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topic 271

Anodize flakes off only if done during summer


(1996)

Summer is coming and our anodize will start to flake and rub off after the parts are heated to 300 degree F. for one hour. The heat is needed to cure glue, etc. This was happened for the past three summers.

Many hours have been spent trying to solve this problem with no luck. This problem is seen with 2024 only. We anodize 2024 and 6061 only at this time. Our process is clean, etch, desmut, anodize, dye, and seal. This is type 2 anodize. The anodize is .0003 to .0005 inch thick, and we seal in nickel acetate. Any thoughts on this problem will be appreciated.

Thank You

Dennis Zdanowitz
- Michigan


probert book
Aluminum How-To

by Robert Probert
$89 New
The Chromating - Anodizing - Hardcoating Handbook





Surface Treatment & Finishing of Aluminium and Its Alloys
Wernick, Pinner & Sheasby

(1996)

Dennis,

Some thoughts on your problem:

1. I'm surprised you only have a problem in the summertime, I'd think a well sealed relatively thick coating would be prone to crazing at 300F any time (crazing might lead to subsequent flaking).

2. If memory serves me copper is the main alloying element in 2024 while silicon is in 6061. Perhaps they etch somewhat differently giving different surface topographies which might affect anodic film, and glue adhesion.

3. Are you sure it's the anodic coating that's flaking off and not only the glue.

4. I'm not sure it would be practical in your process, but you might look at the heat up rate and cool down rates. That is try to avoid severe thermal shock, bring up to 300 F gradually and cool down to say 100 F slowly.

Good luck,

Paul Stransky
- Putnam, Connecticut


safranek book
Properties of Electrodeposited Metals and Alloys

Safranek

November 15, 2008

Hi, gentlemen. It is true that the coefficient of expansion of the anodizing is much less than that of aluminum -- see Safranek for the numbers and more info =>

But I have Calphalon hard anodized frying pans where the anodizing would be far thicker than your numbers and, as a matter of practicality, it is both rugged and totally carefree temperature-wise -- as we put in on the stovetop (gas range) with no particular attention to heat up / cool down cycles at all, and has a lifetime guarantee to 500 deg F in the oven.

I don't know what grade of aluminum they use, but it's very true than 2024 is far more problematic than 6061.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



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