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 |
No |
|
Type II |
Compositions containing no hexavalent chromium. Color: Clear or Yellow |
Yes |
| Classes | Description |
| 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 | 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.
|
Class |
Demand | Service Condition | Minimal thickness in microns |
|
I |
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") |
| Types | Description | Corrosion Resistance according to ASTM B117 |
Remarks |
| 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 |
Yellow-iridescent Black 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 Black |
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