The introduction of anodizing aluminum surface treatment technology effectively solves the defects of aluminum materials, broadens the application field of aluminum materials, and becomes a new hot spot in construction, renovation, and decoration applications.
1. What is Anodizing Aluminum?
Anodizing aluminum is an electrolytic oxidation process, and it is a surface treatment method for industrial aluminum profiles. This treatment method is to form an oxide film on the surface of industrial aluminum profiles. functional characteristics. The anodization of aluminum from this definition only includes the part of the process of forming an anodized film.
Under the corresponding electrolyte and specific process conditions, aluminum and its alloys form an oxide film on the aluminum product (anode) due to the action of the applied current. In order to overcome the defects of aluminum alloy surface hardness, wear-resistance, and other aspects, expand the scope of application, and prolong the service life, surface treatment technology has become an indispensable part of the use of aluminum alloy, and anodic oxidation technology is a widely used technology.
2. What is Anodic Oxidation？
The principle of anodization: The metal or alloy is regarded as an anode, and an oxide film is formed on the surface by electrolysis. Metal oxide films change the state and properties of metal surfaces, such as surface coloration, and increase corrosion resistance, wear resistance, and hardness of metal parts.
Of all the metals suitable for anodization, aluminum is the most widely used.
Aluminum and its alloys are put into the electrolyte as an anode, and electrolysis is carried out under specific conditions. After the aluminum of the anode is oxidized, a thin layer of aluminum oxide will be formed on the surface, and its thickness is about 5-30 microns. The thickness of hard anodic oxide film will be greatly increased to 25-150 microns. The purpose of Anodizing aluminum is to increase the performance of the part, thereby improving the safety of the application area.
For example, the hardness and wear resistance of anodized aluminum have been improved, reaching 250-500 kg/mm2, and its good heat resistance also makes its melting point as high as 232°. In addition, the Anodizing aluminum metal will have excellent insulation, and experiments have proved that the breakdown voltage of anodized aluminum is as high as 2000V or more.
3. What are the Characteristics of Aluminum Anodizing?
- The Corrosion Resistance. The aluminum anodic oxide film can effectively protect the aluminum substrate from corrosion. The performance of the anodic oxide film is obviously better than that of the naturally formed oxide film. The film thickness and sealing quality directly affect its corrosion resistance.
- Hardness and Wear Resistance. The hardness of aluminum anodization is much higher than that of the aluminum substrate, the hardness of the substrate is HV100, the hardness of the ordinary anodized film is about HV300, and the hard oxide film can reach HV500 or more. The relationship between wear resistance and hardness is consistent.
- Decorative. The aluminum anodized film protects the metallic luster of the polished surface, and the anodized film can also be stained and tinted to obtain and maintain a colorful appearance.
- Organic Coating and Electroplating Adhesion. The aluminum anodized film is a method for the aluminum surface to receive organic coatings and electroplating layers, which can effectively improve the adhesion and corrosion resistance of the surface layer.
- Electrical Insulation. Aluminum is a good conductor, and aluminum anodized film is a high-resistance insulating film. The dielectric breakdown voltage is greater than 30V/um, and the specially prepared high insulating film even reaches about 200V/um. Transparency. The transparency of the aluminum anodized film itself is very high, and the higher the purity of aluminum, the higher the transparency. Both the purity and alloy composition of the aluminum alloy material has an effect on transparency.
- Properties. Various functional materials can be obtained by depositing functional particles in micropores by utilizing the diversity of anodic oxide films. Functional components under development can have electromagnetic functions, catalytic functions, sensing functions, and separation functions.
4. Coloring Process of Anodized Aluminum
The coloring process of anodized aluminum can not only give the parts good hardness and corrosion resistance but also make the parts more aesthetic. At present, the aluminum anodizing coloring process can be divided into three categories: chemical dyeing, electrolytic coloring, and electrolytic overall coloring.
Anodized Aluminum Chemical Coloring: Chemical coloring is a very widely used anodized coloring process. Chemical dyeing is to use the characteristics of the pores of the oxide film layer to realize the coloring of the oxide film by chemically active adsorption. According to the coloring mechanism and process, it can be divided into organic dye coloring, inorganic dye coloring and color paste coloring, and so on.
Anodized Aluminum Electrolytic coloring: Electrolytic coloring is also a process technology that often occurs in anodizing dyeing. First of all, compared with chemical coloring, electrolytic coloring is to realize electric current electrolysis by placing the anodized aluminum metal in an aqueous solution containing metal salts.
