Anodizing is a surface treatment process commonly used on metal parts to enhance corrosion resistance, wear resistance, and surface appearance. However, not all metals suit conventional anodizing.
This article will introduce which metals can undergo anodizing, with a focus on aluminum and common aluminum alloys.
What is Anodizing?
Anodizing is an electrochemical surface treatment process that is mainly used to form a controlled oxide layer on the surface of metals. During the anodizing process, metal parts are typically connected as the anode to the positive terminal of the power supply and placed in a suitable electrolyte solution.
After being electrified, the metal surface undergoes an oxidation reaction and gradually forms an oxide layer. The film layer formed by anodizing can modify the performance of the metal surface of the CNC parts you design:
- Enhance corrosion resistance
- Improve wear resistance
- Improve appearance
- Provide electrical insulation
- Maintain the metallic texture
Type of Anodizing
If the CNC metal parts you design need to meet requirements for appearance, corrosion resistance, and dimensional accuracy, the choice of anodizing type will directly affect the surface performance and appearance of the final parts.
Different types of anodization have different film thicknesses and surface characteristics. Understanding the basic differences between Type I, Type II, and Type III can help you understand the surface effects produced by different anodizing processes.
| Anodizing Type | Film Thickness | Key Characteristics |
| Type I | Approx. 0.5–18 μm | Thinner coating with good corrosion resistance and minimal dimensional change |
| Type II | Approx. 5–25 μm | The most common type of anodizing; can be dyed and provides a balance of appearance, corrosion resistance, and surface protection |
| Type III | Approx. 25–50 μm or higher | Thicker coating with higher hardness and wear resistance, as well as good corrosion resistance |
The thickness ranges below are approximate and can vary depending on the specification, alloy, and anodizing process.
What Metals Can Be Anodized?
If you are designing CNC metal parts and plan to perform anodizing after machining, you must first confirm whether the selected material is suitable for this surface treatment.
Aluminum and Aluminum Alloys
Aluminum is the most common material used for anodizing CNC parts. During anodizing, aluminum can form an oxide film on the surface, mainly composed of aluminum oxide. This oxide film has a porous structure and can be dyed, and it can produce different surface colors and appearances.
Common CNC aluminum alloys, such as 6061, 6063, 7075, 2024, and 5052, can all undergo anodization. However, you should be aware that the composition of different aluminum alloys varies, so the structure of the anodic oxide layer, color, luster, and surface uniformity may also differ.
For example, 6061 and 6063 usually result in a relatively uniform anodized appearance, while 7075, 2024, and other materials with more alloy elements may have different anodized colors and surface performances.
Therefore, even if you choose all aluminum alloys, you cannot assume that they will all produce exactly the same results after anodization.
Titanium and Titanium Alloys
When the CNC titanium parts you design require anodizing, an oxide film mainly composed of titanium oxide will form on the metal surface. By controlling the electrochemical treatment conditions, the thickness of the oxide film can be changed, thereby producing different surface colors.
Unlike anodized aluminum, titanium anodizing does not normally rely on dyes to produce its characteristic colors. The color of titanium anodizing mainly comes from the optical interference effect produced by the oxide film.
Therefore, when you design titanium CNC parts and need a specific color, the final color will be affected by factors such as the material, surface condition, and anodizing parameters.
Magnesium and Magnesium Alloys
Magnesium alloys can be anodized using specialized processes, but the treatment is different from conventional aluminum anodizing. Magnesium has a high degree of chemical reactivity, so in the anodizing process, specific electrolytic systems and process conditions tailored for magnesium alloys need to be used. After treatment, an oxide layer or related protective film can be formed on the surface of the magnesium alloy.
If the parts you design are made of magnesium alloys, you should be aware that the chemical composition of different magnesium alloys can affect the formation of the oxide film and the final surface condition.
Other Metals
Some special anodizable metals, such as niobium, zirconium, and tantalum, can also form oxide films through specific electrochemical processes. Some of these materials can obtain different colors by utilizing the optical properties of the oxide films.
These metals differ significantly from aluminum anodizing in terms of the composition, formation mechanism, and color manifestation of the oxide films. Therefore, when you hear that a certain metal “can be anodized”, it does not mean that it can directly undergo the processing method of aluminum anodization.
| Metal Material | Can Be Anodized? | Color Options | Main Applications |
| Aluminum & Aluminum Alloys | ✔ | Black, silver, gold, red, blue, and other custom colors | CNC parts, housings, panels, structural components |
| Titanium & Titanium Alloys | ✔ | Blue, purple, gold, green, cyan, and other colors | Medical parts, decorative components, precision parts |
| Magnesium & Magnesium Alloys | Yes, but requires specialized processes | Gray, black, and other limited colors | Aerospace, automotive |
| Niobium | ✔ | Blue, purple, green, gold, and other interference colors | Jewelry, decorative components |
| Zirconium | ✔ | Blue, purple, green, gold, and other interference colors | Medical, jewelry |
| Tantalum | ✔ | Mainly interference colors, with a wide range of possible colors | Medical, electronics, and specialized industrial components |
FAQ
Can You Anodize Steel?
Carbon steel, stainless steel, and most steel materials are generally not suitable for conventional anodizing processes.
How to Choose a Metal for Anodized CNC Parts?
For aluminum alloy parts, you also need to pay attention to the specific alloy grade, as the composition of different alloys will affect the formation of the anodized film and the final color, luster, and surface uniformity.
Therefore, when determining the material, you not only need to confirm whether it can be anodized, but also need to understand the specific surface performance of the material after anodization.
Is an Anodized Finish Durable?
The anodized surface usually has good durability. The oxide layer bonds metallurgically to the base metal, delivering reliable scratch and corrosion resistance for most CNC applications.
Does Anodizing Wear Off?
Under normal circumstances, the anodic oxide film is not prone to peeling off. However, after prolonged friction, scraping, or other mechanical wear, the oxide film will gradually wear down.
Can I Get The Same Anodized Color On Different Aluminum Alloys?
Not necessarily. Even when the same anodizing dye and process are used, different aluminum alloys can produce different shades, gloss levels, and surface appearances.
What is the 720 rule for anodizing?
The 720 rule is a commonly used estimation method for calculating anodizing time and coating thickness based on current density. Actual results vary with the alloy, electrolyte, temperature, and process conditions.
Final Thoughts
If you are unsure whether your material is suitable for anodizing, or need to understand how an aluminum alloy may affect the final color and surface finish, our engineering team can review your drawings and material requirements before production.
