Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing 1989-2024
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Alodine is not properly coating some aluminum alloys
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 PRF-5541 / MIL-DTL-5541
[on DLA] is the most commonly cited spec. "Alodine" and "Iridite" are trade names. "Chem film" is a slang term for the process.
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Q. My test panels for salt spray are not coming out as dark as they were. I'm chem-filming 2024-T3 panels, with Bonderite M-CR 1200s Aero Chromate (Alodine 1200s). It's more like a clear Alodine when they come out. All my tanks are at the right temp, pH is within parameters, so is my concentration. I'm lost on what to do.
David AndersoonChem-film - Phoenix,Arizona
May 30, 2023
? Hi David,
What's your DeOx, and how do you manage it? And out of curiosity, do you also process castings on that line?
Do you have any protocols for tracking tank contamination?
Are the panels still passing salt fog?
Rachel Mackintosh
lab rat - Greenfield, Vermont
June 25, 2023
⇩ Related postings, oldest first ⇩
Q. I am the QC and lab technician at a small sheet metal manufacturing shop in N. Idaho. We have just switched to the Alodine 600 and are having some mind-boggling problems.
The 600 coats 2024 BR and 7075 CL aluminum alloys good, but coats 2024 CL, 7075 BR, and 6061 aluminum alloys very poorly (the coating is streaky and light). Our biggest problem though is 7075 T0 BR .063 aluminium that has been heat treated to T62. We cannot seem to get an adequate coat of the 600 on these parts.
The chemical properties of the 600 are in the middle range of concentration and pH, and toner 22 has been added.
All parts are cleaned in an alkaline cleaner, then deoxidized, then processed. All chemical baths have 2-step immersion rinses after them.
Any help at all would be appreciated here!
Benjamin Curto- Sagle, Idaho, USA
2000
A. Ben
I can't help but feel your desmut / deoxidizer is the problem. I might suggest a nitric dip possibly or a fluoride one. Sounds like you have a film that is preventing the 600 from penetrating
Drew
Drew Nosti, CEF
Anodize USA
Ladson, South Carolina
Q. Hi,
I'm having the same Alodine 600 problem with 6061 and 5052 Al. The only info that I have found to date is that sulphate contamination will cause Alodine 600 from adhering.
Needless to say I had all rinses, etc. analyzed/changed and still the problem appears. My alkaline cleaner & desmut/de-ox tanks are new and still the same problems crops up on 6061 & 5052 Al. I have also tried a Fluoride one to no avail. What I have tried is making a small bucket of Alodine 600 solution at 30 °C (our tanks are at 22 °C). At 30 °C I seem to be getting better adhesion but still it is streaky and a lot lighter than at 22.
Any info or anything I can experiment with to solve this problem will be greatly appreciated.
Marc Nanni- Montreal, Quebec, Canada
2000
A. I have experienced that same problem before, tried every acids/alkaline clean but got the same negative result.
This may not be applicable to your requirements but I found out that scrubbing with scotch brite just prior to Alodine dip solved the problem.
dado macapagal- Toronto, Canada
2000
A. Hi,
We have been finishing 7075 bare and 2024 bare all tempers for several years with Henkel 600 & 120O. I agree with the gentleman from Canada -- the key is scotch brite cleaning prior to treatment. Also be sure you monitor the pH.
Joe Harmuth- Madison, Connecticut
2001
Multiple threads merged: please forgive chronology errors and repetition 🙂
Alodine 600 help for dark gold conversion coating
Q. I'm pretty new to this so don't be to hard on me. I would like to improve my results in color and consistency. I'm using Alodine 600 to plate 6061 and 2024 aluminum parts. The desired color is a dark gold. I'm using a phosphate acid for 3-4 min. Then dip in cool water and spray with hot water then back to cool for 3 min. Alodine for 3 to 6 min. let hang 30 sec dip in cool water 10 to 15 sec. Dry with air heater. I recently installed a heater in the Alodine to bring it to 70 °F. Since then the parts have come out lighter gold and the 2024 parts don't seem to plate at all. The acid strength and Alodine strength are at max recommended. Do the times seem off? Any help would be greatly appreciated.
Chris Fischer- Chippewa Falls, Wisconsin
2006
A. The product you are using is relatively new on the market and is very sensitive to surface preparation. I suspect that the phosphoric acid deox is not doing a complete deox job - switch to 30%/vol Nitric Acid, or better still, call your chromate vendor, discuss the problem, with his technical people, then I am sure they will recommend a mixed acid product that will work better ahead of their chromate formulation.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
How I can get a good appearance of Alodine 600?
Q. Dear Sir
We purchased material from Henkel to do Alodine 600. Our process followed the material Spec, but no matter how many times we tried,we always got a poor appearance: The surface appears "cloudy",the color on the surface is not uniform,it seems that some place get a very thin coating--it's even worse near the holes on the parts. Meanwhile,another company processed our parts,got a very nice appearance(I wanna say our machining should be all right.)
Expecting your advice!
- Chengdu, Sichuan, China
January 12, 2009
A. If someone else got good results, then there is a high probability that there is something wrong with your process.
There is also a possibility that you got a bad can of material. Years ago, we had a problem with 1200 and the manufacture denied anything could be wrong with their product. With much complaining, they pulled the QC sample and lo and behold, it did not meet spec. We had to switch to a competitor because they could not provide another lot number on a reasonable time frame. It is rare, but it happens.
Ask who you bought it from to send their tech service rep out to troubleshoot the problem. When you buy proprietary material, tech service is expected to go with it.
- Navarre, Florida
Q. Thanks for your reply! If suppose that our material for the process is OK. Any detailed situation would cause "Water Stain" or
"thin coating"near the holes (Please see the Picture on 1st floor).
I think maybe there is something wrong when we during washing and drying after anodizing.
Many thanks
- Chengdu, Sichuan, China
A. Just would like to share my experience. The white areas usually are the spots that water gets together and stays there. We have to use air blow to dry parts right after Alodine rinsing. You can check whether there is white stain after Alodine dipping?. If there is, so it is not the same as my case, :). Hope it's useful.
Tapanon Satjaratanchot- Samutprakarn, Thailand
Q. We run only the Alodine 600, were having some problems with the streaks and turned to scotch brighting prior to the Alodine application. We have recently completely rebuilt the chemicals in the tank and are having issues with it looking real spotty, coverage is there but looks terrible. pH is 1.68 and tank runs at 20 °C. Have been battling this for a while. Any suggestions?
David Vance- Wichita, Kansas USA
August 15, 2014
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A. David - Colorado Springs, Colorado A. We don't use Alodine but we do encounter the situation you described. For us, a spotty, non-adhering coating indicates our pH is to low. Depending on the size of our tank, we will add a cup or two of sodium hydroxide and retry. Usually 1 addition will get it sticking again. Justin Brooks- Rock Island, Illinois |
