The surface of aluminum profile manufacturer oxide film is composed of porous layer, which is larger than surface area and has high chemical activity. With this characteristic, various coloring treatments can be carried out on the surface of anodic oxide film to improve the decorative and corrosion resistance of the products. However, how can we solve the problem of color changing in anodic oxidation?
1. Pretreatment
Pretreatment includes oil, alkali wash, polishing, etc., whose purpose is to make the aluminum profile surface smooth and glossy feel, and remove  impurities and make it easier to oxidize and stain. In addition, oil removing is to remove grease from the surface of the metal shell by using the oil removing, separation, emulsification and saponification. 
The alkaline wash is to remove excess oil from the saponification of NaOH and remove the natural oxidation film, burr and impurities of the aluminum profile. Acid wash is to stain on the surface after alkali erosion in order to obtain a cleaner surface.
There are two kinds of polishing, one is electrolytic polishing while the another is chemical polishing. Electrolytic polishing is the electrochemical reaction in the aluminum alloy under the effect of electricity and uneven parts of different level appear on aluminum alloy surface, making the aluminum surface smooth. Chemical polishing is the chemical ion reaction that occurs through aluminum and chemical polishing fluid, and the selective dissolution of the rough surface of the sample surface is used to eliminate the abrasion and erosion.
2. Anodic oxidation
Anodic oxidation is the process of oxidation of an oxide film on the anode under the action of an external current.
3. Post-processing
After anodization the film hole of oxide film residue has sulfuric acid solution, so aluminium product must be cleaned by water thoroughly. 
Colouring is the chemical impregnation method which is generally considered to be a combination of both physical adsorption and organic dye functional groups and alumina.
Sealing hole treatment is an indispensable part of anodic oxidation. After oxidation dyeing, only seal processing can ensure the original color of the dye film. Sealing process is of many kinds like steam seal hole, hot water sealing hole, medium temperature sealing hole is good choice, some dye can also choose cold seal technology. The aluminum alloy surface of the oxide film is porous, the adsorption of these pore in the dye adsorbed water of crystallization, thus  the strength of the porous membrane performance can be improved.


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