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How to eliminate powdery condition of Alodine 1200S

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.

Q. Hello!

I have chemical conversion coating process with Alodine 1200S.
I want to correct of powdery coating condition on my parts since a month ago (at that time I¡¯ve dumped and recharged my Alodine bath totally).
In my processing, small parts are free from powder and show very beautiful appearance, but unusually, big skins (which is aluminum 2524-T3 Clad, 4.8 by 1.8 m big) show powdery condition.
At this time the pH is 1.44 (1.3~1.8 control) and the concentration is 2.12 oz/gal (1.2~2.8 control).

I want to make sure what kinds of variables are affected to powdery condition and how can I solve this problem.
Thanks in advance.

D.Y.YOO
ENGINEER - BUSAN, KOREA
2007

A. Get the 'Technical Process Bulletin' for Alodine® 1200S, available from its manufacturer, Henkel. Your concentration is 2x the usual upper limit. From page 3: "If the ALODINE coating is powdery, the cause may be one or more of the following: A. The work has been improperly cleaned and/or rinsed. B. The concentration of the ALODINE coating chemical(s) in the bath is too high. C. The ALODINE 1200S bath has become contaminated with phosphates, sulphates, chlorides, or some other contaminant (analysis required). D. The coating time is too long. E. The bath temperature is too high. F. The Free Acid of the DEOXYLYTE final rinse is too high (should not exceed 7.0) G. The pH of the bath is too low for the concentration selected." Your solution parameters (low pH, excessively high concentration) probably have greatly accelerated the coating rate. This makes it difficult to immerse and remove large parts with any expectation of a uniform coating top-to-bottom. The cladding is high purity aluminum (99.3%) which must coat very rapidly in your conditions. Try using a pH 1.65-1.70 & a concentration of 0.95-1.05 oz(wt)/gallon [store 1/2 the solution in clean polyethylene drums for future make-up]. Also, the bath life is greatly increased by using DI water for rinsing prior to the ALODINE bath and for solution make-up. Ken Vlach [deceased] - Goleta, California Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015. Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from. A. Do not know your process, just talk in general: 1. do not caustic etch 2xxx alloys; 2. pH is better at 1.6-1.8 3. immediate spray rinsing after Alodining followed by immersion rinsing with manual agitation (less than 30 sec.) John Hu - Singapore A. First be sure you are using a mixed acid deoxidizer on that high copper alloy. Raise the pH to 1.8 with ammonium hydroxide, and that will slow the reaction then lower the concentration to 1.8 oz/gal and that will slow the reaction, then the coating will not "powder". Robert H Probert Robert H Probert Technical Services Garner, North Carolina

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Q. Dear Sir,

How come aluminum parts sometimes come out with powder presence when Alodine 1200s is applied (immersion process)? Does it have to do with the immersion duration time?

Regards!

BEATRIZ ENRIQUEZ
- Chihuahua, Mexico
August 5, 2012

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Q. Alodine 1200S is running 1.08 oz/gal. and 1.55 pH and 6061-T6 test panels are coming out a little powdery (parts are looking good). Could it be because of the test panels or is my concentration and pH off?

Clay Cheatham
- Magnolia, Arkansas, USA
October 9, 2017

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Troubles with Alodine 1200s

Q. Good Morning!

Summary of Problems: Inconsistent coating, Salt Spray Failure, Powdery Finish, Clear Finish, Finish bouncing back and forth between extremes when troubleshooting or changing parameters.

I have read as many discussions on this topic as I could, tried everything I could, to no avail. Here I am, please bear with me as this will be a long post with many details!

As a history, our company moved into a new facility in February, and switched proprietary brands from Iridite 14-2 to Alodine 1200S at that time, to open doors for Boeing Accreditation on Chemical Conversion coating. I had the Iridite 14-2 dialed in perfectly at the last shop. Perfect Salt Spray results (on 2024-T3), and a stable composition/maintenance schedule.

From day 1 of Alodine, we have experienced issues all over the board.

-10/26/17: Initial Bath makeup of 2.058 oz/Gal (Boeing guidelines recommend 1-3 oz/Gal for Alodine 1200s immersion, Henkel recommends 1.0 oz/Gal for immersion, 2.0 for brush application) (Bath sat unused until January 2018)
Initial Salt Spray results qualified us at a 15 second immersion for Class 3 coatings (electrical conductivity) and a 45 second immersion for Class 1A (maximum corrosion protection).
Coatings were spotty with runs/sagging colors, non-uniform appearance, some alloys powdered or didn't take coating at all, etc... pH fluctuated between 1.4-1.7.
We tried etching, no etching, deox, no deox, short immersions, long immersions, higher temperatures, lower temperatures, high pH, lower pH, etc...
Re-read the technical data sheet and decided to cut the concentration of the bath.

-2/26/2018: Bath Cut to reduce concentration to 1.33 oz/Gal. pH of 1.6, set point of 75 °F.

