Type III Anodizing

Type III Engineered Hardcoat

Type III anodizing is done under tightly controlled conditions where the temperature of the sulphuric anodizing solution is held near 32 F or 0 C with very high amperage/current applied to the product. The result is a very durable and hard anodic coating.

Coating thickness can be controlled and is typically specified in the 2 thou range (.002 inches). Coating hardness is typically in the range of 60-70 on Rockwell C-Scale.

Type III anodizing results in a natural colour change to the aluminum and will vary from light tan to black. It is dependent on a number of factors including the temperature, current, duration of anodizing, alloy, and thickness. Color overtones listed below may vary with the use of additives and/or the process. See the following chart for an approximate guide line to what type of natural colour change each alloy typically undergoes during Type III anodizing:

Alloy Series Color Overtones
1000 Grey/Green
2000 Bronze (not recommended)
3000 Grey
4000 Grey
5000 Grey/Brown
6000 Dark Grey/Green
7000 Bronze
Castings Grey (not recommended)

Type III Anodizing Tip

Do not be fooled by anodizers who claim they can produce Type III like anodizing in their Type II tanks. Yes, the coating thickness will be similar but the properties of the coating will not. Type III anodizing takes special equipment and know how. When you specify Type III engineered hardcoat to Altech we provide it to you using our dedicated Type III tank. See the following example of what Type III Engineered Hardcoat should look like.

Example of Engineer Hardcoat

Best results with Type III are achieved with 5000, 6000 and 7000 series alloys. High copper alloys like the 2000 series are not desirable. Neither are castings.


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