Chromic Anodizing

Chromic Acid Anodizing as per MIL-A-8625 Type – I

Chromic acid anodizing or type I anodize results in the thinnest anodic coat of the principal three types; typically on the order of .00002”-.0001” (20 to 100 micro inches) per surface. While thin, when properly sealed chromic anodize affords the aluminium equal corrosion protection to the thicker sulphuric and hard coat type anodize.

How is Chromic Acid Anodizing different from other types of anodizing?

Chromic anodize appears much grayer in colour and being thinner absorbs less colour when dyed. This limits chromic acid anodize as a decorative finish, however, it can be dyed black for use as a non-reflective, protective coating on housings for optical components. Even black dyed chromic anodize is lighter in appearance (grayer), than conventional sulphuric black anodize. In order to get chromic anodize to accept black dye, the temperature of the chromic acid must be raised, therefore, it isn’t done every day and must be scheduled accordingly.

What are the attributes / characteristics of Chromic Acid Anodizing?

  • Good for tight tolerance parts: will not change dimensions
  • Can be black dyed – other colours not practical
  • Good for Bonding
  • Non-Conductive
  • Good for welded parts and assemblies

What are some applications of Chromic Acid Anodizing?

  • Precision Machined Components
  • Aerospace Components
  • Welded components and assemblies
  • As a paint/prime base