Curated with aloha by
Ted Mooney, P.E. RET
The authoritative public forum
for Metal Finishing 1989-2025
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Chem Film on Aluminum is Cloudy
Quickstart:
Aluminum is often 'chromate conversion coated' as a corrosion resistant final finish or as a pretreatment for painting or powder coating. The process actually involves many steps, usually including alkaline cleaning, etching, deox/desmut, the chromate conversion step per se, and water rinses between each step.
MIL-C-5541 / MIL-DTL-5541 / MIL PRF-5541 is the most commonly cited spec. "Alodine" and "Iridite" are trade names. "Chem film" is a slang term for the process.
Q. We have an aluminum enclosure made from 6061-T6511 material. This enclosure is machined complete and sent out for chem film per MIL-DTL-5541, Ty 2 Class 3. When done, these parts always have a slightly cloudy appearance that our customer ultimately rejects. Out vendors say there is nothing they can do because of the process. Any suggestions?
Scott StaplesQuality Manager - Bloomington
March 3, 2025
A. Hi Scott. It looks like you were going to send us a pic but forgot to add the attachment? Pics might help you get opinions about the parts you received.
Contract disputes can be minimized by all parties agreeing on a spec. Perhaps your customer as well as you and your vendor can agree that Mil-DTL-5541 will be the ruling specification?
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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