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Mil Spec: MIL-DTL-5541F
Types. The chemical conversion coatings are of the following types.
Type I – Compositions containing hexavalent chromium
Type II – Compositions containing no hexavalent chromium
Classes. The materials, which form protective coatings by chemical reaction with aluminum and aluminum alloys, are of the following classes
Class 1A – For maximum protection against corrosion, painted or unpainted.
Class 3 – For protection against corrosion where low electrical resistance is required.
ASTM Designation: B 449
Classification of Chromate Coatings
|Class*||Appearance||Coating Mass per Unit Area, g/m2||Corrosion Protection|
|1||Yellow to brown||0.4 to 2||Maximum corrosion resistance generally used as final finish|
|2||Colorless to yellow||0.1 to 0.4|
Moderate corrosion resistance, used as a paint base and for bonding to rubber.
3 Color less<0.1 Decorative, slight corrosion resistance, low electrical contact resistance.4Light green to green0.2 to 5Moderate corrosion resistance, used as a paint base and for bonding to rubber * No relationship exists between class numbers and degree of corrosion resistance. Class numbers have been assigned on the basis of traditional usage and for compatibility with national standards.