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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Severe flaking and corrosion on powder coated aluminium profile

2003

I have in front of me some powder coated aluminium profiles with severe flaking of powder profile in connection with water staining and corrosion (formation of corrosion product) One side of the profile has been mounted with cement, an elastic sealing compound was found on another side. There was no coating under the sealant - possibly a repair.

The profile surface seems very little etched. Supposedly a chromium-free conversion coating using Zr, F, P has been carried out, but I find little above noise level when scanning the surface. The powder coating thickness varies from next to nothing up to 80 microns.

Does someone have experiences with adhesion problems involving insufficient (?) etching. Has someone experiences with the corrosion resistance of chromate free pretreatment/ powder coating in cement?

Sabine Hofmann
support to aluminium casthouses and extruders - Karmoy, Rogaland, Norway

The whole profile should be pretreated and the thickness of the powder should not be next to nothing.

Remember that "You can't control what you don't measure". Although it may be very good to go chrome-free, if the alternative is an unmeasurable "supposedly a chromium-free conversion coating using Zr, F, P", you are nowhere. The consequence of being unable to measure is "severe flaking , , , and corrosion", and that's not what anyone could possibly call progress.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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