Anodizing is one of the most commonly used surface treatment processes for CNC aluminum machining parts. It forms a protective oxide layer on the surface of the aluminum parts, enhancing their corrosion resistance, wear resistance, surface hardness, and appearance, while maintaining dimensional accuracy.
This article will introduce the working principle, advantages, machining processes, and applicable materials of anodizing, helping you determine whether anodizing is suitable for your CNC parts.
What Is Anodizing
Anodizing is an electrochemical process that converts the surface of aluminum parts into a durable aluminum oxide (Al₂O₃) layer. During the process, your CNC aluminum part is connected to the positive terminal of a DC power supply and serves as the anode in an electrolyte solution.
When an electric current is applied, oxygen ions react with aluminum to form a protective oxide layer that is integrated with the base material, rather than being applied as a separate coating.
Among various aluminum finishes, anodizing is one of the most popular choices for CNC machined aluminum parts because it improves both performance and appearance.
Common Types of Anodizing
Depending on the electrolyte and process, anodizing mainly falls into two types: Type II and Type III. These different types vary in terms of film thickness, wear resistance, corrosion resistance, and application scenarios.
Type II is the most common anodizing process in CNC machining, using sulfuric acid as the electrolyte. It can provide your parts with excellent corrosion resistance and a wide range of color options, while also being relatively cost-effective.
Type III is also known as Hard Anodizing. It is typically formed by using lower temperatures and higher current densities to create a thicker and harder oxide film, thus offering superior wear resistance and durability. If the parts you design need to remain in harsh environments for an extended period, you might consider this option.
| Type | Type II | Type III |
| Electrolyte | Sulfuric acid | Sulfuric acid (under low temperature and high current density conditions) |
| Film thickness | Medium | Thick |
| Corrosion resistance | Good | Excellent |
| Durability | Good | Excellent |
| Dyeability | Excellent | Limited |
| Dimensional impact | Medium | Significant |
| Main application | Electronic product casing Instrument and equipment casing Keyboard casing Consumer electronic products Industrial parts | Mechanical parts Automobile components Hydraulic elements Industrial equipment Aerospace parts |
If your parts pay more attention to appearance, color, and corrosion resistance, Type II Anodizing is a good choice.
Type III Hard Anodizing provides higher surface hardness and longer service life if your part has to withstand greater friction, wear, or harsh environments.
You can choose the appropriate anodizing process based on your actual situation.
Anodizing Process for CNC Machining Parts
Step 1: CNC Machining
Based on your finalized drawings and tolerance requirements, your CNC turning parts and milling parts are first machined to achieve the required dimensions, geometric accuracy, and surface quality. High-quality machining ensures a uniform anodized finish for your parts.
Step 2: Deburring and Surface Preparation
After CNC machining is completed, it is necessary to remove burrs from the parts, and the parts are degreased, cleaned, and dried to remove oil, natural oxide layers, and other impurities. A clean and uniform surface ensures uniform formation of the oxide film and improves color consistency and surface quality.
Step 3: Anodizing
The aluminum part is connected to the positive terminal of a DC power supply so that it acts as the anode, and then immersed in the electrolyte. After applying an electric current, an electrochemical reaction occurs on the surface of aluminum, forming a hard, dense, and firmly bonded protective film of aluminum oxide on the substrate.
Step 4: Coloring
If your parts have requirements for the appearance color, you can select the color you want from the Pantone color system in advance and dye it before sealing the oxide film. If you need to anodize aluminum black, black is one of the most popular color options for CNC aluminum parts. Because the surface of the oxide film has many tiny pores, the dye can penetrate into them, resulting in a lasting and uniform color while preserving the metallic texture of the aluminum material.
Step 5: Sealing
After dyeing your CNC parts or completing natural color anodizing, perform a sealing treatment on the oxide film to seal the micro-pores on the surface. It can further improve the corrosion resistance, pollution resistance, and color stability of your parts, thereby extending the service life of the parts.
Step 6: Quality Inspection
Finally, your parts undergo a comprehensive quality inspection, including appearance inspection, color consistency, film thickness measurement, and critical dimension verification using precision measuring equipment such as a CMM, ensuring they meet your quality requirements.
Benefits of Anodizing CNC Parts
Improve corrosion resistance
Anodizing forms a hard and dense protective aluminum oxide layer on the surface of CNC aluminum parts, thereby enhancing the corrosion resistance of the component. This enables your part to better adapt to humid, outdoor, and general industrial environments, thus prolonging its service life.
Enhance Surface Protection
Anodizing forms a hard and dense oxide film on the surface of CNC aluminum parts, increasing the surface hardness of the parts and enhancing their wear resistance. This protective film can enhance scratch resistance, reduce surface damage caused by frequent friction, contact, or repeated assembly, and help the parts maintain good appearance and performance while extending service life.
Improve insulation performance
If your parts require a reduction in surface conductivity or an improvement in electrical insulation performance, anodizing can form an insulating layer of aluminum oxide on the surface of CNC aluminum parts. This insulating oxide layer can help reduce electrical conductivity on the surface, making it suitable for certain electronic and industrial applications.
Improve decorative effects
Anodizing not only enhances the performance of your CNC aluminum parts, but also improves their appearance. Through the dyeing process, parts can be customized in color according to the Pantone color. While maintaining the unique metallic texture of the aluminum material, it also becomes more aesthetically pleasing.
Disadvantages of Anodizing CNC Parts
Additional Cost and Lead Time
Anodizing is a post-machining step. You need to add pre-treatment, oxidation, dyeing (if necessary), sealing, inspection, and other procedures, which will increase the machining cost and production cycle.
