Chromate/Chem Film

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Chemical Films Mil Spec Thickness Comments
MIL-C-5541E
Coatings for aluminum. Color can vary colorless to golden - iridescent - brown, or can be dyed in specific colors. Materials should conform to MIL-C-81706. Coatings shall be continuous, free from powdery areas, breaks, scratches, etc.   No dimensional change Class 1A is used as a corrosion preventative film (unpainted) or to prove adhesion of paint finish systems.

Class 3 is used as a corrosion preventative film for electrical and electronic applications where low-resistance contacts are required.


ASTM Designation: B 449

Chromates on Aluminum

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
 Colorless
<0.1
 Decorative, slight corrosion resistance, low electrical contact resistance.
4
 Light green to green
0.2 to 5
 Moderate 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.


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