After precision CNC machining, applying proper surface treatments can enhance appearance, protect from corrosion, improve wear resistance, or provide aesthetic appeal. In this post, we explore common finishes for aluminum CNC parts and how to choose among them.

Why Surface Treatment Matters

Machined aluminum often has tool marks and slight surface roughness (e.g. Ra 0.3). Surface finishing:

• hides imperfections

• improves corrosion resistance

• enhances visual appearance

• provides additional hardness or wear resistance

Common Aluminum Finishes

1. Anodizing
   A controlled oxide layer is grown on the aluminum surface. It provides corrosion resistance, electrical insulation, and allows coloring. Hard anodizing (Type III) gives better wear resistance.

2. Powder Coating / Painting
   Offers a thick, durable colored coating. Good for visual appeal and protection against environmental damage.

3. Bead Blasting / Sand Blasting
   A mechanical process that gives a matte or uniform finish by propelling fine beads/sand. Often used prior to painting or anodizing.

4. Electropolishing
   A chemical method that smooths the micro peaks, reduces surface roughness, and increases corrosion resistance.

5. Passivation
   Chemical treatments (e.g. chromate conversion coatings) that enhance corrosion resistance, often used in conjunction with anodizing.

6. Polishing / Buffing
   Mechanical polishing leads to smooth, mirror-like finishes—used in aesthetic or precision components.

7. Hard Coatings / PVD / DLC
   Advanced coatings like physical vapor deposition (PVD) or diamond-like carbon (DLC) offer hardness, wear resistance, and low friction. More costly but useful in demanding environments.

Matching Finish to Application

• Aerospace & defense: anodizing, hard coatings

• Consumer electronics: anodized color or brushed finish

• Corrosive environments: anodized + sealing, or specialized coatings

• Wear surfaces: hard coatings or PVD

Design & Process Tips

• Consider post-machining allowance: leave a small extra layer so final finishing doesn’t remove functional features.

• Avoid sharp corners that trap media during blasting.

• Ensure uniform thickness where coatings are applied.

• Communicate required finish spec (e.g. color code, roughness, coating thickness) explicitly in drawings or notes.

Inspection of Finished Parts

• Thickness of coating: check by non-destructive methods (e.g. eddy current)

• Adhesion: use tape tests or scratch tests

• Corrosion test: salt spray or humidity exposure

• Color and gloss consistency

By selecting appropriate surface treatments and integrating them into your machining workflow, you can elevate the performance and aesthetics of your aluminum machined parts.