January 11, 2021

How to Anodize Aluminum

Anodizing aluminum parts can be an efficient way of adding enhanced mechanical properties to parts or improve their aesthetics. Many people don’t know how to anodize aluminum, even though the process is fairly simple. Read on to learn more about anodizing aluminum at home or in a production factory operation.

Why You Might Want to Anodize Aluminum

There are several good reasons to consider anodizing your aluminum parts. When anodizing aluminum, a layer of oxide is created and forms a layer on the aluminum’s surface. This layer is so thin that it doesn’t even materially impact the dimensions of precision machined parts. Because the oxide layer is harder than the aluminum, it protects the metal underneath it, making it scratch-resistant and increasing corrosion resistance.

The oxide layer is also rougher than the aluminum surface, making it possible to paint or dye the anodized aluminum. In fact, you can add any color you like to anodized aluminum parts. Coloring is accomplished either by using dyes during the anodizing process or by painting afterward. Dying is preferred, as it creates permanent coloration which means it won’t fade and can’t be scratched off.

Benefits of Anodizing Aluminum Parts

Anodizing aluminum parts provides many benefits, both in terms of aesthetics and the mechanics of the parts themselves.

On the visual side, the effects are quite impressive and the finish is permanent. It is wear-resistant so it will never scratch or fade and will never need a touch-up. Plus, it’s environmentally friendly.

On the mechanical side, the anodizing process makes the surface of the parts extremely durable. The oxide is extremely hard and provides superior abrasion and corrosion protection. The thermal insulation properties are also outstanding.

Overall, the process makes parts look better and more durable. Plus, the process is very affordable, even if you’re the hobbyist and the type of individual that will be going to do it yourself at home.

Materials Needed to Anodize Aluminum

The materials you’ll need to anodize are pretty basic and not too expensive. If you think you’ll be doing this somewhat regularly, it makes sense to set up a home anodizing station.

Here’s what you’ll need:

  • Sulfuric acid
  • Distilled water
  • Several tanks (containers) to hold the liquids
  • A cathode
  • Aluminum wire (titanium will also work)
  • Degreaser
  • Lye
  • Acid neutralizer
  • A power source
  • Dye (if you want a colored part)

You will also need a well-ventilated area to set up your anodizing station, as well as personal safety gear (eye protection, gloves, respirator, etc.).

In addition to the necessary materials above, you may also want to purchase some optional items to make your work easier. These include the following:

  • An agitator for the acid bath
  • Scotch-Brite pads for cleaning parts before anodizing
  • Ping pong balls (put in the tank to prevent acid mist)
  • Cheap tea kettle to heat dye
  • Fish tank heater to regulate tank temperature
  • Cooking thermometer for checking temperatures

How to Anodize Aluminum at Home

Below are the basic step-by-step instructions to follow for the at-home hobbyist to anodizing aluminum parts yourself. Please keep in mind that it does take time to master the process, and your materials may require some tweaks.

  1. Use the Scotch-Brite pad to clean the surface and remove any machining marks.
  2. Put on your safety equipment, including gloves.
  3. Use the degreaser to clean the part well, then rinse with the distilled water.
  4. Etch the part by dipping in a lye bath for 3-5 minutes. Use roughly 4 tablespoons of lye to 1 gallon of water.
  5. Remove from the lye bath and rinse with distilled water.
  6. Check for cleanliness by pouring water on the piece. If clean, the water should runoff. If the water beads on the surface, the part is not clean enough for anodizing.
  7. Rack the part by securing it to the aluminum (or titanium) wire. Ensure the connection is good, and don’t forget there will be an unanodized mark where the wire is in contact with the part.
  8. Create the bath by adding sulfuric acid to the distilled water in your anodizing container at a ratio of 1 part acid to 3 parts water. Note that anodizing is most successful when the bath temperature is 70 degrees Fahrenheit. Anything above 75 F or below 65 F won’t yield good results.
  9. Now everything goes in the tank. Add the cathode, making sure it won’t touch the part(s). Add the agitator. Suspend your parts in the tank, making sure they aren’t touching anything. Add the heater and thermometer. Add the ping pong balls to cover the surface.
  10. Make sure the temperature is 70 degrees before proceeding.
  11. Set up your power supply and connect the positive terminal to the wire attached to the part(s). The negative side is attached to the cathode. Now things can get touchy.
  12. The amperage is set based on the total surface area being anodized. For a good, hard surface, use 0.03 amps per square inch, and for a softer surface that will take dye better, use 0.02 amps per square inch.
  13. Start at 16 volts. You can find all sorts of online calculators, but a home setup starting at 16 volts should get you pretty close. Keep an eye on the tank temperature as the process goes along. The temperature can increase when the process is underway.
  14. While the anodizing process is going on, heat your dyes. For most colors, 140° F works best for most colors, but some work better at cooler temperatures. You’ll have to experiment with your brands and colors.
  15. Prepare one tank of distilled water and another with your acid neutralizer.
  16. Turn off the power and remove your parts from the anodizing tank. Dip first in the distilled water for 10-15 seconds, then rinse in the acid neutralizer tank for 5 minutes. Rinse a second time in the distilled water and dunk the parts in the dye. They should immediately begin to take the color, but be sure to leave the parts in the dye for 10-15 minutes, depending on how deep you want the color to be.
  17. After finishing with the dye, you want to boil the parts for 15 minutes. Boiling hardens and seals the dye.

Anodizing at home is doable for the layperson, but many other metal fabrication processes like forging, stamping, and extrusion require a professional manufacturer. If you require custom metal products and processes, contact The Federal Group USA today.

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