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Chromate Treatment

Last updated: August 25, 2017

What Does Chromate Treatment Mean?

Chromate treatment is a chemical process where a chromium compound solution is applied to a metal surface, to form a protective chemical coating of chromate. A chemical reaction occurs between the base material and chromic-acid-bearing compound to produce a corrosion-resistant film that is physically and chemically bonded to the base metal.


Corrosionpedia Explains Chromate Treatment

The chromate treatment process starts with degreasing, washing, etching and rinsing, to clean, roughen up and increase the metal’s surface area. The chromate treatment is then applied by spraying or immersion.

The reaction forms a complex, metal-chrome molecular film, which is a jellylike coating that passivates the metal surface and renders it chemically inactive, electrically neutral and immune to galvanic corrosion. This film offers corrosion protection of the base metal or any other metal plated over the base metal.

Coating appearance varies from yellow to dark brown and is partly determined by metal type and coating thickness. Thicker coatings offer darker colors and better corrosion protection.

Advantages of chromate treatment include:

  • Improved corrosion resistance due to the continuous coating which covers the metal surface and prevent direct contact with corrosive environments
  • Decorative features such as natural appearance, clear, light gold iridescence, golden brown, etc.
  • Provides an effective base for paints
  • Minimal buildup on the surface
  • Good electrical conductivity

Uses of chromate treatment include:

  • Decorative purposes
  • Paint primers
  • Protecting products such as hinges, screws and hardware items
  • Aluminum parts in the aircraft and other industries
  • Corrosion protection of:
    • Aluminum
    • Copper
    • Cadmium
    • Magnesium
    • Silver
    • Tin
    • Zinc
    • Alloys of these metals

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