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The X-Tiles Video Series: Anodized Aluminum and More

Watch part 5 of our video series, the X-Tiles, to help you distinguish between the most common CNC machining post-finishing, including standard and hardcoat anodize, E-Nickel plating, and chem chromate conversion coatings.

By Greg Paulsen

Know Your Anodize: Type II vs. Type III

Anodizing is one of the most practical means of providing long term corrosion resistance, additional durability, and a permanent nonconductive surface finish to metals. Anodizing works best for metals like aluminum, titanium, and magnesium. The most common anodizing process is done per MIL-A-8625 standards. Typically this finish is applied to CNC machined parts or sheet metal components after fabrication, but before operations like part marking or adding inserts. Type II, Class 1, anodizing is commonly found in clear, black, or colored varieties. In the video, you can see examples of Type II and how it affects the surface finish. If the part requires higher wear resistance, Type III, Class 1, anodizing may be the best option due to an increased thickness of the oxide layer—acting as a protective shell for the part.

Anodizing vs. Metal Plating

Anodizing is not the only option to ruggedize or enhance the properties of CNC machined metal parts. In this video, anodizing is compared against metal plating—specifically, electroless nickel plating. Also known as E-Nickel Plating, this process produces a uniform coating of nickel-phosphorus through a chemical dip bath. Metal plating utilizes the conductivity of the metal to attract and bond a different metal to a part's surface. Examples of metal plating are nickel, zinc, tin, gold, and silver. Like anodizing, nickel plating can give a part excellent corrosion resistance as well as high wear resistance. Beyond aluminum, nickel plating is popular for materials that can rust, like steels, or softer metals to prevent wear marks. Precious metal plating, like gold, can enhance external conductivity and prevent oxidation. Gold plating is typically applied to copper CNC machined or sheet metal parts. It is important to understand that plated parts maintain electrical conductivity where anodized components are non-conductive.

Anodizing vs. Chromate Conversion Coating

Chemical chromate conversion coating, sometimes called chem film, adds a protective coating that is electrically conductive. It is often applied to materials like Aluminum 6061, 7050, or 7075 as a preparation for other surface treatments. It is not uncommon to have multiple finishes, starting with a clear or gold anodize then moving to powder coat, metal plating, anodize, etc. Chem film is most popular with electromechanical assemblies because it allows the part to be a ground plane while preventing oxidation on the contact surfaces. Chromate conversion is not wear-resistant like anodize, which should be a consideration depending on the lifetime use of the part.

About the X-Tiles

The X-Tile series takes a show and tell approach to manufacturing outcomes using various platforms, materials, technologies, and finishes. You can check out the other posts in the series here:

What is an X-Tile? We took the ‘X’ from our Xometry logo and designed a custom part that is about 1.5 inches square. It has flats as well as angled surfaces. The tile is producible in multiple manufacturing processes and acts as a good comparison part for material finishes and cosmetic features like layers.

Greg Paulsen

They call me the Director of Application Engineering at Xometry. This means I not only get to produce great design-for-manufacturing content, but also consult on a variety of custom manufacturing projects using CNC machining, additive manufacturing, sheet metal, urethane casting, and injection molding. If you have a question, I'm your guy.