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Al is amphoteric metal, which is chemically active and easy to generate oxide in air, while aluminum oxide can inhibit further oxidation, the higher purity of aluminum, the more uniform film, and more excellent corrosion resistance. Easy to act with reducing agent. But anti-corrosion to oxidizing agent. Aluminum is passive state to concentrated nitric acid.
Aluminum in the ambient atmosphere will produce a layer of oxide film. Aluminum substrate attached to anode current to generate hard and transparent surface layer in electrolyte, this electro chemical reaction is called as “anodizing”, which is finished by anodizing machine.
Transparent, close to the glass; Insulation, anti-static; Changeable color appearance; Fully integrated with the aluminum surface and does not peel off. NOTE: Passivation is made for stainless steel surface treatment, as the same purpose to increase the corrosion resistance.
Increase corrosion resistance; Increase abrasion resistance; Improve the adhesion of the substrate and coating; Provide an insulating surface; Insulation; Protection polishing surface and machined surface; Improve appearance. Note: After the oxidation can be painted, but generally do not suggest to do this process, because it is uneconomical. Usually to realize color when oxidation, basically except white, other colors are available by this deal, and it will not affect the film thickness (or the thickness of the substrate). These are functions of anodizing machine.
In briefly, anodizing machine divided into 2 big steps: Pre-treatment and After treatment.
Pre-treatment: Include degreasing, etching, chemical polishing, etc.
Oxidation: once the surface is prepared, the oxidation film is built.
After treatment: porous anodizing film can be colored in this stage.
