Metal finishing Q&As since 1989

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Colorfastness of dyed aluminum coatings

We are currently anodizing aluminum 2011-T3 parts to create red and black colored surface finishes for a customer. The customer has inquired if there is anything that can be done to reduce the amount of fading due to UV exposure, sunlight. The parts are anodized in accordance with MIL-A-8625 / MIL-PRF-8625 [on DLA], type II.

Steven Moehling
- Carpentersville, Illinois, USA

In general you can reduce the amount of fading observed by saturation dyeing the part - increase the oxide thickness as much as is acceptable to the customer, then use extended dyeing times, perhaps increasing the dye concentration as well. The object here is to get as much dyestuff in the oxide pore as possible. Make sure your seal is not just adequate but very good - use the acid dissolution test, not just dye stain. An obvious thing to check is to make sure you are using dyes that have the capability of good lightfastness - architectural or exterior quality dyes with a lightfastness rating of 8 or 8+ will provide good results.

Sjon Westre
- Minden, Nevada