The authoritative public forum
  for Metal Finishing since 1989
-----

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 Sieloff
Quality 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
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.