Letter 15018

Hard Coat Anodize - Chipping/Flaking  

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We are using a hard coat anodize to protect an automotive part made from 6262 extruded. Should the anodizing chip or flake off during normal handling within the production process? Can you provide me a technical reference to support the conclusion?

Ken Tharp
- St. Louis, MO

I don't think you really need a technical reference that says hard coating should not flake off, Ken :-)

It's a given. If the hard coating flaked off my Calphalon pans I'd be at the store demanding my money back.

But you need to check that the part is specified to have generous radiuses on edges and corners because it is well known that hard coat with chip off of corners. Good luck.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

The mil spec that most hardcoat is done to, AMS-A-8625 [link is to spec at TechStreet] or Mil-A-8625 [link is to spec at TechStreet] tells you that any sharp edges or corners should be radiused or the coating may flake.

David A. Kraft Anacote Corporation Long Island City, NY

Ken,

It is not normal for the hardcoat to be chipping/flaking off, unless you are bending these parts after coating. When I have seen this problem, it normally is caused by the part getting too hot in the anodizing tank. Sorry I can't quote any technical reference, all I have is my experience (15 yrs). But if you are looking for anodizing reference books, they are available on this site.

Marc Green anodizer - Boise, Idaho

This is unlikely, but this happened to parts we processed long ago. It seems that an employee "discovered" that a dip in the nitric deoxidizer promoted better black dying. Naturally, the same guy figured out the if some was good more was better. Our customers were discovering that the finish cracked and compressed when they assembled the parts, and, somewhat later, that they were not retaining their color. By the time we got wind of the problem several customers had experienced problems. There may be short times during a production day when the dye needs an add or the pH is off that a short dip in nitric is a temporary fix. But that is not good practice, and we now test the lightfastness of the dye every day. Again, it is unlikely, but maybe worth looking at.

Peter Faxon
- Oxnard, CA

We currently recieved some parts back from our anodizer where the anodize is chipping and flaking off. The areas where the it's most apparent are on and around the edges of the parts. We have not seen this before. Is this normal? The material is 6061 and the anodize is black type III.

Dave Moskal
- Loveland, CO, USA

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