Sulfuric acid is the most commonly used anodized coating. Coatings of moderate thickness 1.8 um to 25 um (0.00007” to 0.001”) are known as Type II, as name by MIL-A-8625. Coatings thicker than 25 um (0.001”) are known as Type III, hardcoat. Type III is produced in a refrigerated tank near the freezing point of water with higher voltages. Hard Anodizing can be made between 25 and 150 um (0.001” to 0.006”) thick.

Anodizing thickness increases wear resistance, corrosion resistance, ability to retain lubricants, and provides better adhesion for paint primers and glues than bare metal.

Standards for sulfuric anodizing are MIL-A-8625 Types II and IIB, AMS 2471 (undyed), and AMS 2472 (dyed). Standards for MIL-A-8625 Type III are AMS 2469, BS 5599, BS EN 2536 and the obsolete AMS 2468 and DEF STAN 03-26/1.

Anodizing Benefits

- Durability
- Allows coloring
- Ease of maintenance
- Aesthetics
- Nonconductive
- Corrosion resistance
- Increases surface hardness