In the machining and casting industries, most molded parts products will undergo the step of anodizing. This is an electrochemical process that can form an oxide film on the metal surface to improve the quality of the parts, and this process is usually used in aluminum and its alloys. Today I will tell you in detail about the specifics.
How Does Anodizing Work?
1. Prepare
First, the parts need to thoroughly clean their metal surface to remove oil, dust and other contaminants on the surface. You should know that this step is actually important to ensure the uniformity and adhesion of the oxide film.
2. Electrolysis Process
The cleaned metal parts are connected to the entire circuit, called an anode, and then immersed in an electrolyte containing chemical compounds, usually sulfuric or chromic acid. Once the parts are fixed and do not move, the metal connected to the negative electrode can be put in, so that the oxidation reaction will occur when the electricity is applied.
3. Oxide Film Formation
You need to understand that this step is the core of the entire anodizing process. The negative electrode on the part attracts positive ions in the part, while the negative oxygen ions (anions) in the solution are attracted to the aluminum part. At this time, aluminum atoms on the metal surface react with oxygen ions in the electrolyte to form aluminum oxide (Al₂O₃). In this way, a hard oxide film can be gradually formed on the surface of the metal.
In addition, the thickness of the oxide film can also be controlled by adjusting the current density and processing time. This thickness can be between a few microns and a few hundred microns.
4. Post-Treatment
After the oxide film is formed, the part can be dyed to change its color. Then it is necessary to enhance the sealing and corrosion resistance of the oxide film through sealing treatment (such as hot water sealing or chemical sealing).
5. Performance Improvement
After completing the entire surface treatment process, the parts are ready to be used. Just like your experience after use, the corrosion resistance and wear resistance of anodized parts can be said to be greatly improved compared to before, effectively increasing the service life. At the same time, the aesthetics are also quite good.
Types Of Anodizing
What you may not know is that there are actually many types of anodizing, each type is used for different uses and needs.
1. Sulfuric Acid Anodizing
The most common type of anodizing in the industry, dilute sulfuric acid is used as the electrolyte. The thickness of the film layer is usually between 5 and 25 microns. This type of anodizing method is very suitable for precision components and can provide excellent corrosion and wear resistance without significantly changing the size of metal parts, so it is generally used in aerospace, automotive and construction fields.
2. Oxalic Acid Anodizing
Oxalic acid anodizing uses oxalic acid as the electrolyte, and this type of anodizing produces a relatively thin and smooth oxide film. The thickness of the film layer is usually between 5 and 20 microns, and the application fields are generally in industries with requirements for appearance, such as home appliances and decorative aluminum.
3. Phosphoric Acid Anodizing
This type of oxidation uses phosphoric acid as the electrolyte, thereby enabling a thicker film layer, usually between 20 and 50 microns. The result is that the wear resistance of the parts can be greatly improved.
4. Ammonium Sulfate Anodizing
If you work in the field of tools and mechanical components, then you need to know that ammonium sulfate anodizing is very suitable for high wear resistance and high corrosion resistance. It uses ammonium sulfate as the electrolyte, so the film layer of the part is thicker and harder, often between 20 and 100 microns, so that your mechanical tools can resist fabrication.
5. Micro-Arc Anodizing
Micro-arc Anodizing, also known as plasma anodizing, uses high voltage to create a microporous film layer. The hardness of the film produced by this oxidation method is extremely high, generally between 20 and 100 microns. It is precisely because of this attribute that it is suitable for fields with extremely high performance requirements, such as aerospace and military.
6. Colored Anodizing
I believe that many of you have the need to dye parts, so you need to understand this method of coloring anodizing. Its characteristic is that it is dyed after anodizing and can adopt a variety of colors. This type of oxidized building decoration, home appliances and consumer products has been widely used in industries, which has greatly improved the appearance of the product.
Parameters And Properties Of Anodizing
It can be said that the process of anodizing involves multiple parameters and properties, and these parameters and properties directly affect the quality and performance of the oxide film. I will explain it to you one by one below.
1. Main Parameters
(1)Types Of Electrolytes
Commonly used electrolytes include dilute sulfuric acid, oxalic acid and phosphoric acid. Different electrolytes affect the thickness and properties of the film layer.
(2)Current Density
Current density refers to the intensity of current applied per unit area, often expressed in amperes per square meter (A/m²). As for the choice of current density, it will affect the growth rate and uniformity of the film layer.
(3)Processing Time
The anodizing time is usually between minutes and hours. The longer the time, the thicker the film layer will be, but at the same time, it may also cause the quality of the oxide film of the parts to decrease.
(4)Temperature
The temperature of the electrolyte will affect the rate of reaction. Higher temperatures usually speed up the oxidation process, but may also affect the quality of the oxide film.
(5)Film Thickness
The film thickness is usually between 5 microns and 100 microns. The larger the thickness, the stronger the corrosion resistance and wear resistance.
2. Main Properties
（1）Corrosion Resistance
The anodic oxide film has good corrosion resistance and can effectively prevent oxidation and corrosion of parts.
（2）Wear Resistance
The oxide film has a high hardness and can provide good wear resistance. Parts with this property are ideal for you to use in high wear environments.
（3）Insulation
The anodic oxide film has good electrical insulation and is very suitable for electronic and electrical applications.
（4）Aesthetics
It can provide a variety of colors and luster to enhance the appearance of the product.
（5）Breathability
The anodized film also has a certain degree of breathability, allowing certain gases and water vapor to pass through, but can still ensure good protection.
Which Metals Can Be Anodized?
Since all this has been said, you will definitely have doubts about which metals are suitable for anode maintenance. Don’t worry, i will tell you this.
1. Aluminum and aluminum alloy
The most common anodized metal has good conductivity. After the metal is processed, a layer of alumina can be formed, which greatly improves wear resistance and corrosion resistance. It also supports the choice of multiple colors to improve appearance.
