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Copper contamination of Iridite?

July 13, 2011

We recently performed tape lifts on some problematic Iridited Al 6061-T6 parts. The samples showed oxidized aluminum particles with Iridite coating. The aluminum/iridite particles did not show any other contaminants or unexpected elements. However, the tape lift samples also showed a large amount of extremely fine copper particles (tens of nanometer to sub micro in size), which are very unusual.

While the root cause of the Cu particles is still fluid, one thought would be the Cu coming from the baths. How feasible would this be? and/or would there be anything in particular to look for that would indict the bath chemistry vs an external cause?

Thanks!

Mike Beam
Materials Engineer - York, Pennsylvania, USA

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With or without copper contamination, if the chromate conversion coating is too thick it will shear with tape pulling (and with paint). That is why we preach to put the chromate on very thin for use under paint (and now tape).

Copper contamination will cause a light to no coat, and also cause to fail salt spray. But where is your copper coming from? It is not in the commercial chromating product you named. It most commonly comes from processing 2024 alloy, or dropping copper hooks in the solution. Deionized water running thru copper pipes/fittings will also pick up a "smidgen" of copper.

May I question whether you are using a good "mixed acid" deox? That will do more towards getting the copper off the surface than just plain nitric acid (or one of these new persulphate formulations.)

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

July 13, 2011