-3/5/2018: Initial Salt Spray Failure @ 1 minute processing. (pH of 1.8 that day)
We seemed to dial in the visual appearance for a few weeks, though Salt Spray had failed.
Panels and parts looked pretty good for a while, but still issues with inconsistent visual coating. Very spotty, some areas look clear, others are iridescent gold/orange/pink.
Then slowly the coating lost coloration until all parts ran were almost clear (including our Salt Spray panels).
-4/3/2018: Replacement Salt Spray Failure @ 3 minutes processing. pH of 1.5, 1.29 oz/Gal.
-4/3/2018: April Salt Spray panels Failed at the same parameters as the replacement test.
-5/3/2018: Upon receipt of the April failure notification, we immediately dumped the bath and rebuilt @ 1.28oz/Gal. 1.6 pH, and management mandated constant air agitation in the gold chem tank, unless parts were being ran. We proved with our previous proprietary gold chem that that was incredibly detrimental to coatings, but if we didn't agitate at all, we would slowly lose color in the gold chem coatings. We ran tests and narrowed down an air agitation schedule that worked to retain the color of the coating, but did not cause dark powdery coatings. This schedule was Monday, Wednesday, and Friday mornings for 1 hour.
Since management mandated the constant agitation, we have since had dark powdery coatings that wipe off or are removed with tape during the masking process.
(I would also like to note here that we do not wait 24 hours for the gel to cure prior to masking parts)
-5/17/2018: I provided Management with my failure investigations, which discussed Silica contamination in our tank. Between finding silicone plugs in the tank during the rebuild, we have been etching/deoxing a lot of Cast Aluminum parts lately. Testing showed 44 ppm of SiO2 in our Chemfilm bath. (I sent out a sample of the original bath alongside the new bath built on 5/3. New bath tested at 33 ppm of SiO2.) After this information we scheduled an immediate rebuild of the brand new tank...
-5/19/2018: Dump of tank, scrubbed out the tank with dilute NaOH & red abrasive pads, much rinsing, and rebuild.
-5/21/2018: Powdery coatings rubbing off, tape pulling coating off, etc... Waiting on results from SiO2 testing of this new New bath, plus our incoming tap water.
-5/22/2018: The panels ran last night by our swing shift that the coating was 'wiping off' of, and are now set, and will not wipe off.

Our Process:
Alkaline Clean: ~140 °F, ≥ 9.5pH, 17oz/Gal
Spray Rinse (pulled from Immersion Rinse next to it)
Immersion Rinse
Alkaline Etch (used only when required): 4.0 oz/Gal, Pre-penetrant/Boeing regulated parameters. 99 ° F.
Spray Rinse (pulled from Immersion Rinse next to it)
Immersion Rinse
Nitric/Iron based Deoxidizer: <1.0 pH, 50 g/L Fe2SO4 content, 34 g/L Nitric content. Cu content of <0.4 g/L (Usually sits at 0.026 g/L) 80 °F
Spray Rinse (pulled from Immersion Rinse next to it)
Stage 2 Counter flow Immersion Rinse
Stage 1 Counter flow Immersion Rinse
Alodine 1200s: 2-4 minute immersion, 1.6-1.7pH, 1.3 oz/Gal, 80 °F.
Spray Rinse (pulled from immersion next to it)
Ambient Immersion rinse: 3-5 minute immersion

I am about to drop the temperature, raise the pH, stop agitating the tank constantly, and see where that gets us.
Any insight or suggestions on what else I can do would be very much welcome!!