2. Titanium
After titanium is anodized, it can form a corrosion-resistant oxide film on the metal surface, and its biocompatibility is also very good. At the same time, the metal also supports a variety of colors without using dyes.
3. Magnesium
Magnesium is not common, but after anodizing, it also improves its corrosion resistance and surface hardness. There is only one thing that is, it is difficult to treat magnesium.
4. Zinc
After the anodizing treatment of zinc, it can improve its corrosion resistance and surface finish, and its surface performance can be said to be well improved.
5. Lead
Lead is far less common than aluminum and titanium, but the metal also improves its surface properties after anodization.
Cost Of Anodizing
So now let’s talk about the cost issue that you are very concerned about. How much does an anodizing treatment cost? In fact, the cost of anodizing varies depending on several factors, here are the main ones:
- Material cost: Different material choices will affect material cost and processing time
- Anodizing type: Different treatment methods naturally have different costs.
- Part complexity: The more complex the parts are, the longer the processing time will be, and the overall cost will also increase.
- Film layer thickness: The larger the film layer thickness, the longer the processing time, and the cost will increase accordingly.
- Processing scale: Large batch processing can usually reduce the cost of a single piece, but the unit cost will be higher for small batches or single pieces.
- Color Surface Treatment: Add dye to get a specific color, which will add extra cost
- Additional surface treatment: Such as polishing and cleaning, it will also increase costs
- Regional price: Different regions will also have differences in price
Benefits Of Anodizing
Next, I will explain the benefits of anodizing to you in detail.
1. Corrosion Resistance
The oxide film can effectively resist the invasion of oxygen and moisture, thereby improving the corrosion resistance of parts.
2. Wear Resistance
The hardness of the oxide film is usually relatively high, which can significantly increase the hardness of the surface of the part, thereby extending the service life of the product.
3. Improved Appearance
Anodizing can achieve multiple colors through dyeing, improving the aesthetics of the product, thereby meeting your different design needs.
4. Environmental Friendliness
In fact, the environmental protection of anodizing is also very good, and it does not use harmful chemicals, which is very in line with the requirements of modern industry for sustainable development.
5. Non-Toxicity
The coating is non-toxic, so anodizing is very suitable for use in the consumer goods industry.
6. Electrical Insulation
Because the oxide film has good electrical insulation properties, anodizing is also widely used in electronic equipment and electrical industries.
Applications Of Anodizing
Because anodizing can provide excellent surface performance to parts, it is widely used in many fields, and the following is to introduce it to you one by one.
1. Industrial Applications
- Aerospace: Anodizing is used in aircraft components to improve their corrosion resistance and wear resistance
- Automotive industry: Automotive parts (such as wheel hubs, body frames, etc.), anodizing can improve their corrosion resistance and appearance.
- Electronic equipment: After anodizing, the insulation protection and corrosion resistance of electrical and electronic components have been significantly improved.
2. Architecture And Decoration
- Building Materials: Anodized aluminum is used on building materials such as window frames, doors and curtain walls, thus providing aesthetics and weather resistance.
- Interior Decoration: Anodizing can provide a variety of color options and wear resistance in furniture, lamps and other interior decorations.
3. Home Appliances
- Kitchen utensils:Kitchen utensils such as pots and baking trays. After anodization, it can bring a wear-resistant and corrosion-resistant surface.
- Electrical housing: The shell of refrigerators, washing machines and other home appliances. Anodizing can enhance its durability and appearance.
4. Medical Devices
Medical Equipment: Anodizing is used in medical devices (such as surgical instruments and implants) can provide biocompatibility and corrosion resistance
5. Sports And Leisure Goods
- Sports equipment: such as bicycle frames, snowboards and golf clubs, anodizing can improve their strength and appearance.
- Outdoor equipment: such as tent brackets, mountaineering equipment, etc., which are corrosion-resistant and lightweight.
Conclusion
In short, anodizing can be said to be an indispensable part of the surface treatment process in modern industry. It can significantly improve the surface properties of the parts, thereby greatly enhancing the service life of the parts. If you have any needs for this, please come to communicate with our DSR company with 14 years of machining and manufacturing experience, we are waiting for your letter!
Frequently Asked Questions
Q1: What metal cannot be anodized?
Many metals are illegally anodized, such as: iron, steel, copper, nickel, tin, and tungsten steel. None of these metals can form stable and durable oxide layers by anodizing.
Q2: What chemical is used in anodizing?
A: Commonly used chemical substances include sulfuric acid, nitric acid, oxalic acid and phosphoric acid.
Q3: How long does anodizing last?
A: The durability of anodizing is generally between 5 and 30 years, depending on factors such as film thickness, usage environment, material type and post-maintenance. And under appropriate conditions, anodizing can significantly extend the service life and performance of the parts.
Q4: How do I assess the quality of anodized parts?
A: The first is visual observation. You need to observe whether the surface of the part is uniform, whether there are bubbles, peeling or other defects, etc. For dyed parts, it is necessary to observe whether their color is uniform and whether there is color difference.
Secondly, you need to use professional testing instruments to test the resistance of parts to wear, corrosion, and conductivity, and to evaluate whether they meet the quality standards.
Finally, according to your own use needs, you can use measuring instruments to measure whether the film thickness of the part meets your requirements.
Q5: Can a part be secondary anodized?
A: Yes. But before you do secondary anodizing, the original oxide film and any dirt, grease or other contaminants need to be removed. It is also worth noting that if the original anodizing treatment quality of the part is poor, the secondary treatment may not significantly improve its performance.
Q6: What colors can be used for anodizing？
The colors available are natural (silver gray), black, red, blue, green, yellow, purple, gold and white.
