Why do aluminum alloys need surface oxidation treatment?

The surface oxidation of aluminum and aluminum alloys is the most important surface treatment process in the processing of aluminum products.

Although aluminum and aluminum alloys naturally form a layer of oxide film in the atmosphere, the film is thin (40-50A) and loose and porous, which is an amorphous, non-uniform and non-continuous film layer, and cannot be used as a reliable protective decorative film layer.

With the continuous development of aluminum processing industry, anodic oxidation or chemical oxidation methods are more and more widely used in industry to generate an oxide film on the surface of aluminum and aluminum alloy parts to achieve the purpose of protection and decoration.

The thickness of the oxide film obtained by chemical oxidation is generally 0.3 ~ 4um, and the soft quality, wear resistance and corrosion resistance are lower than that of the anodic oxide film. Therefore, it is rarely used alone except for special purposes. However, it has better adsorption capacity, and repainting on its surface can effectively improve the corrosion resistance and decoration of aluminum products. The thickness of the oxide film obtained by anodic oxidation is generally 5-20v m, and the thickness of the hard anodic oxide film can reach 60-2500m. The film layer also has similar characteristics:

(1) Aluminum processing has a high corrosion resistance. This is due to the high chemical stability of the anodic oxide film. The test shows that the anodized film of pure aluminum has better corrosion resistance than that of aluminum alloy. This is because the alloy component inclusion or formation of metal compounds can not be oxidized or dissolved, so that the oxide film is discontinuous or void, so that the corrosion resistance of the oxide film is greatly reduced. Therefore, the film obtained after anodizing must be closed in order to improve its corrosion resistance.

(2) Aluminum processing has a strong adsorption capacity. The anodized film of aluminum and aluminum alloy has a porous structure and strong adsorption capacity, so filling the hole with various pigments, lubricants, resins, etc., can further improve the protection, insulation, wear resistance and decorative properties of aluminum products.

(3) Aluminum processing has good insulation properties. The anodized film of aluminum and aluminum alloys does not have the conductive properties of metals, and becomes a good insulating material.

(4) The hardness of aluminum processing is higher. The hardness of pure aluminum oxide film is higher than that of aluminum oxide film. Usually, its hardness is related to the alloy composition of aluminum and the process conditions of the electrolyte during anodizing. The anodic oxide film not only has higher hardness, but also has better wear resistance. In particular, the porous oxide film of the surface layer has the ability to absorb lubricant, and can further improve the wear resistance of the surface.