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.

 

TypesDescription  RoHS Compliance  
Type I

 Compositions containing hexavalent chromium.

 Color: Clear or Yellow

No

Type II

 Compositions containing no hexavalent chromium.

 Color: Clear or Yellow

Yes

 

 

ClassesDescription
  Class 1A  

 For maximum protection against corrosion, painted or unpainted.

Class 3

 For protection against corrosion where low electrical resistance is required.

 

Anodizing

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 ClassesThickness (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.

 

Class

 Demand       Service Condition     Minimal thickness in microns          

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

II 

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

III

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

     IV     

 Fe/Zn5 SC1 (mild) 5 micron (0.0002″)

 

 

<thASTM Type</th

 

TypesDescriptionCorrosion Resistance
according to ASTM B117 
Remarks
Type I Zinc coating with no additional treatmentN/A Usually not applicable
Type II Zinc coating with colorful chromate passivation96 hours
48 hours
160 hours
 Yellow-iridescent
 Black
 Olive Green
Type III Zinc coating with colorless chromate passivation12 hours Colorless to blue
Type IV Zinc coating with phosphate passivationN/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 passivation120 hours Yellow-iridescent
 Black

 

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