What Is Anodizing?

The anodizing process can only be performed on aluminum and its various alloys.

Anodizing is NOT an applied coating; there is an actual penetration of the aluminum and a build up on the surface of an oxide layer.

Aluminum naturally forms a very thin layer of oxide; the anodizing process provides a much thicker and controlled coating. The anodizing process consists of giving aluminum parts an electrical charge while submerged in an electrolyte bath.

At the beginning of the charge the formation of the oxide film begins to form on the surface. Anodic coating penetrates and grows equally on the aluminum part. This is one of the main reasons for the durability of anodizing.

Commonly used units for anodizing coating thickness

0.001″ = 1.0 mil = 25.4 µ

For a class I part dyed black .7 mil is required to produce a true black.
Lighter colors will require less coating thickness.

The anodic coating can be dyed for cosmetic purposes, as well as for the purpose of color coding of parts. The dye is absorbed into the pores of the anodic coating. The parts can be sealed or left unsealed for further processing, ie., painting, Teflon application, e-coating. Also available is a hot water seal, used for sealing clear parts on customer request.

Alloy A380 (ANSI/AA A380.0) is by far the most widely cast of the aluminum die casting alloys, offering the best combination of material properties and ease of production. It is a high-silicon alloy (about 8 percent). The solubility of silicon in aluminum is about 1.5 percent. When the casting cools, silicon precipitates out and forms gray mottled areas.

Liberty Anodizing offers five dye baths, all with high rating of lightfastness.

Black Blue Gold Purple Red

(Natural or clear is not dyed)

Aluminum Alloy Reference For Anodizing

Series (AA)* Alloying Constituents Metal Properties Properties
1XXX None soft
10 – 27 ksi
2XXX Copper very strong
low elongation
27 – 62 ksi
3XXX Manganese strong
small grain
16 – 41 ksi
4XXX Silicon strong
25 – 55 ksi
5XXX Magnesium strong
18 – 51 ksi
6XXX Magnesium and Silicon strong
18 – 58 ksi
7XXX Zinc very strong 32 – 88 ksi

*AA – Aluminum Association