All About Anodizing

What is Anodizing ?

Anodizing is an electrolytic process for producing thick oxide coatings on aluminium alloys. It improves surface resistance to wear and corrosion. Anodizing is also used as primary coat for powder coating and as a decorative layer.

Machining, drilling or welding of a component shall be done before anodizing process. 

Non-metallic materials such as Magnesium and Titanium materials can also be anodized.

Anodizing can be classified in following Types :

  1. Type-I Chromic Acid Anodizing
  2. Type-II Sulphuric Acid Anodizing
  3. Type-III Hard Anodizing

Type-I Chromic Acid Anodizing

Anodizing color varies from a very light gray to a dark olive color depending on aluminum alloy. Type-I  anodizing is used in aerospace industry to achieve higher corrosion resistance and as a primary coat for powder coating. Salt spray testing can be done upto 336 hours.

This can be further classified in three categories :

  1. Type-I
  2. Type-IB
  3. Type-IC

Type-II Sulphuric Acid Anodizing

Sulphuric acidic anodizing process involves, immersing the aluminium into sulphuric acid solution and passing current through the aluminium.

Type-II anodizing can further classified in two classes.

  1. Class-1 : Un-dyed anodized finish
  2. Class-2 : Dyed anodized finish (various color options)

Representation of Type-II Finish :

Red Anodized (MIL-A-8625, Type-II, Class 2)

Type-III , Hard Anodizing

Hard anodizing process involves immersing the aluminum into sulphuric acid solution at low temperature and high voltages. As a result hard wear and abrasion resistant layer of aluminum oxides produced.

Hard anodizing can further classified in two classes.

Class-1 : It produces hard clear anodizing layer.

Class-2 : It produces hard Black anodizing layer 

Representation of Type-III Finish :

  • Clear Hard Anodized (MIL-A-8625, Type-III, Class 1)
  • Black Hard Anodized (MIL-A-8625, Type-III, Class 2)
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