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Processing technology of oxide film for hard oxidation of aluminum

August 17, 2023
In the surface treatment methods of aluminum and aluminum alloys, aluminum hard oxidation is a method commonly used in industry. The commonly used methods include oxalic acid hard oxidation, phosphoric acid hard oxidation, sulfuric acid hard oxidation and chromic acid hard oxidation. Aluminum hard oxidation process is based on the principle of metal oxidation, through electrolytic oxidation to produce color hard oxide film.
This film not only has good wear resistance. In addition, it also has strong corrosion resistance and the ability to absorb coatings and pigments, and can be used as a primer on the surface of parts.
Aluminum ion concentration: When the aluminum ion content is in the range of 1-12gL, the hard oxidation rate of aluminum and the film layer can play a good coloring effect; If more than 20gL, aluminum ions will be hydrolyzed, the conductivity of the solution will be reduced, colloidal aluminum ions will be adsorbed on the surface of the film, resulting in white spots on the surface of the aluminum profile shell, and the adsorption capacity of the oxide film will also be reduced, resulting in poor coloring. Therefore, the concentration of aluminum ions should be controlled at 3-20gL
In the temperature range of the tank: if the temperature of the tank is too high, the temperature rise of the electrolyte is fast, the dissolution rate of the film is also accelerated, and the corrosion resistance of the oxide film is poor; When the bath temperature is 18-20℃, the oxide film has good adsorption energy, corrosion resistance and elasticity, but the wear resistance is not particularly good; When the temperature of the plating solution is controlled at about 20 degrees, the resulting aluminum oxide film is easy to color.
The quality and anti-corrosion properties of aluminum alloy chromic acid hard oxide film mainly depend on the aluminum alloy composition, film thickness, hard oxidation treatment conditions, such as temperature, current density, water quality and the filling and sealing process after hard oxidation. Therefore, in order to avoid the failure of the hard oxide film similar to that in this paper, we must check the appearance of the hard oxide film of aluminum and eliminate the residual acid generated after the hard oxidation process of aluminum alloy to prevent the anodic oxide film from being corroded and damaged.
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