Depending on the products you design and develop, the surface treatment will directly affect the appearance, durability, functionality, cost, and user experience.
If surface treatment is not considered in advance, it may cause your products to have scratches, oxidation, fingerprints and dents.
This article will introduce 9 CNC aluminum surface finish types in CNC machining.
Different Surface Finishes For Aluminum
Type 1: As Machined Finish
Surface finish plays a crucial role in your product. If you keep the finish raw, you can clearly see tool marks on the surface.
Type 2: Bead Blasting/ Sand Blasting
The main purpose of sand blasting or bead blasting is to remove the tool marks from the surface. Usually, we will also apply anodizing in the subsequent processing.
It is widely used in electronic parts, enclosures, and keyboard parts.
If you are looking for a matte texture, you can consider sand blasting for your product. Depending on the different requirements for surface fineness, there are different types of sand blasting, such as 150 grit, 180 grit, 200 grit, etc.
Type 3: Anodizing Aluminium Finish
We use two anodizing types for aluminum parts.
The first one is Type II anodizing (standard anodizing).
And the second type of anodizing we mentioned is the type III anodizing, which is also named as hard anodizing. It can enhance the hardness of the part and directly convert the aluminum surface into a hard, dense oxide layer.
Therefore, the wear resistance and scratch resistance of your part will be stronger. However, it also has some limitations. Usually, the colors we can choose for the hard anodizing are relatively limited.
The following table lists the differences between the hard anodizing and the ordinary anodizing for your reference.
Type II Anodizing vs Type III Hard Anodizing
| Category | Standard Anodizing (Type II) | Hard Anodizing (Type III) |
| Core Purpose | Appearance + basic protection | Functional performance + high wear resistance |
| Surface Hardness | ~200–400 HV | ~400–600 HV |
| Wear Resistance | General | Very high (typically 2–5× higher than Type II) |
| Coating Thickness | ~5–25 μm | ~25–100 μm |
| Color Capability | Wide range (custom colors available) | Limited (mostly dark tones such as grey, black, gunmetal) |
| Dimensional Impact | Low (typically +5–15 μm per surface) | Higher (typically +10–50 μm per surface) |
| Typical Applications | Consumer electronics / CNC housings | Industrial parts / sliding or wear components |
Type 4: Powder Coating
Powder coating is a common surface treatment method for aluminum materials. Through this method, you can achieve a wide range of color and texture options (such as matte, high gloss, metallic texture, etc.), making it suitable for products with high customization requirements for appearance.
However, you should be aware that the thickness of the powder coating layer is relatively high, which may affect the assembly tolerance. Therefore, the key mating surfaces need to be reserved or shielded in advance. At the same time, the powder coating is an insulating layer. If your product requires conductive or grounding functions, you must plan the local shielding areas in advance.
It is more suitable for applications such as electronic enclosures, automotive exterior parts, outdoor equipment, and industrial structural components.
Type 5: Polishing
This is also a common surface treatment for aluminum materials. You can achieve a mirror or semi-mirror finish effect through polishing.
However, since polishing is a subtractive process, it is particularly important to maintain dimensional tolerances and edge quality.
When choosing this process, you must be cautious because the mirror surface is very sensitive to scratches, pits, and material impurities. This process is typically used in decorative items, medical parts, optical parts, and high-end consumer electronics industries.
Type 6: Brushing
We usually carry out the specified direction of brushing according to your requirements. This process not only conceals our slight scratches but also retains the metallic texture and reduces mirror reflection.
If you have higher requirements for the brushing direction of the product, please inform us in advance.
Type 7: Electroplating
Electroplating is the process of depositing a metal layer on the surface of aluminum through an electrochemical reaction. Electroplated aluminum usually requires pre-treatment (such as zincate or chemical nickel plating) to ensure adhesion.
Commonly used coatings include: nickel, chromium, copper, silver and gold. If the product you are designing is a mating hole, plug-in component or precision structure, then you need to consider whether the coating tolerance affects the size of your product.
Type 8: PVD Coating
If you are designing aluminum CNC parts and considering PVD, there is one thing you need to keep in mind: Aluminum is usually not used directly as the base material for PVD.
The reason is that an oxide layer naturally forms on the aluminum surface, which will affect the adhesion stability of the PVD coating. To ensure that the coating does not fall off during long-term use, you usually need to add an intermediate layer treatment before PVD, such as chemical nickel plating or nickel electroplating system, to improve the adhesion and reliability.
Type 9: E-coating
If you are designing aluminum CNC parts and need a white or light-colored surface treatment, electrophoretic (E-coating) is usually a more stable option compared to anodizing.
Electrophoretic coating achieves color by forming a uniform paint film on the surface, making it easier to achieve white, light gray, or low-saturation colors.
