Anodizing is a surface treatment that converts the outer layer of metal into an oxide layer. It is a process that requires electricity to create the oxide layer. The process can be done on most metals, but aluminum is the most common type of metal used in anodizing.
There are three main types of anodizing: decorative (I), hard and protective(II & III). Decorative anodizing changes the color of aluminum and offer poor protection for the material. Hard anodizing offers more protection than decorative. Protective anodizing creates a clear coating over aluminum to protect it from corrosion and wear and tear.
What are the different types of anodizing?
Because the thickness of the oxide film is the most important feature of anodization, the types of anodization are divided into 5 levels according to the minimum average thickness of the oxide film：
| TYPE | Minimum average film thickness(μm） | Minimum film thickness(μm） | ||||||
| AA5 | 5 | 4 | ||||||
| AA10 | 10 | 8 | ||||||
| AA15 | 15 | 12 | ||||||
| AA20 | 20 | 16 | ||||||
| AA25 | 25 | 20 | ||||||
Aluminum anodized to MIL-8625F standard
TYPE I — chromic acid anodizing, conventional oxide film formed in chromic acid tank
TYPE IB—chromic acid anodizing, low voltage process, 22±2V
TYPE IC — non-chromic acid anodizing, application of non-chromic acid formula to form I and IB oxide film
TYPE II — sulfuric acid anodic oxidation, conventional oxide film formed in sulfuric acid tank
TYPE IIB — sulfuric acid anodic oxidation film, the application of non-chromic acid formulations to form I and IB oxide film
TYPE III — hard anodized film
