We hope to offer engineering type comments helpful to both those who design components from aluminum metal and those who are responsible for finishing these components. Often times, most engineering or design of parts takes place with little thought to the type of finish chosen. This can have significant impact for aluminum parts where anodizing is the finish of choice for decorative or performance reasons.

Alloys:

Machine companies like to use 2000 series aluminum because it cuts quickly, increasing their throughput. The high copper 2000 series like 2024 or 2011, however, are difficult for anodizing. They often have white spots and pits from the anodize process. If the finish of your parts is very important it is best to stay with easier alloys to anodize such as the 6000 series - 6061 or 6063 bar stock.

Racking:

One of the best things a designer can do for a machined part that will be hardcoated is to put a dedicated racking hole. This threaded hole will allow the finisher excellent contact and significantly reduce potential burning because of the higher electricity applied during the hardcoating process.

Design:

Sharp corners for anodized parts should be avoided. The anodic coating grows at a 90 degree angle to the base metal. The anodic coating is weak where it bends around sharp corners. Shouldered corners are helpful.

Application:

One of the most helpful decisions that can be made prior to processing is the degree of performance which the anodic coating must provide. An interior cabinet hardware piece and a canoe gunwale, both Mil Spec 8625 type II class 2, will have significantly different processing requirement. The degree of coating hardness, lightfastness, and corrosion resistance will be different. The finishers needs to know these requirements.