Summary for iridite 14-2 on 2024 Discussion
Iridite 14-2 on 2024 aluminum is the focus keyphrase here, and the thread centers on why 2024 panels are giving much worse chromate conversion results than other alloys. Zander Naes says the differences are drastic and repeatable across batches of 2024. F DiGiovanni asks whether the prep cycle removes excess copper from the surface, suggesting surface condition may be part of the problem. Willie Alexander advises comparing a mechanically cleaned panel against a normally prepped one to isolate the cause, and notes that in past work Iridite 14 performed best at the high end of the pH range, while also warning not to alkaline etch the panels. In a later follow-up, Steven Sanchez says they verify pH with a meter and 1.68 buffer, but still see an accelerated loose coating on 2024; he adds that they use an iron/nitric deoxidizer and that it is their first time using that type of deoxidizer.
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.
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“Surface properties of Conversion Coated Aluminum”
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Q. Hello,
We have recently been having trouble with our Iridite 14-2 tank. Long story short, our Iridite bath was not coating properly. After some troubleshooting, we managed to get customer parts (mostly 6061 and 7075) and 6061 panels to come out as expected, but 2024 panels are coming out very dark and with a powdery coating. I haven’t been able to run a 2024 panel without this powdery coating, despite lowering temperature, increasing pH, and lowering immersion times.
Our 6061 panels look great with immersion times ranging from 1 minute to 5 minutes. 2024, on the other hand, looks dark and powdery after only 1 minute immersion time. Most of the panel looks to have a light coating, but the edges are very dark and powdery. Increasing the immersion time provides a better coating on most of the panel, but the edges remain powdery (powdery coating does not seem to worsen significantly with this increased immersion time.
Does anyone have any idea why we are getting such different results with different alloys? I know there is some variation in coating between alloys, but these are drastically different results. We’ve also tried 2024 panels from different batches, same problems.
If anyone has any ideas or advice, it would be greatly appreciated.
Thank you in advance,
Zander Naes
– Denver Colorado
December 28, 2023
? Does the prep cycle you use for the 2024 remove excess copper from the surface of the substrate?
F DiGiovanni
– Worcester, Massachusetts
January 31, 2024
A. Zander,
As DiGiovanni mentioned, your prep might be a contributing factor. To rule out, mechanically clean (wet scotchbrite and rinse) a panel and Iridite alongside with a panel normally prepped. Do you get the same results?
In a past life, we used Iridite 14 and had to operate at the high end of the pH range, if not a little higher. Still passed periodic tests.
If you’e alkaline etching the panels, don’t.
Willie Alexander
– Green Mountain Falls, Colorado
February 17, 2024
Aluminum How-To
“Chromating – Anodizing – Hardcoating”
by Robert Probert
You’ll love this book. Finishing.com has sold a thousand copies without a return request 🙂
Q. Good afternoon. We recently made up a new bath of iridite 14-2 after multiple issues with an aged bath. The newer bath was made up in a separate/larger tank. The old tank was filled with a caustic cleaning solution. We did dump refill, dump refill to purge the tank. After making the new tank, the solution has maintained an orange color. My experience this is an indication of a solution with a higher pH. However when checking the pH it is within range. We did not heel or seed the new tank with the old solution, we felt it was severely contaminated and aged. We did attempt to condition the tank by suspending aluminum scrap pieces but did not see any changes. We are experiencing accelerated conversion rates on 2024 causing loose powdery coatings. The color of the bath is really concerning.
Steven Sanchez
– Arizona
April 1, 2026
A. How are you measuring pH? If by meeter, then standardize on pH 2.0 which is close to where you want to measure. If by paper, there is one pH paper which I cannot name here, with a range 1-2.8 that is accurate enough for 14-2.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Q. Robert,
I appreciate the response. I am measuring via meter using a 1.68 buffer for verification. We are still experiencing an accelerated 2024 loose coating that wipes. We do use an iron/nitric based deoxidizer. My first time using this type of deoxidizer.
Steven Sanchez [returning]
– Phoenix, Arizona
May 19, 2026