Anodizing

Aluminum parts are light weight, relatively strong, and affordable to manufacture. As a result, it is one of the most common materials to use when designing a part. An often-overlooked consideration for aluminum, however, its oxidation performance. We worry about steel parts rusting, but rarely do aluminum parts get the same attention. This is where today’s topic, anodizing, comes into play.

What is Anodizing:

Anodizing is the process of forming a controlled and purposeful oxide layer on a non-ferrous part. While such a layer can be produced on titanium, magnesium, zinc and other metals, it is most common on aluminum. This is both because aluminum parts are more common, but also because the properties of aluminum-oxide formed by anodizing are formidable. Applying an oxide layer to aluminum is also much easier than for those other metals.

How is Anodizing Performed:

Every anodizing process has its own formula, however they all follow a similar outline. The process typically begins with cleaning the part of any contaminants or existing oxide layers. Often a maroon Scotch Brite pad and acetone is enough for this step, with a water rinse afterwards. Then an acid etch is applied to remove any residual layers, activate the surface and prepare it to grow the coating. From there the part is rinsed again and placed in another acid bath. This time a voltage is applied which causes the surface of the part to react with the acid, growing an oxide layer.

Once a sufficient oxide layer is grown, it is critical to stop the process with a neutralizer, or the part will continue to oxidize. This is where the core process ends, and additional steps can be taken to add colorants or additives to impact usability. A common practice is dunking the freshly neutralized part in boiling dye, adding a durable, ultra-thin coating of color to the part. Since the oxide layer is absorbing the dye, it does not flake or add to the component dimension. Some formulas even apply wear additives.

Why Anodize Parts:

Aluminum-Oxide is an incredibly hard material, most often used in manufacturing abrasives. By applying this ultra-hard coating to the surface of a part, the wear performance increases dramatically. Normally aluminum is too soft for usage in mechanical assemblies, but through anodizing, the surface can be toughened enough to be used where steel would otherwise be required.

Anodizing also has the benefit of producing a slightly porous surface, allowing adhesives and paint to stick to aluminum parts. Due to the low reactivity of Aluminum, it is often difficult to use paints/adhesives without extensive prep. An anodized surface, however, can be painted like steel.

It is important to note that the electro-chemical reaction happening is causing the part to oxidize in a controlled manner. This is unlike say nickel or chrome plating where the bath is depositing material onto the part. This means that dimensions generally don’t change after anodizing. This allows anodizing to be the last step, easing manufacturing.

The final reason to anodize parts is for corrosion protection and aesthetics. By applying the color directly to the part, painting steps can be avoided. In addition, since the coating is an oxide layer, it prevents additional oxidation. This can be a huge help in assemblies where environmental conditions or galvanic corrosion would otherwise damage the part.

Conclusion:

As you can see, anodizing is a pretty amazing process. It brings with it so many advantages, all with such a small cost, allowing a designer to take full advantage of the aluminum benefits. We generally recommend all parts get anodized, simply because it adds so much functionality for such a small effort. If you’re designing a part, and unsure what coatings to apply, contact us today! We have the expertise to recommend the perfect coating for every part. Also, keep an eye on the blog, we’re going to be talking about even more coatings in the near future!

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