Understanding types and classes of anodizing

Table of Contents

Understanding types and classes of anodizing

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:

TYPEMinimum average film thickness(μmMinimum film thickness(μm
AA554
AA10108
AA151512
AA202016
AA252520

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

Author: Mose Li

Author: Mose Li

Director of Project Engineering at 3Q Machining

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