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")

 

ASTM Type

 

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