The anodic oxidization of aluminum alloy

1.Definition of anodic oxidization

Anodic oxidization is a kind of electrolytic oxidation. In this process the surface of aluminum alloy generally transfers into a oxidation film, which has protection, decoration and some other functions.

2.Classifications of anode oxide film

There are two types of oxidation films: barrier oxide film and porous oxide film. Barrier oxide film is a compact nonporous and thin oxide film immediately before metal surface. Its thickness depends on applied voltage is no more than 0.1um. Porous oxide film consists of two oxidation films: barrier layer and porous layer. The thickness of barrier layer is related to applied voltage while the thickness of porous layer is determined by the power passed. We use porous layer most commonly.

3.Features of anode oxide film
 

a.The structure of oxide film assumes porous honeycomb. It has good adsorption capacity with the porosity. It can be used as under-coating of piating coacing or be stained to increase the decorative effect.

b.The structure of oxide film has high hardness. Anode oxide film has high hardness with the hardness about 196－490HV. Its has excellent wear resistance because of the high hardness.

c.The corrosion resistance of oxide film. Aluminum oxidized film is stable in the air and soil, having good binding ability with parent material. Generally, stain sealing or spray process is used to further improve its corrosion resistance after oxidation.
  
d.The binding force of oxide film. Oxide film has good binding ability with parent material and it is hard to separate them with mechanical methods. Even if layer bends with the metal, it can still keep a favorable combination of parent material. But it would crack when layer is to be subjected to considerable shock loads and bend and deform because of its small plasticity and heavy brittleness. As a result, this kind of oxide film is not easy to be used in mechanical action but for under-coating of the paint coating.
   

e. The insulation property of oxide film and the impedance of anodic oxide film of aluminum are somehow high while the thermal conductivity is rather low. And the heat endurance can reach 1500 degree and the thermal conductivity is 0.419W/(m•K)—1.26 W/(m•K). It can be used as insulating layer of dielectric or electrical products of electrolytic capacitor.

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