The anodizing treatment is divided into four basic steps, which are pretreatment, anodic oxidation treatment, coloring treatment of cathodic oxidation, and organic coating treatment. The specific process is as follows.
Pretreatment, pretreatment and includes five steps.
- Degreasing treatment: The purpose is to remove the lubricant and other dirt on the surface of the product, in order to ensure that in the alkali washing process, the surface corrosion of the product is uniform, in order to improve the quality of oxidation products. Degreasing treatment is generally used with a concentration of 5-25% sulfuric acid, degreasing temperature of 60-80c.
- Etching treatment: its purpose is to further remove the dirt on the surface of the product, and the product surface thickness of about 25-1000A natural oxide film removed, so that the base metal surface exposed, in order to facilitate the smooth progress of oxidation and coloring, generally using 40-80 degrees NaOH solution.
- Pickling treatment: the purpose is to remove the black corrosion products remaining on the surface of the product after corrosion, in order to obtain a bright metal surface.
- Matting treatment: the purpose is to make aluminum or aluminum products without luster on the surface so that the formation of non-glossy surface after anodic oxidation treatment, the formation of spot corrosion, generally using 20-40c ammonium fluoride solution.
5, polishing treatment: in order to eliminate mechanical damage and corrosion spots on the surface of aluminum products, improve the surface smoothness and gloss depth generally to polishing treatment.
Basic principle: aluminum cathodic oxidation is essentially the electrolysis of water, when water electrolysis occurs O2- ions and anode aluminum reaction to form aluminum oxide (Al2O3) general electrolyte selection of sulfuric acid, chromic acid, phosphoric acid, oxalic acid, in about 0c sulfuric acid to form a hard porous oxide film. Different materials have great influence on the oxide film. For 6000 series Al-Mg-si (6063.6061.6065), not only protective oxide film can be formed, but also dyeing oxide film, and bright oxide film, but for cast aluminum alloy, protective oxide film can be formed, but dyeing oxide film can generally only form a strong color.
The coloring treatment of cathodic oxidation, there are several methods for coloring treatment as follows.
Electrolytic coloring method.
The method is: the aluminum alloy parts after anodic oxidation are put in the electrolyte of metal salt and electrolyzed again, so that the cations of metal salt are deposited in the bottom layer of the oxide film pinhole and colored, and the bronze color and black color can be obtained in practical application, usually by the salt solution of Ni,Co,Sn as electrolyte, often sulfate, AC electrolysis.
The method is: put the anodized aluminum alloy parts into the solution containing dyes, then the oxide film pinhole adsorption dyes and coloring, dyeing method oxide film with sulfuric acid film is the best, where the representative dyes are ferrous ammonium oxalate (dyed golden yellow) cobalt acetate (bronze color) cathodic oxide film dyeing after the need to seal the hole, there are two main methods.
- Nickel salt sealing hole: with good weather resistance.
- Boiling water sealing: The defect is that the dye is easy to overflow when sealing the hole causing uneven tone.
Organic coating treatment
After cathodic oxidation and coloring treatment of aluminum, in order to improve its corrosion resistance and loading corrosion effect, organic coating treatment can be carried out.
Atomize the paint with fine particle size and then blow it to the surface of the object to be coated to make it become attached material, generally make the paint particles charged on the cathode first, and at the same time apply 100KV DC voltage on the object to be coated as cathode, the paint is generally selected from acrylic resin.
In the aqueous solution of acrylic resin, the oxide film is used as the cathode and electrolysis is carried out with 200V DC voltage to make the oxide film coated with an organic coating film