HARD ANODIZING
What is it? Properties Applications
The anodizing process is an electrochemical process of oxidation, where a hard aluminium oxide (alumina) coating grows on the surface of the aluminium component being processed. This coating is not a surface layer like plating. The coating is created by the chemical reduction of the aluminium. Consequently, the bond strength of the coating is as strong as the aluminium and will not peel or blister.
Special processing procedures in a low temperature, weak electrolyte, result in a very compact coating structure with smaller pores than conventional anodizing. Subsequent sealing of these pores on the very hard film can provide high chemical resistance, as well as other excellent properties.
The Hard Anodizing process is suitable for aluminum alloys with limited alloy composition. Our ANEXDUR PROCESS, allows a coating thickness of up to 150 microns in the following aluminum alloys (as maximum):
Al - Mg (6% Mg)
Al - Cu (5% Cu)
Al - Zn (8% Zn)
Al - Si (13% Si)
This surface treatment can be applied to the entire part or partially applied to selected areas using various masking techniques.
The process complies with military standard MIL-A-8625 Type III.
The Hard Anodizing process provides a dense and very compact coating with the following properties:
These properties allow for light weight aluminum to be used an many high technology applications.
The oxide coating penetrates into the original surface 50% and adds to the original surface 50%. This means that close tolerance machining dimensions should be adjusted to compensate for the change in size. The following figures illustrate the effects that Hard Anodize typically have on machined dimensions.
Since the coating is a result of the controlled oxidation of the aluminum material, different dielectric properties result from different alloys having the same coating thickness:
|
Espesor |
5056 (Magnal 50) |
2017 (Cobral 17) |
|
50 microns |
1.300 Volt. |
2.200 Volt. |
|
125 microns |
2.800 Volt. |
2.200 Volt. |
|
These voltage values are shooting tensions. |
||
|
The micro-hardness values of a 50 micron coating on 6082-T6 alloy, are higher than 420 Hv. |
The temper of the aluminum alloy can result in differences in micro-hardness of components with the same coating thickness:
|
Microhardness values of a 50 micra coating on 2017 (Cobral 17) |
|
|
Temple al aire |
260 Hv. |
|
Temple al aceite |
350 Hv. |
The coating colour depends on the aluminium alloy and its thickness, usually bronze and all scale of grey tones. A subsequent dye process can provide a deep black color to most aluminum alloys.
The hard anodizing treatment had extended to a wide range of applications, mainly in those industries: pneumatic, aerospace, hydraulic, motoring, defense...
Main applications:
