Anodizing is a chemical process in which electrolytic oxidation is used to create an oxide coating. The process provides a hard outer layer which makes the aluminum part more resistant to corrosion and scratching, etc. The anodizing process produces a hard layer of aluminum hydrate. This compound is porous and it can also be dyed with different colors to make the component look more attractive. The thickness layer is about 0.0005 to 0.002 inches. Automobile parts and electrical housings are some of the common types of components that are anodized. The hard outer layer also acts as a resistor to electricity. You have to be careful when anodizing aluminum as the part will be thicker when it is finished and may not fit its original purpose.
There are three common ways of anodizing aluminum and they will give you different thicknesses of the anodized layer along with other distinct characteristics. Anodizing can also be done with other metals such as magnesium, titanium, and tantalum.
Chromic anodizing is generally used in aerospace and military projects. The anodized coating in this method is very thin, which makes it perfect for complex parts that must fit within very close tolerances. Sulfuric acid is used to etch the surface of the aluminum in sulfuric anodizing. This makes it good for tinting and applying adhesives, and paint or primer coatings. This type of aluminum anodizing is the most common method used. The third type of anodizing is called hardcoating and this method also uses sulfuric acid, but a higher concentration of it is used at a lower temperature.
The aluminum anodizing process uses an acid bath of sulphuric acid, sodium sulphate and sodium hydroxide which is mixed in specific ratios in clean, distilled water. The components that are to be anodized must be thoroughly cleaned and etched to remove all residues of grease and dust.
A battery or an electric current is used as a power input. The component is immersed in the acid bath and is connected to the positive terminal and an electric current is passed through the bath. After being immersed for a fixed amount of time, the component is washed and is ready to use. The acid in the bath is corrosive and you have to be careful not to get any of the solution on your body when you are mixing and handling it.