How to Select a Finish for CNC Machined Aluminum

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CNC machining produces precise and durable aluminum parts, but the raw milled surface often requires a finishing process to meet functional, aesthetic, and applicationspecific demands. Selecting the right finish is a critical step that can significantly enhance the value, performance, and longevity of your components. For businesses in industries from aerospace to consumer electronics, making an informed choice is paramount.


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Key Considerations for Selection

Before choosing a finish, define your part's requirements:

1. Corrosion Resistance: Will the part be exposed to moisture, chemicals, or harsh environments? Anodizing is a top choice for creating a hard, nonconductive oxide layer that drastically improves aluminum's natural corrosion resistance.
2. Aesthetics & Branding: Is the part's appearance important? Options range from media blasting for a uniform matte finish to bright dipping for a highly reflective, mirrorlike surface. Anodizing also allows for a wide spectrum of color choices.
3. Wear Resistance & Hardness: Will the part experience friction or abrasion? Hardcoat anodizing creates an extremely hard surface, rivaling tool steel, making it ideal for gears, pistons, and highwear applications.

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4. Dimensional Stability: Some finishes, like powder coating, add a significant layer of thickness. If your part has tight tolerances, an electropolish or a thin, Type II anodize might be preferable as they add minimal dimension.
5. Electrical Conductivity: A raw machined surface is conductive. If this is necessary, a conductive chemical film like Alodine® (chromate conversion coating) is a good option. Note that anodizing is nonconductive.

Popular Finishing Options for Aluminum



Anodizing (Type II & Type III): The most common finish. Type II offers good corrosion resistance and color. Type III (Hardcoat) provides superior wear and corrosion resistance.
Chemical Film / Chromate Conversion: A thin, conductive coating that provides excellent corrosion resistance and serves as a good primer for paint. Common in aerospace and military applications.
Powder Coating: A thick, durable polymer coating applied electrostatically and cured under heat. It offers excellent color options and protection against impact and corrosion.
Media Blasting: Uses fine abrasive media to create a uniform, satinlike matte surface, excellent for aesthetics and preparing a surface for other finishes.
Electropolishing: An electrochemical process that removes a thin layer of surface material, deburring the part and providing a smooth, bright, and clean finish.

Partner with a Pro for Optimal Results

The optimal finish balances performance, cost, and lead time. As a professional onestop CNC machining service, we provide expert guidance to help you navigate these choices. By selecting the ideal finish for your aluminum parts, you ensure they meet the highest standards of quality and reliability, ultimately protecting your investment and driving the success of your products. Contact us today to discuss your project requirements.