At Reata Engineering, our quality process encompasses every manufacturing stage, from design to product fulfillment.
After we manufacture, assemble, and test customers’ parts, we often send them out for plating, a finishing service we subcontract to trusted vendors. We closely manage these vendor relationships to ensure that our customers get optimal results.
When finishing is required, it’s our responsibility to help customers choose the proper coating method for their parts. To that end, we’re launching an in-depth series on the best plating techniques for specific materials.
In this first installment, we examine common coatings for aluminum parts.
Common Aluminum Plating Methods
The two most common coatings for aluminum are chem film and anodize.
Chem film coating
Also known as chromate conversion coating or Alodine®, chem film is a protective chemical conversion coating for aluminum parts. This plating method offers excellent corrosion resistance and paint adherence.
Chem film coating is broken down into two types:
- Type 1, or hexavalent (can be yellowish or clear)
- Type 2 (clear)
Type 1 chem film contains hexavalent chromium, which is toxic and, therefore, not compliant with Restriction of Hazardous Substances (RoHS) standards. For this reason, only Type 2 chem film is widely used today.
Chem film is also divided into two classes according to the degree of corrosion protection provided:
- Class 1A: A thicker coating that provides the ultimate corrosion protection, whether painted or unpainted
- Class 3: A thinner coating that provides corrosion protection in applications requiring low electrical resistance
Anodize is an electrochemical plating method that creates a durable, non-conductive finish. During the anodizing process, parts are placed in an electrolyte bath through which an electric current passes. The parts’ aluminum substrate reacts with the current to form a protective anodic oxide coating.
Anodized parts are non-conductive, corrosion-resistant, and durable. Available in a wide range of colors, anodize provides a beautiful aesthetic appearance.
Anodize is divided into three primary types according to coating thickness:
- Type 1 (decorative, thinnest)
- Type 2 (cosmetic, medium thick)
- Type 3 (hard, thickest)
It’s important to note that anodize both penetrates and builds onto the surface of a part, creating extra thickness that must be factored into tolerance calculations. With Type 3 anodize, in particular, tight tolerances can be challenging to maintain.
Selecting the Right Aluminum Plating Method for Your Part
So, which aluminum plating method is best for your part?
Interestingly, you don’t have to make an either/or choice. Many parts, such as the one pictured in this blog, have features that have been plated using both methods, which may be necessary to ensure that certain features are conductive, for example.
Here are some factors to consider when selecting an aluminum plating method(s):
Anodizing requires a higher level of technical skill than chem film coating and is, therefore, more expensive. When color and conductivity aren’t important factors, chem film is the likely best choice.
Anodize is available in virtually any color, though color variation can be an issue, so it’s important to follow best practices for achieving color consistency. Either plating method provides an excellent base for paint.
If your part—or a certain feature—must be electrically conductive, chem film coating is the only viable option of the two.
Chem film coating is a foolproof aluminum plating option for tight tolerance parts because it is a highly predictable process that adds minimal buildup to a part’s surface. If, however, you prefer anodize, we can work with you to adjust your tolerances during precision machining to account for anodize buildup.
At Reata Engineering, we go the extra mile to ensure your parts receive the optimal plating treatment, taking the time to understand a part’s end use and matching you with the appropriate vendor in our extensive network.
If you’re looking for a precision manufacturing partner who offers excellence from start to finish, we’re here for you. Request a quote today!