What is Anodizing?
Anodizing is an electrolytic process that deposits a chemically stable oxide layer on the surface of aluminum. The resulting oxide film is thicker and stronger than the natural oxide coating of aluminum. It is hard, porous, and transparent, and is an integral part of the metal surface, so it will not peel or peel off. Once deposited, the oxide film can be colored in a variety of ways before sealing.
The thickness of the film is graded, and its grade specification depends on the application, ranging from 5 microns to 25 microns. Decorative decoration applications usually use a thickness of 5 microns, and interior applications use a thickness of 10 or 15 microns. The external finish requires a film thickness of 25 microns. Anodizing is suitable for extrusion, casting, rolling, drawing and forging aluminum products.
Anodizing’s Benefits
The thickness of the oxide film obtained by anodizing treatment is generally 5-20um, and the thickness of the hard anodizing film can reach 60-2500um. And what will this anodic oxide film bring us?
Improve corrosion resistance.The anodic oxide film of pure aluminum has better corrosion resistance than that of aluminum alloy. This is due to the inclusion of alloy components or the formation of metal compounds that cannot be oxidized or dissolved, resulting in discontinuity or voids in the oxide film, which greatly reduces the corrosion resistance of the oxide film. Therefore, in general, the film obtained after anodic oxidation must be sealed to improve its corrosion resistance.
Surface coloring of decorative aluminum products. Before the aluminum profile is anodized and sealed, there will be a lot of dense pores on the surface, which can easily absorb some metal salts or dyes, so that the surface of the aluminum products can form colorful colors.
Higher hardness.The hardness of the anodized film is much higher than that of the aluminum substrate: the hardness of the substrate is about HV100, the hardness of the ordinary anodized film is about HV300, and the hardness of the hard anodized film can reach about HV500.The anodic oxide film not only has higher hardness, but also has better wear resistance. In particular, the porous oxide film on the surface layer has the ability to adsorb lubricant and can further improve the wear resistance of the surface.
Strong adsorption capacity. The anodic oxide film of aluminum and aluminum alloy has a porous structure and has a strong adsorption capacity, so filling the pores with various pigments, lubricants, resins, etc. can further improve the protection, insulation, wear resistance and decoration properties of aluminum products.
Very good insulation performance. The anodic oxide films of aluminum and aluminum alloys no longer possess the conductive properties of metals and become good insulating materials.
Excellent thermal insulation and strong heat resistance. This is because the thermal conductivity of anodized film is much lower than that of pure aluminum: anodized film can withstand a temperature of about 1500°C, while pure aluminum can only withstand 660°C.
The anodic oxide film and the electrochemical process used to produce the anodic oxide film should be harmless to the human body. Therefore, in order to reduce the weight of the products, the convenience of machining, and the environmental protection and low toxicity requirements in many industries, some parts of the current products are made of aluminum alloy hard oxidation instead of stainless steel, hard chromium plating and other processes.
Multi-color anodized
Color Anodizing
Commonly used materials for anodizing
Aluminum and aluminum alloys, common ones are: 2A12, 5052, 6061, 6063, 7075, etc.; in addition, cast aluminum alloys, such as ADC10, ADC12, A356, A380, etc., are often anodized;
Magnesium alloy: mainly used for conductive oxidation/chemical oxidation, the colors are white and yellow;
Titanium alloy: Titanium alloy is anodized and can be made in various colors, such as blue, yellow, green, gold, etc.
Process conditions and requirements of anodizing treatment
There are many types of solutions used in anodizing treatment. Currently, the commonly used ones are: sulfuric acid, oxalic acid, oxalic acid plus sulfuric acid, malonic acid and sulfosalicylic acid. One of the most common methods is to use sulfuric acid as the oxidation treatment solution and electrify for anodizing. This method is usually referred to as sulfuric acid anodizing.
Advantages of sulfuric acid anodizing:
- In addition to obtaining a dense oxide film, the oxide film has a large porosity, which can better impregnate fillers, and has a wide range of aluminum materials suitable for the oxidation treatment method. At the same time, the operation process is simple, the cost is low, and the power consumption is low. Therefore, sulfuric acid anodizing is used in many cases.
When sulfuric acid anodizing is used, the following factors that affect the quality of the oxide film should be considered:
- Concentration of sulfuric acid oxidation treatment solution
- water
- The temperature of the oxidation treatment solution
- Current density
- Initial and final voltage and processing time
- Stirring speed of oxidation treatment solution
- Anodic oxidation in chromic acid electrolyte
- Anodic oxidation in oxalic acid electrolyte
Start Your Project Today
When you send us a 3D CAD file, our sales staff will evaluate the quotation for you according to your customization requirements, and hope to receive your email. Contact us immediately to get a competitive discount.
