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topic 45728

How to eliminate powdery condition of Alodine 1200S

A discussion started in 2007 & continuing through 2017


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.


simultaneous (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, sulfates, 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
- Goleta, California
contributor of the year 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 continues to benefit from.


A. Do not know your process, just talk in general:
1. do not caustic etch 2xxx alloys;
2. PH 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 probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como

August 5, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,

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


- Chihuahua, Mexico

August 7, 2012

A. Hi Beatriz.

As you can see, a similar question was asked and answered in the past, so we appended your inquiry to that thread. If you have remaining issues after reviewing this, I'd bet that Robert Probert [a supporting advertiser] can help. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

October 9, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

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 10, 2017

A. Try a new deox in a bucket AND review the calibration of the pH meter, especially at that low pH.

robert probert
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina

October 11, 2017

A. Clay

I believe your pH may be the cause. Take a bucket of the Alodine and incrementally bump the pH to see what works. We have found better results at the higher end of the pH limit.

Willie Alexander
- Green Mountain Falls, Colorado

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