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Anodized aluminum is turning yellow

What can cause architectural anodized (Class 2)clear aluminum to yellow . Extrusions that have been exposed to outside for 1-2 years.

1. Could it be a sealing problem;
2. Cleaning compounds used for maintenance;
3. Contaminants in rinses or seal bath;
4. Other. Also, have you dealt with this type of problem in your experience and what was the solution or cause?

Thanks,

Catharine Bryla
sales rep - Mississauga, Ontario, Canada
2003

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Your problem seems arisen from poor sealing and/or inadequate thickness of anodic oxide film. Poor sealing may be a result of contaminants in the sealing bath or insufficient temperature /ph / immersion time.

Also avoid chemicals to clean the anodized surface. The anodized surface can be cleaned by soap solution. No strong alkalis / no acids / no mechanical brushing for cleaning.

Tim
Aluminum Extrusion & Finishing - Istanbul, Turkey
2003