
Curated with aloha by
Ted Mooney, P.E. RET

The authoritative public forum
for Metal Finishing 1989-2025

-----
Cured application of Alodine 1200 passivate new coat of 1000
Paint adhesion is a problem on aerospace aluminum after a combination pretreatment in Alodine 1200 followed by a treatment in Alodine 1000. The paint is an epoxy primer with a urethane topcoat. One of the paint supervisors is guessing that the dried 1200 coating is passivating the newly laid 1000 and preventing adhesion of the epoxy primer. I'm not a chemist by trade so I'm hoping some folks here have a clue.
TIA,
Bruce SieloffQuality Engineer - Kent, Washington, USA
2003
Although I have a background in chemistry I also am not familiar as these two chemicals are proprietary. Their exact composition is not known that I can only make inference based on the technical literatures the manufacturer provides.
Alodine 1200 is relatively thicker than Alodine 1000; the latter is the preferred choice for coating that require minimum electrical resistance. The former is the usual choice for pretreatment prior to paint coating. I found it very unusual to apply a thicker conversion treatment only to dissolve it later and recoat the parts with a thinner coat. Have you tried applying paint with only Alodine 1200 on?
Ciraco Dipaloloco- Toronto
2004
2004
"a combination pretreatment in Alodine 1200 followed by a treatment in Alodine 1000" doesn't sound like an approved aerospace process. Probably also violates MIL-C-5541E, which prohibits mixing different chem film solutions.
"guessing that the dried 1200 coating is passivating the newly laid 1000" -- guessing indeed. Was the Alodine® 1200 coating accidentally baked, and someone guessed that Alodine® 1000 would heal the cracks?
As a Quality Engineer, you should stop all the guessing and ad hoc chemistry experiments. Return the process to approved procedures, which probably includes drying the fresh Alodine® 1200 coating for 24 hours at 70-90 F before priming.
Ken Vlach [deceased]- Goleta, California

Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
Q, A, or Comment on THIS thread -or- Start a NEW Thread