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Chemical Conversion Coatings on Aluminum
(to provide context, hopefully helping readers more quickly understand the Q&A's)
Chromate conversion coatings, sometimes called "chemical conversion coatings" or "chem-film" are a corrosion resistant coating applied to aluminum parts. The most common specification for the coatings is MIL-C-5541 / MIL-DTL-5541 / MIL-PRF-5541.
Alodine is a Henkel trade name for their popular line of chromate conversion coatings for aluminum; Iridite is MacDermid's trade name for theirs.
Q. Hello,
Is it possible to perform Chemical Conversion on parts with blind female 0-80 UNF Threads, without making the thread unusable? (due to fluid locking & hardening inside the thread drill / or due to the thickness of plating - 0-80 is very small)
or should I mask the thread? (but then the area will be exposed for corrosion).
The aluminum is 6061.
The Chemical Conversion is type I (Alodine 1200s)
Thank you.
- Haifa, Israel
December 12, 2021
A. Hi Alex. I wouldn't expect the thickness to be a problem, but getting the processing liquids in and out probably will be. A vibratory plating barrel (they're not really 'barrels', they look more like a sieve) might work. If volumes are very small you might see if an [on eBay or Amazon] can help with getting the solutions in and out.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 2021
A. Alex
Yes, you can conversion coat 0-80 threads. A while back, we were processing microwave parts with up to ~96 of them. They would take a considerable amount of time to process/rinse/dry. Price the job accordingly.
- Green Mountain Falls, Colorado
December 16, 2021
A. In addition to the two above, in all chemical metal finishing processes with blind holes, it is important to go up/down/in/out three times in all tanks: cleaners and rinses. Fill the holes, drain them, fill them again, drain them, three times completely in and out.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
December 16, 2021
December 17, 2021
A. Alex,
I agree with Ted, the process wouldn't make the threads unusable, but the challenge is getting the solution in and out to blind thread hole, so you will need some agitation or rotation to make sure the solution can get in and out.
Mark Battles
Plymouth, Minnesota
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