Alodine / Chemical Conversion

Alodine, so called chromatic passivation or chemical film for aluminum is a chemical conversion process under the MIL-DTL-5541 specification. These coating processes are categorized by the following types, classes and colors.


Types Description   RoHS Compliance  
Type I

 Compositions containing hexavalent chromium.

 Color: Clear or Yellow


Type II

 Compositions containing no hexavalent chromium.

 Color: Clear or Yellow




Classes Description
  Class 1A  

 For maximum protection against corrosion, painted or unpainted.

Class 3

 For protection against corrosion where low electrical resistance is required.



The most common acids used for aluminum anodizing are sulfuric or chromic. U.S. Mil-A-8625 is also the most commonly referenced specification, and describes 3 general types of anodizing:


Types  Classes Thickness (um)
Type I

 Chromic Acid Anodizing

0.5 - 7.6

Type II

 Conventional Sulfuric Acid Anodizing  

 Class 1: A non-dyed anodizing process.

 Class 2: A dyed anodizing process in which you can obtain a large variety of colors.

5.0 - 12.7

5.0 - 25.4

Type III

 Hard Coat Anodizing

 Class 1: A non-dyed anodizing process.

 Class 2: A dyed anodizing process in which black is used.

25.4 - 115.0


Zinc Plating

Zinc plating is the process of covering substrate metals (like carbon steel and alloy steel, etc.) with a layer of zinc to protect the substrate from corrosion. It is usually used to protect and improve the appearance of ferrous metals, as a corrosion barrier. Our Zinc Plating is basically according to ASTM B-633 ELECTRODEPOSITED COATINGS OF ZINC ON IRON AND STEEL.



 Demand        Service Condition      Minimal thickness in microns          

 Fe/Zn25         SC4 (very severe)       25 micron (0.0010")           


 Fe/Zn12  SC3 (severe)  12 micron (0.0005")


 Fe/Zn8  SC2 (moderate)      8 micron (0.0003")


 Fe/Zn5  SC1 (mild)  5 micron (0.0002")





Types Description Corrosion Resistance
according to ASTM B117 
Type I  Zinc coating with no additional treatment N/A  Usually not applicable
Type II  Zinc coating with colorful chromate passivation 96 hours
48 hours
160 hours
 Olive Green
Type III  Zinc coating with colorless chromate passivation 12 hours  Colorless to blue
Type IV  Zinc coating with phosphate passivation N/A  N/A in green coat
Type V  Zinc coating with colorless RoHS compliance passivation  72 hours  Colorless to blue
Type VI  Zinc coating with colorful RoHS compliance passivation 120 hours  Yellow-iridescent