Summary for cloudy chem film Discussion
Chem film on aluminum is cloudy is the issue raised in this thread, which points to chromate conversion coating as a corrosion-resistant finish or pretreatment for paint or powder coating. The excerpt does not include the full Q&A, but it does note that the process usually involves several steps: alkaline cleaning, etching, deox/desmut, the chromate conversion step itself, and water rinses between each stage. It also references MIL-C-5541 / MIL-DTL-5541 / MIL-PRF-5541 as the governing specifications. Because the visible text is only the thread header and process note, no specific diagnosis or remedy is shown in the excerpt. The practical takeaway is that cloudiness in chem film is often tied to process control across the cleaning, etching, desmutting, conversion, and rinsing sequence, and the relevant specification should be checked for acceptance criteria.
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 MIL-DTL-5541
[⇦ this spec on DLA] is the most commonly cited spec. “Alodine” and “Iridite” are proprietary trade names of the suppliers of the process chemistry. In the USA “Chem film” is an often used 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 Staples
Quality 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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