An extremely thin oxide film formed on the surface of aluminum material in the atmosphere makes it have certain anti-corrosion capability. However, because the film layer is loose, porous and uneven, it cannot be used as a reliable protective film, and the film layer is amorphous, which makes aluminum and its gold lose their original luster and cannot be used as a satisfactory decorative film layer.
The oxide film obtained by chemical oxidation of aluminum is as thick as 0.3 – 4P “. It is soft in quality, low in wear resistance and corrosion resistance: anodic oxide film. Therefore, it is rarely used alone except for special purposes.
First of all, the speed of aluminum film formation is different from that of different types of aluminum materials. after electrical chemical conversion treatment, the difference in appearance color is more obvious than that of oxide films obtained by other process formulas. Aluminum has high purity and slow film forming speed. The purity of aluminum is low, but the opposite is true. Therefore, oxidation should be based on different aluminum materials. In order to achieve this, aluminum parts of different models are not allowed to be bound in the same string, so as not to be unable to control their proper oxidation time. Chemical treatment and mechanical treatment, or directly with chemical treatment. For heavily oxidized metal surfaces, if the oxide layer is thick, aluminum cannot be directly cleaned and chemically treated with solvents, but it is best to carry out mechanical treatment first.
Some methods can be used as reference:

1. Degreasing treatment, wiping with absorbent cotton wet solvent, removing oil stain, wiping with clean cotton cloth several times. Common solvents include trichloroethylene, ethyl acetate, acetone, butanone and gasoline.
2. After degreasing, chemical treatment is carried out in the following solution: ammonium hydrogen fluoride 3 – 3.5, chromium oxide 20 – 26, sodium phosphate 2 – 2.5, concentrated sulfuric acid 50 – 60, boric acid 0.4 – 0.6, and water 1000 is soaked at 25 – 40°C for 4.5 – 6 min, namely water washing and drying are carried out.
3. After degreasing, anodizing is carried out in the following solution: 22g / l concentrated sulfuric acid is immersed for 10 – 15 min under the direct current intensity of 1 – 1.5aA/ dm2, then immersed for 5 – 20min under 95 – 100 °C in saturated potassium dichromate solution, and then washed with water and dried. The treated metal surface has high activity and is more easily polluted by dust, moisture, etc. Therefore, the treated metal surface should be bonded as quickly as possible.