Faded aluminium anodising

Hi all,
I have an aluminium trike which I built from a kit. Before I assembled
the tubes, I had them anodised bright red
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.About 18 months on, one of the tubes has changed colour considerably.
It is now a dull pink and looks completely different to the other
tubes. I suspect that the tube may not have been sealed properly after
being dyed? Is there any way that the colour can be restored? Any form
of heat treatment is out because the trike is bonded, and anything
over 60 degrees or so will break down the glue. If nothing can be done
to restore the anondising, how easy would it be to paint? Would I have
to remove the anondising first to get the paint to apply properly, or
are primers available that would adhere to the anondising?
many thanks
dan.
Reply to
Daniel Towner
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Bad news. I found out years ago that red is the most unstable dye. The color in anodizing is simply dyes sealed into the pores in the metal. UV light, even from fluorescent lights will break down all red dyes over time. There may be some red dyes that are more resistant to this than others, but I think there are all degraded by exposure to UV. Possibly some sort of clear coating that has UV absorbing properties would have helped slow the loss of color. Now, you have few choices. Paint should stick to the anodized surface, maybe even better than bare aluminum. A primer might be needed.
Jon
Reply to
Jon Elson
It all depends on the dyeused too. A good sealer and dye will resist fading for a substantial length of time. But even the best dye unsealed will fad quickly. I anodized a couple plugs and didn't seal them because I didn't like the color and they faded in a couple weeks.
Russ Wizinsky
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Reply to
Russ Wizinsky - ProfessorWiz
The dyes used are organic and will fade with time and UV exposure. When we did the 1000 hour salt spray test(which also involved hard UV exposure from arc lamps), the "black" dye we used on motorhome trim faded away in less than 50 hours, the test plate itself disappeared in less than 200, didn't last much longer than the bare aluminum control. Red dye is ephemeral at best, I'd never use it on anything that would be continually exposed to sunlight.
I'd normally put in a plug for powder-coating here, but your finished item is glued and the heat needed for a cure will definitely make it fall apart. I'd suggest contacting an auto body and paint supply place and see what they recommend. Car finishes are some of the toughest coatings to be had, assuming you've got spraying equipment to apply them. A two-part epoxy paint might also be worth locking at. You're probably going to have to sand off your anodizing to get the paint to stick properly. We never powder-coated over anodizing, the treatment was to do a chromate conversion coating first, then powder-coat after rinsing and drying.
Stan
Reply to
Stan Schaefer
Anodizing makes a great paint base, one of the major choice for a lot of aerospace components. Since you can't reanodize, clean the surface with MEK and use an epoxy prime as a base.
Ed Angell
Reply to
Ed Angell
You can re anodize by stripping the old stuff off first. Check
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they've got stripper and more info.
Russ Wizinsky
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Reply to
Russ Wizinsky - ProfessorWiz

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