Aluminum Finish Comparison (Anodizing vs Powder Coating vs E-Coating)
When you choose the manufacturing process for your product, you might be confused between anodized electroplating and powder coating. The following table helps you better understand the differences between them and how to make a choice. If you are unsure, you can also seek advice and assistance from us.
| Category | Anodizing | Powder Coating | E-Coating |
| Surface Appearance | Metallic finish, retains CNC texture | Fully coated, non-metallic appearance | Uniform functional coating |
| Color Capability | Limited (white/light colors difficult) | Full color range including white | Stable light colors (white/grey) |
| Surface Texture | Matte / semi-matte metallic feel | Coated texture with slight grain | Smooth and uniform coating feel |
| Thickness & Dimensional Impact | Medium (~5–25μm) | High (~60–120μm) | Low–medium (~15–35μm) |
| Electrical Conductivity | Insulating | Insulating | Insulating |
| Complex Geometry Coverage | Medium | Limited in deep cavities | Excellent (deep holes & internal surfaces) |
| Corrosion Resistance | Good | Excellent | Excellent |
| Wear Resistance | Good | Good | Medium |
| Cost Level | Medium | Medium | Medium–low |
| Typical Applications | CNC housings / consumer electronics | Industrial enclosures / outdoor parts | Complex housings / white or functional parts |
| Engineering Risks | Color variation / surface defect visibility | Tolerance impact / masking required | Limited metallic aesthetic |
How To Choose Aluminum Finish for CNC Machining
If you are designing CNC aluminum parts, surface treatment should not be decided at the very end of the design process. Instead, it should be considered together with the design in the initial stage, as it will directly affect the appearance, size, functionality and cost of the product.
1. Color Requirement
Color is usually the first filtering criterion. Since anodizing has significant limitations in light colors such as white.
If you need a metallic appearance, anodizing is usually the preferred choice. However, if you require white or light colors, e-coating or powder coating is generally more suitable.
2. Surface Texture
The surface texture will directly affect your users’ perception and the sophistication of the product. Different surface treatments will completely change the visual effect of the product, which entirely depends on your product positioning.
If you want to retain the CNC machining texture, anodizing or brushing is usually the right direction. When a fully covered and uniform surface is preferred, powder coating or e-coating becomes more suitable.
For a high-gloss or mirror-like finish, you would typically go with polishing or even PVD. And if you are aiming for a matte and more industrial feel, sand blasting is the most common option.
3.Functional Requirements
If conductivity or grounding is required → Avoid anodizing and powder coating (insulating layer)
If high wear resistance is needed → Use hard anodizing
If the structure is complex (deep holes/inner cavities) → Electrostatic coating provides better coverage
If high precision is required in combination → Avoid thick coatings (such as powder spraying)
4.Cost & Production
Different surface treatments will significantly affect the overall cost structure.
- Anodizing: The most cost-effective option, suitable for most CNC aluminum parts, and we have our own anodizing production line.
- Powder coating: Offers a wide range of color options, but the film layer is relatively thick.
- Electrophoretic coating: Suitable for complex structures and with relatively stable cost.
- PVD / Electroplating: Higher cost, suitable for high-end or functional product
Engineering Mistakes When Choosing Aluminum Finishes
When you choose to have products made by suppliers, many problems are not design-related but rather result from choosing the surface treatment too late.
- If you don’t choose to reserve the coating thickness, it will affect the assembly of your product.
- Misunderstanding that anodizing can be used for white.
- Ignoring the insulating layer leading to grounding failure (this is the most common mistake).
- Hoping that the surface treatment can reserve the grooves (we will provide you with suggestions and you don’t need to worry about this).
Therefore, we suggest that you contact us during the design stage. This will definitely be of great help to your choice.
FAQ
What is the main surface treatment for aluminum materials?
The most common surface treatment method for aluminum parts is sand blasting anodizing. This not only meets the aesthetic requirements of the product but also takes into account its cost-effectiveness.
Is it possible to combine different surface finishes on the same part?
Yes, multiple surface finishing processes can be combined on one part when required. Pre-treatments such as polishing, sand blasting, or bead blasting are often applied before anodizing, while PVD coating typically requires a prior plating layer as the base.
Is anodizing better than powder coating?
The cost-effectiveness of the anodizing is indeed the highest, but the anodizing also has some limitations, such as the choice of color.
Does anodizing affect tolerances?
Yes, we need to take tolerances into account when anodizing. If you’re unsure about the size of the tolerances, don’t worry. We have extensive experience with anodizing.
Which aluminum finish is most scratch resistant?
My suggestion is to perform hard anodizing. It enhances the wear resistance and hardness of the product.
Which finish is best for keyboard cases?
The aluminum keyboard case offers us a variety of surface treatments. The most common ones are sandblasted anodizing, plating and powder coating. Of course, we have now developed a special process independently. If you have any requirements, please feel free to contact us at any time.
Final Thoughts
We are a one-stop aluminum parts customization factory. Most of the surface treatments for aluminum materials can be completed within our factory.
If you are currently considering designing a product and are unsure about the choice of surface treatment, please feel free to contact us at any time.
