Black Aluminum Finish

Q. I am a tool engineer for a company that makes controls and timing devices. I am responsible for the finishing department. I want to make a cast aluminum part corrosion resistant. I have looked for information on anodizing in my various technical manuals and handbooks, but cannot find a complete description of this process. Can you help me with this information? Can this process be accomplished “in house” on a small scale? Can a black finish be accomplished? If so, what chemicals and processing steps must be followed?

I also want to know about any organic coating process that you would recommend that may be equal to or better than the anodizing finishing process for aluminum. T.T.

 

A. The process in question, anodizing, is an inorganic finishing process for aluminum. This process, which consists of several steps including cleaning, deoxidizing, treating and their associated rinses, can be accomplished on a small scale in your plant. In addition to providing corrosion resistance to aluminum, it is an excellent pretreatment for paint. Furthermore, it can be applied as a black finish.

But remember, you can’t cobble together an aluminum pretreatment system by yourself. Instead, I recommend you contact a supplier of anodizing chemicals and use the chemicals in accordance with his instructions. Suppliers of anodizing chemicals and equipment are listed on pages 220 and 221 of the 2007 PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE (www.pfonline.com/suppliers.html).

I do not intend to enter the controversy about inorganic vs. organic finishes for aluminum concerning the relative degree of corrosion protection they provide. Black inorganic coating are available. However, black organic coatings have always been available. These coatings are based on acrylic, epoxy, polyester, polyurethane and vinyl resins, which will provide a high degree of corrosion protection to properly pretreated aluminum surfaces.