Aluminum and aluminum alloys naturally form an oxide film in the atmosphere, but the film is thin (40-50 A) and loose and porous. It is amorphous, uneven and continuous, and cannot be used as a reliable protective decoration. Sex film layer. With the continuous development of the aluminum product processing industry, anodizing or chemical oxidation is widely used in the industry to form an oxide film on the surface of aluminum and aluminum alloy parts to achieve the purpose of protection and decoration. The oxide film obtained by chemical oxidation is generally 0.3 to 4 um in thickness, and the softness, abrasion resistance and corrosion resistance are lower than that of the anodized film. Therefore, it is rarely used alone except for special purposes. However, it has a good adsorption capacity and is repainted on its surface, which can effectively improve the corrosion resistance and decorativeness of aluminum products. The thickness of the oxide film obtained by anodizing is generally 5-20V m, and the thickness of the hard anodized film can reach 60-2500m. Its film also has similar characteristics:
(I) The hardness of aluminum processing is high. The hardness of pure aluminum oxide film is higher than that of aluminum alloy oxide film. Generally, its hardness is related to the alloy composition of aluminum and the process conditions of the electrolyte during anodization. The anodized film not only has higher hardness, but also has better wear resistance. In particular, the oxide film having a porous surface layer has the ability to adsorb a lubricant, and can further improve the wear resistance of the surface.
(2) Aluminum processing has high corrosion resistance. This is due to the high chemical stability of the anodized film. After testing, the anodized film of pure aluminum is better than the anodized film of aluminum alloy. This is because the inclusion of the alloy component or the formation of the metal compound cannot be oxidized or dissolved, and the oxide film is discontinuous or voids are generated, so that the corrosion resistance of the oxide film is greatly lowered. Therefore, the film obtained by anodizing generally must be subjected to a sealing treatment to improve its corrosion resistance.
(3) Aluminum processing has strong adsorption capacity. The anodized film of aluminum and aluminum alloy has a porous structure and has a strong adsorption capacity. Therefore, filling the holes with various pigments, lubricants, resins, etc. can further improve the protection, insulation, wear resistance and decorative properties of the aluminum products.
(4) Aluminum processing has good insulation properties. The anodized film of aluminum and aluminum alloys does not have the conductive properties of metals, and becomes a good insulating material.
(5) Strong heat insulation and heat resistance. This is because the thermal conductivity of the anodized film is much lower than that of pure aluminum. The anodized film can withstand temperatures of about 1501 C, while pure aluminum can only withstand 660 ° C. In summary, aluminum and aluminum alloys are chemically oxidized, especially after anodizing, and the oxide film formed on the surface has good protection and decoration characteristics. Therefore, it is widely used in aviation, electrical, electronics, machinery manufacturing and light industry.
There are many kinds of decorative oxidation processes for aluminum and aluminum alloys, which can be generally divided into chemical oxidation method and electrochemical oxidation method, that is, anodizing method. Among them, the application of anodizing treatment is more extensive. This is because the oxide film obtained by the anodic oxidation method is superior to the oxide film obtained by all chemical oxidation methods.
After chemical or electrochemical polishing of aluminum and aluminum alloy parts, after anodizing, a smooth, bright, high-transparency oxide film layer can be obtained, and then dyed, a variety of colorful and attractive surfaces can be obtained. If it is oxidized under a certain process condition, a glaze layer can be formed on the surface to obtain a special decorative effect on the surface of the aluminum product.
According to incomplete statistics, the decorative oxidation process of aluminum and aluminum alloys in China has grown to dozens of kinds, which makes the development of China's aluminum products processing industry change with each passing day.
First, chemical oxidation
The chemical oxidation treatment of aluminum and aluminum alloy can be divided into two types: alkaline and acidic solution oxidation treatment according to the nature of the solution. According to the nature of the film, it can be divided into oxide film layer, phosphate film layer and chromic acid. Salt film and chromic acid to phosphate film.
(1) Process specifications.
1. Alkaline chemical oxidation process specification.
Anhydrous sodium carbonate (Na2C03) 50g/L
Sodium chromate (Na2Cr04) 15g/L
Sodium hydroxide (NaOH) 25g / L
Temperature 80--100 'c
After oxidation, the parts should be cleaned immediately, passivated in 20g / L chromic acid solution and room temperature for 5 ~ 15 seconds, then cleaned, dry work. The color is golden yellow. The film thickness is 0.5 to 1 um, which is suitable for pure aluminum, aluminum magnesium, aluminum manganese alloy.
2. Phosphate-chromate oxidation process specification
Formulation 1: Phosphoric acid (H3P04) 50--60mL/L
Chromic anhydride (Cr03) 20-25 g/L
Ammonium hydrogen fluoride (NHOHF2) 3～3.5g/L
Boric acid (H3B03) 1～1.2g/L
Time 3 to 6 minutes
This method uses more phosphoric acid, so it is also called phosphating. The color of the oxide film is colorless to light blue, and the film thickness is about 3-49m. The film is dense, the corrosion resistance is high, and the size of the parts after oxidation is unchanged. It is suitable for various aluminum and its alloys. · In order to further improve the corrosion resistance, it can also be filled. After the oxidized cleaning, the parts can be immersed in 40-45g/L potassium dichromate solution at a temperature of 90--98 ° C for 10 minutes, then dried in an oven at <= 70 ° C. Suitable for general parts. It can also be immersed in a boric acid solution of 20-30 g/L at a temperature of 90-98 ° C for 10-15 minutes, and then dried in an oven at 70 ° C by washing. Suitable for aluminum rivets, etc.
Formulation 2: phosphoric acid (H3P04) 45g/L
Chromic acid drunk (Cr03) 6g / L
Sodium fluoride (NaF) 3g / L
Time 10-15 min
The film layer is thin, good toughness, high corrosion resistance, suitable for aluminum and aluminum alloy parts that need to be deformed after oxidation.
Formula 3: Phosphoric acid (H3P04) 22g/L
Chromic acid drunk (Or03) 2.--4g/L
Sodium fluoride (NaF) 5g / L
Qing acid (H3BOO 2g/L
Temperature room temperature
This method is also known as chemically conductive oxidation. The oxide film is colorless and transparent; the film layer is thin, the magical value is 0.3-0.5um, and the electrical conductivity is good, and it is mainly used for easily deformable aluminum electrical parts.
3. Chromate Process Oxidation Process Formulation 1: Chromic anhydride (Cr03) 4N 6g/L
Sodium fluoride (Na-F) lg/L
Potassium ferricyanide [K3Fe(CN)6]0.5g/L
Temperature 30-35 0C
The color of the oxide film is iridescent, the film is thin, and the electrical conductivity is good. It is mainly used for aluminum electrical parts that have certain electrical conductivity.
Formula 2: Chromic acid drunk (Cr03) 3.5 ~ 6g / L
Sodium dichromate (NaZCrZO7) 3～3.5g/L
Sodium fluoride (NaF) 0.8g / L