic coatings, which prevent loss of electrical conductivity.
The chemical film is applied by dipping, brushing or spraying, and the thickness of the chromate conversion coating does not change the size of the part. A conversion coating on aluminum can also improve paint and primer adhesion if it is applied to the aluminum surface before primer.
| Applicable Materials | Colors | Applications | Thickness |
| Aluminum | Clear, Gold | Tools, hardware, electrical systems | 0.25-1.0 μm0.00001-0.00004 inches |
Alodine anodizing is a kind of aluminum alloy surface treatment, which is mainly used to improve the corrosion resistance of aluminum alloy structure and the adhesion ability of the primer. It is a commodity name for surface treatment of aluminum alloy and can be reached on the surface of aluminum alloy, producing a thin 0.5-4 micron anodizing film. The electrochemical reaction of chromate is the principle of the Alodine anodizing. It is main composed of chromic anhydride, tetrafluoroborate, sodium fluoride, and other substances in a certain proportion.
Due to its low density, high strength and high electrical and thermal conductivity, good plasticity, easy CNC machined, and good corrosion resistance properties,aluminum materials are widely used in various industry fields.
Aluminum alloy is made of pure aluminum by adding some alloying elements.However aluminum alloy has better physical and mechanical properties than pure aluminum. Because aluminum element is a relatively active metal which can spontaneously form an extremely thin oxide film in the air, which makes it have better corrosion resistance, but the thickness for the film is very thin ,it is only about 4nm with low hardness and poor wear resistance. Therefore, it is necessary to manually cover the surface with a film to achieve the purpose of protection. It can usually be achieved through aluminum alodine solution immersion treatment technology.
It is soft &porous and has good adsorption properties. And it will not affect the mechanical properties of the material, not affecting the size of the parts. It usually calls as the bottom layer of paint or other coatings.
Chromate conversion coating, more commonly known as chem film or by its brand name Alodine, is a chemical coating that passivates and protects aluminum from corrosion. It is also used as a base layer before priming and painting parts. The standard most commonly specified in engineering applications is MIL-DTL-5541F, which refers specifically to coating of aluminum alloys.
This protective layer is much thinner than an anodizing layer, and while both are created by immersion of parts into a bath, Alodine is a simple chemical coating and the process does not use electrical current.
Alodine is a slightly cheaper process than anodizing, though it is more prone to scratches, wear, and cosmetic damage. The most common color of the coating is an iridescent greenish-gold, and thus it may also be used for cosmetic purposes. However, this color comes from hexavalent chromium, which is toxic, so for RoHS compliance needs, there are clear versions of the coating available as well.
Alodine is a coating process that improves the part’s corrosion resistance without impacting the final dimensions of the aluminum part. Unlike the anodizing process, which has a similar effect as allodizing, an alodine finish functions as a primer and allows the part to be painted if required. This is due to the passivation process, which applies a coating to the part.
Alodine: according to the chemical reaction of aluminum alodine liquid, the lively aluminum metal surface layer becomes an inert surface layer, thus preventing the reaction between the external destructive substances and the metal surface to achieve the purpose of extending the rusting time of aluminum.
Anodizing: an electrolytic oxidation process in which the aluminum surface is usually transformed into an oxide film, which has protective, decorative, and other functional properties.
We offer our clients complete alodine finishing services, enabling them to capture faster turnarounds on their precision parts and giving them peace of mind that the high tolerance specifications for the final parts are met.
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