What is Chromate Conversion Coating?
Chromate conversion coating is also known as chem film, Alodine, or Iridite. It is a type of conversion coating that passivates and converts surface properties of metal parts.
Applications of Chromate Conversion Coating
Chromate conversion coating application is to passivate and protect aluminum, zinc-plated steel, copper, cadmium, silver, magnesium, and tin alloys by minimizing surface oxidation. Some of its applications include:
- Used as a primary coat for paint or powder coat.
- Excellent corrosion resistance. It can withstand 336 hours of salt spray test.
- Conductive in nature.
- Decorative finish.
Types of Chromate Conversion Coating
They are available as hexavalent chromium and trivalent chromium. Trivalent chromium is an environment-friendly RoHS compliant alternative to hexavalent chromium plating.
MIL-C-5541E Specifications
Type I (Hexavalent Chromium)
- Class-1A (Yellow): Offer the maximum corrosion protection and highest electrical resistance.
- Class-3 (Clear or Yellow): Offer the 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.
ASTM-B449-93 Specifications
Hexavalent chromium plating produces byproducts (lead and barium sulfate) that are hazardous and have an impact on the environment. Most industrial standards have banned these substances and replaced them with an environmentally friendly trivalent coating.
To sum up, Chromate conversion coatings are used to passivate zinc, aluminum, copper, silver, magnesium, and tin alloys. We suggest you read this article on what is anodizing.
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