Anodized Aluminum Electrolytic coloring is easier to operate than chemical coloring costs will be reduced accordingly. For Anodized Aluminum electrolytic coloring, it should be noted that when metals, metal oxides, and metal compounds are deposited at the bottom of the porous layer of the oxide film, various colors will appear due to the scattering effect of the electrodeposits on the light. Do not over-color.
Anodized Aluminum Electrolytic overall coloring: The Anodized Aluminum electrolytic overall coloring process can save processing time because, at the same time as the anodizing, the coloring is also carried out accordingly. Anodized Aluminum Electrolytic overall coloring film has good light resistance, heat resistance, and corrosion resistance. In recent years, professionals have found through practical application tests that the aluminum metal after electrolytic overall coloring also has very strong wear resistance.
5. Common Electrolytes Used in Anodizing
The anodizing process is to add a protective film to the metal surface by aluminum anodizing to increase hardness, corrosion resistance, and wear resistance. The metal itself will not be oxidized as an anode, so how the anode is formed depends on the electrolyte in which the metal is placed. At present, there are many electrolytes commonly used in industrial production, and anodizing mainly uses three of them: sulfuric acid, chromic acid, and oxalic acid. These three electrolytes will increase the current, which will make the anodic oxidation more thorough.
6. Anodizing Production Process
The production process of anodized aluminum is divided into 5 steps in total.
- Parts are first polished. This step is to ensure that the part can fully react with the solution chemically, and it is also convenient for later coloring treatment.
- After mechanical polishing, chemically remove the copper component on the surface of some alloys.
- The third step is to clean and remove the oil. Re-clean the parts to remove the oil stains on the surface. It should be specially pointed out that for the parts that have been anodized if the factory insists on re-anodizing treatment, alkali or special agents should be used as cleaning agents.
- In the fourth step, put the processed parts into a dilute sulfuric acid solution as an anode to energize until a surface oxide layer is formed (the oxide layer is porous and is a white translucent film).
- The fifth step is dyeing, which can be fixed after dyeing.
Introduction of Five Advantages of Aluminum Anodizing Manufacturers to Their Products
- As the Bottom Layer of Spray Painting and Electroplating: Because the oxide film layer has porosity and good adsorption capacity, it has a good bonding force with paint film and organic film, and can be used as the bottom layer of spray paint. The film layer anodized with aluminum phosphate can be used as the bottom layer of electroplating on aluminum.
- Prevent Product Corrosion: Since the film layer obtained by aluminum machining has been properly sealed, it has good stability in the atmosphere. Whether it is obtained from the sulfuric acid solution, oxalic acid solution, or chromic acid solution in the normal process of aluminum anodic oxide film, its corrosion resistance is very good.
- Protection-Decoration: On the oxide film with high transparency, the oxide film has the characteristics of adsorbing various organic dyes or inorganic pigments, and various bright bright colors and patterns can be obtained on the oxide film. Coupled with the emergence of many new processes in recent years, such as one-time oxidation for multiple coloring, fireworks patterns, wood grain patterns, oxidation offset transfer printing, porcelain oxidation, etc., the appearance of aluminum is more beautiful and pleasing to the eye. This layer of color film is a decorative layer. It is also an anti-corrosion layer, such as lighters, gold pens, and handicrafts.
- As A Hard Wear Layer: In sulfuric acid or oxalic acid solution, a thick and hard film can be obtained by adjusting the process conditions of anodizing. The pores and absorption properties of the film layer are used to store the selected oil, which is effectively used in working conditions under friction, and has the characteristics of lubrication and wear resistance, such as engine cylinders and pistons of automobiles and tractors.
- As An Electrically Insulating Layer: The aluminum anodized film layer has the characteristics of high resistance, and the thickness of the film layer is proportional to the resistance. This feature has certain practical significance as electrical insulation. It can be used as a dielectric for capacitors, and aluminum oxide can also be used for cables. The outer covering is used as an insulating layer on its surface to replace the plastic covering and plastic covering. If the phenolic resin is used as the film hole filling, its breakdown voltage can be increased by 2 times. In oxalic acid solution, when the film thickness increases, a high-quality insulating layer with a resistance of 200Ω and a breakdown voltage of 980V can be obtained. Of course, this feature is used. In addition to being used for wires, it can also be used for other electrical appliances.
Is Anodizing Right For You?
As one of the most common materials, aluminum has a wide range of applications in construction, industry, rail transit, photovoltaic power generation, and other fields. With the rapid development of new infrastructure, China’s total aluminum production will increase significantly in 2021. The output of alumina, electrolytic aluminum, and aluminum will be 73.13 million tons, 37.08 million tons, and 57.79 million tons, up 0.3%, 4.9%, and 8.6% respectively.
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