Kai Gussman
Lab Manager - Arlington, Washington, USA
May 22, 2018

Thank you for your response! 1. I previously examined the panels with a 10x loop and I did find atmospheric pitting in the graining on the 2024-T3. We ordered new material with the plastic covering. We then ran the old material and the new material under the same parameters but on different days, and sent both for Salt Spray testing. At that time, the New material Failed, and the Old material (with the pitting) Passed!! Still stumped on that one, unless it was a completely different issue. 2. We use a three point pH verification; 1.07, 4.65, and 9.23 with a temperature considered pH meter. We calibrate the meter daily before use, and re-calibrate or re-verify if a reading seems off. 3. We continuously agitate the air in the Deox. 4. We have had problems in the past with processors not deoxidizing/desmutting panels/parts long enough. I am still arguing with Managers and Processors about that. I will look into this as a potential - especially with the research I have done with the silica contamination (from etching/deoxing cast aluminum) potentially hiding out in the deox. We have replaced the Alodine bath (and scrubbed) but we have not replaced the Deox yet. I suppose that is next on our list. Update: Yesterday I raised the pH to 1.8, dropped the temperature to 75F, and physically locked out the airline that was being used to agitate the Alodine bath (the lab holds the only key to the lock and we will be agitating the bath for 1 hour three times a week, which is what gave us such wonderful results with the Iridite previously). Our Ops Manager ran panels at 2 minutes, and they were powdery. I told him to run at 30 seconds, 1 minute, and 1:30. 30 seconds - 1 minute looks BEAUTIFUL. 1:30 and it starts to powder. Now the challenge is to ensure we pass Salt Spray at those immersion times... If we can't, Boeing will not accredit us. Thank you very much Mr. Probert, I thought there shouldn't be a difference...and thank you immensely for the confirmation! Kai Gussman [returning] Aero Finishing, LLC - Arlington, Washington, USA A. Good Morning Kai Please refer to the following Finishing .com thread no.: 44433. "Close Looping" an Aluminum De-Ox System … starting at November 2nd. I have to say this forum is great … Thank You to all the past contributors who have aided my success. I am glad I can give back from my experience. I do not consider my self to be an expert, I have just done this more than 0 (ZERO) times. I have just completed the journey you are starting. It has been 6 months with passing results on both 2024-T3, 6061-T6 coupons to MIL-DTL-5541F Type 1 and Class 3 Specifications. Testing includes, 168 Hour Salt Spray, Contact Resistance and Paint Adhesion Testing to a 5A Rating. The lessons learned: #1 Do not use the Caustic Etch. #2 If using a proprietary product (the product manufacturer you stated), consult their experts for guidance. They will tell you to use their full line of proprietary chemistries, Cleaner/Deox/Chromate. This was the path I had followed. #3 Do Not Use DI water after the Deox. #4 A semi Automated Titration System enabled the daily titrations to be performed in under one hour. Allowing for higher accuracy and control of the bath chemistries. If you are performing manual titrations do not allow for distraction. The bath composition is critical. #5 Track the daily Chemistry measurements on an Excel Spreadsheet and this will aid in monitoring drag out and adds. I am still tracking trends for understanding when to perform additions and when to dump the tank. The process I follow is: Cleaner Immersion 140 °F 15% / Vol:      5 Minutes Closed Loop DI Ambient Immersion Rinse: 15 Seconds Closed Loop DI Ambient Spray Rinse      15 Seconds Water Break Test                         1 Minute C-IC-6MU DEOX/NITRIC Ambient Immersion 96.07 g/L and 6.55 g/L (Suppliers Recommended Proprietary Product Mixture) Immersion Time:                  8 Minutes Static Tap Water Immersion Rinse 1 Minute Static Tap Water Immersion Rinse 1 Minute Tap Water Spray Rinse            1 Minute Chromate Ambient Immersion currently running 14.3 mg/mL and 1.44 pH Immersion time for Class 3 is:          1 Minute DI Immersion Rinse Closed Loop DI Ambient Immersion Rinse 15 Seconds Drip Dry-Dab the bottom of the panel-No Compressed Air is used to Dry the Coupon panels. Wear Clean cotton or Nitrile glove before handling. Stand the panels in a Blue Metro Tote on edge. Wait a Minimum of 24 Hours to semi cure. Individually Wrap in Uni Wrap 30 MPI VCI Paper. Perform the testing regiment. Wait for Results I hope this helps you in your success. Cheers Kurt Krueger - Lexington, Massachusetts

 Good Afternoon and Happy Friday!

Mr. Krueger,
Your referenced post is actually the one that helped me discover our Silicate contamination problem!

Mr. Probert,
This morning, our tank read at 1.7 pH with our normal calibration.
I just re-calibrated the meter to a single point, with our 1.07 buffer. Sure enough, our pH now reads at 1.56 . I am issuing a change request to bring it up to an actual 1.8!
I will be changing our tank monitoring process for anything under 2.0 from now on. Thank you!

Yesterday I added an electric filter unit (sans filter) into the bath to provide mild manual circulation into the tank.

You recommended to leave a slight chem residue on the parts to dry (please correct me if I am misunderstanding) to aid in corrosion protection...
Our processors currently spray rinse and then 'soak' the Gold Chem in an ambient temperature immersion rinse for 3-5 minutes immediately post chemfilm. Is this something that will harm our coating? Right after that, parts come off the line and they are blow dried with compressed air nozzles, and stored in our "Dry Room" which is controlled to rise no higher than 120 °F. (My validation panels do not get compressed air, nor are they placed in the heated room. They are air dried in the Lab where I can keep my eye on them.)

I want to thank both of you, and this entire forum, for the help and resources provided. Absolutely invaluable.

Kai Gussman [returning]
Aero Finishing, LLC - Arlington, Washington, USA

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Q. How much pressure should be applied to detect the powdery condition tested in Alodine 1200S (yellow - brown)with 2024 aluminum?

When we run this material 2024, it has some powdery if the cloth is pressed a little bit, other alloys does not show powder even if the cloth is applied "hard" - rubbed to the surface.

Is there an "appropriate" level or specification of pressure to be applied?

Mauro Cardenas
Consultant - Mexicali, BC, Mexico
August 17, 2018