Have you ever worked with steel tools or aluminum parts and noticed a golden surface finish on them? Well, that’s alodine coating, and today I will share with you the entire process of alodine finish. But before that, let’s look at what alodine coating is.
What is Alodine Coating?
Adoline finish
Alodine or alodine coating is a surface treatment method that protects the metal surface from corrosion.
Alodine finishing is a chromate conversion coating that applies a conversion coating layer to the aluminum surface, and this passivation processing permits the surface to be corrosion-resistant and improves adhesion properties when painting over aluminum.
Alodine is also called chem film; this chemical process does not alter the mechanical properties of aluminum, like its strength and lightweight.
Chromate conversion coating might be difficult to understand if you’re newly working with aluminum or looking for ways to improve precision machined parts, so I’ll quickly explain chemical conversion coatings.
Coating Chromate Conversion
Chromate conversion coating process is a chemical coating process used on bare metals that need protection from corrosion.
Chromate conversion usually involves dipping aluminum parts into a solution containing hexavalent chromium.
Once in the chromate solution, a chemical reaction occurs between the trivalent chromium and hydroxide ions which deposits a layer of chromium oxide on the surface after the water has evaporated. The chem film or yellow chromate coating is not over a few hundred nanometers thick. It provides excellent corrosion resistance and electrical conductivity and aids the primer for painting on the metal substrate.
In addition to this, it is also used as a decorative finish. Alodine coating has many variables during the chemical conversion coating. Adding other chemicals to the solution can affect the surface finish. Here are two common types of alodine coatings.