Limited Material Compatibility
Anodizing is mainly applicable to aluminum and aluminum alloys. Some titanium and magnesium alloys can also undergo anodizing through different processes. However, if the raw materials of your parts are steel, stainless steel, copper, and other materials, traditional anodizing processes cannot be applied effectively. Therefore, you need to choose the appropriate surface treatment method according to the material.
Affects Part Dimensions and Assembly Accuracy
Anodizing forms an oxide film on the surface of aluminum parts, which will have a certain impact on the dimensions of the parts. For high-precision CNC parts, you need to reserve the corresponding dimensions during the design phase to ensure that the anodizing can still meet the assembly and tolerance requirements.
This mainly affects precision mating parts, threads, shaft-hole fits, and components with tight tolerances.
Color Variation Between Alloys
Even with the same anodizing process, different aluminum alloys may have different final colors and glosses due to their varying chemical compositions. Therefore, if you have a high requirement for appearance consistency, it is recommended that you use materials from the same batch for CNC machining.
Complex Geometries May Affect Coating Uniformity
For parts with sharp corners, deep holes, blind holes, or complex geometries, the current distribution during the anodizing process may be uneven, resulting in inconsistent film thickness and affecting the appearance or local performance. Therefore, you should consider anodizing process requirements in the product design stage.
What Materials Can Be Anodized
6061
6061 aluminum is one of the most commonly used materials in CNC machining and anodizing. It has good machining properties, mechanical properties, and corrosion resistance. After anodizing, it can form a uniform and dense oxide film with good anodizing performance and is widely used in CNC applications. It is mainly used in consumer electronic product shells, CNC mechanical parts, auto parts, industrial equipment structure parts, instrument and meter shells, CNC aluminum alloy keyboard shells, and other structural parts and precision CNC parts.
6063
6063 has excellent anodizing properties. If you have high requirements for surface quality and appearance, this is your ideal raw material choice. Due to the moderate content of silicon and magnesium, a uniform and fine oxide film can be formed after anodizing, which has good color consistency and decorative effect. Therefore, it is widely used in aluminum alloy shells and panels, architectural decorative profiles, LED lamp shells, instrument and equipment shells, high-end appearance parts, and decorative parts.
5052
5052 is known for excellent corrosion resistance, especially suitable for wet, marine, and chemical environments. It can be anodized and form a good-quality oxide film. Although the color consistency after dyeing is usually not as good as that of 6063, if your parts need to be exposed to harsh environments for a long time, its excellent corrosion resistance is your ideal choice. Currently, it is mainly applied in marine equipment components, ship accessories, automotive sheet metal parts, and other places.
7075
7075 is a high-strength aluminum alloy that is widely used in CNC precision parts with high mechanical performance requirements. It has an excellent strength-to-weight ratio and good fatigue resistance. After anodizing, it can form a protective oxide film, enhancing the corrosion resistance and surface wear resistance of the parts.
Due to its high zinc and copper content, 7075 may have limited color consistency after anodizing. It is suitable for parts requiring high strength and anodizing, but performance and appearance requirements should be balanced. Common applications include aerospace components, high-strength mechanical parts, and industrial equipment.
Titanium
Titanium and titanium alloys can also undergo anodizing. By controlling the thickness of the oxide film, various colors such as blue, purple, and gold can be produced, which can enhance corrosion resistance and biocompatibility. Titanium anodizing is also widely used in medical and aerospace applications.
Although anodizing is possible for several metals, aluminum and its alloys are by far the most commonly anodized materials in CNC machining due to their excellent corrosion resistance, appearance, and machinability.
Does Anodizing Affect CNC Part Assembly?
For CNC precision parts, the dimensional changes after anodizing are one of the issues you need to consider. If you do not incorporate dimension compensation during the design and machining stages, the anodizing process may affect the assembly accuracy of your parts.
Anodizing is not simply adding a coating to the surface of a part, but converting the aluminum surface into an aluminum oxide layer. The oxide film occupies a certain space, thus changing the actual size of the part.
In fact, you don’t need to worry too much. As long as you fully consider the size changes brought about by anodizing during the product design and CNC machining stages, and adopt reasonable size compensation, most CNC parts can be assembled normally after anodizing.
FAQ
Q: What are CNC anodizing services?
A: CNC anodizing service combines precision CNC machining with anodizing surface treatment to provide customers with aluminum alloy parts manufacturing services with controllable size, stable color, and improved performance.
Q: What Is Anodizing and Why Is It Important for CNC Aluminum Parts?
A: Anodizing forms a dense layer of aluminum oxide (Al₂O₃) on the surface of CNC aluminum parts, enhancing the parts’ corrosion resistance, wear resistance, and surface durability, providing additional protection that can’t be achieved through simple CNC machining.
Q: What products typically undergo anodizing for enhanced corrosion resistance?
A: Anodizing is commonly used for CNC aluminum parts, including electronic housings, mechanical components, automotive parts, aerospace components, and industrial equipment parts that require improved corrosion resistance and surface durability.
Q: Is anodizing better than powder coating?
A: Anodizing forms a stronger bond with the base material, preserving the metallic texture, and is not prone to peeling off.
Powder coating offers a wider range of colors and a thicker coating layer.
It mainly depends on the application choice of your parts
Q: How long can anodizing last?
A: The service life of anodizing depends on several factors, mainly including film thickness, usage environment, material, and post-treatment.
Normal industrial applications can maintain their performance for a long time.
Q: Can you provide CNC machining and anodizing as a one-stop service?
A: Of course. We provide one-stop CNC machining and anodizing services, helping you reduce communication costs, shorten lead times, and maintain consistent quality from machining to surface finishing.
Final Thoughts
Shanghai Yecheng specializes in precision CNC machining and anodizing for aluminum parts. With in-house machining and anodizing, we ensure consistent quality, color, and precision. We look forward to becoming your reliable long-term manufacturing partner.
