Chromate Conversion Coatiing

What is Chromate Conversion Coating ?

Chromate conversion coating is a type of conversion coating. Conversion coatings generally converts surface properties of substrate materials. 

Chomate conversion coating is used to passivate zinc-plated Steel, aluminium, copper, silver, magnesium and tin alloys. They are also known as chem film, alodine or iridite.

Coatings Types

They are available as hexvalent and trivalent chromates. Hexavalent coatings are banned because of their poisonous nature. Trivalent coatings are more popular these days.

Properties of Chromate Conversion Coatings
  • Excellent Corrosion Resistance
  • Conductive in nature
  • Used as primary coat for paint or powder coat.
  • Can withstand 336 hour salt spray test.
  • Chromate conversion coating are amorphous with a gel like composition hydrated with water. This characteristic helps aluminum them in self healing while scratched.

Specifications (MIL-C-5541E)

Type I (Hexavalent Chromium)
  • Class-1A (Yellow) : Maximum corrosion protection and highest electrical resistance.
  • Class-3 (Clear or Yellow) : Lowest corrosion protection and low electrical resistance.
Type II- (Trivalent chromium) 

Class-1A (Clear) : Maximum corrosion protection and highest electrical resistance

Class-3 (Clear) : Lowest corrosion protection and low electrical resistance.

Specifications (ASTM-B449-93)

Class Appearance Corrosion Protection
Class 1 Yellow to Brown Used as Final Finish Operation
Class 2 Colorless to Yellow Moderate Corrosion Resistance, generally used as paint base
Class 3 Colorless Low corrosion and electrical resistance, Used as decorative finish
Class 4 Light green to green Moderate corrosion resistance

Conclusion

To sum up, Chromate conversion coatings is a type of conversion coatings. They are used to passivate zinc, aluminum, copper, silver, magnesium and tin alloys.

Got Question?  

We will be happy to help. If you think we missed Something?  You can add to this article by sending message in comment box or Contact Us. We will do our best to add it in this post.

You can also write an article to share your knowledge.

Was the Article Helpful? Help Us by Sharing

Add a Comment

Your email address will not be published. Required fields are marked *