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White scratches on black anodized pieces

2007

Hi,
I'm having problems with white scratches (not spots) in some 6082 black anodized wheel rims.
Where anodizing at 1 A/dm2 at 10 g/l Al.Bath temperature 18-19 °C. Air agitation
The wheel rims are polished before the bath. and after the process, you can observe those white - grey scratches over the rim. They are located at a sharpened edge so I thought it was a polishing problem, but they're still there after repolishing and rounding the edges as possible..
I don't know what else to do. The rest of the anodic coat seems oK, but those sharpened edges look awful.

I'm having the same problem with some extruded profile for heatsinks (6063),at the edges you can observe that it's not black

please help me

Sergi Fernández
desperate - Spain

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I do not fully understand your definition of the problem. Be aware that on a sharpened edge, that the anodic film goes half into the metal and half on top. If the sharpened edge is not uniformly of the same thickness, then in some places you are completely converting the base aluminum into aluminum oxide, and then in thicker places you are not completely cutting through.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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Sergi,

Sorry, being late in replying.
Is it possible to attach a photograph of the defect?

Thanks & regards,
Basu

Srimay Basu
Dubal - DUBAL, U.A.E.
2007

Ed. note: Please do so by mailing the photo to mooney@finishing.com with a note that it's for letter no. 44280. Thanks.

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Mr Basu,

Finally I've send the photo.
 

This is the same defect but in a blue anodized heatsink. I hope that this is usefull for finding the answer to this defect.

Thanks

Sergi Fernández
- Spain
2007

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Try to clean the edges before anodizing, it looks like rest of polishing process. Test with parts pulish and other not. Maybe the overheat of the process affect the material.

regards,

Alex Delgado
- Spain
2007