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topic 41155

Boric-Sulfuric acid anodizing BAC5632 Issues and Answers

A discussion started in 2005 but continuing through 2018


Q. We are having problems with our Boric-Sulfuric Anodize tank. We are getting some bad pitting and what looks like corrosion on our parts. This is the 2nd time this has happened in 3 weeks. The first time we suspected contamination of the bath, but now we have a brand new bath and it has my mind boggled. Please help me with any advice as to what our problem could be.

Tony Schmaltz
Plating Shop - Seattle, Washington USA


Q. Please send your answer for the problems of pitting in boric-sulfuric anodize process.

Kario Michael
- Lod, Israel


Q. We are having problems with our Boric-Sulfuric Anodize tank. We are getting some bad pitting and what looks like corrosion on our parts. I see same question but there was no answer.

Please, please, let me know why those pitting(or burning?) are generated and how to resolve this problem.

I.S. Hwang
Aluminum treatment - South Korea


Hello, I.S. There are several other letters on-line here about boric-sulfuric anodize, and several of them mention that the process is Boeing BAC5632. Are you following BAC5632?

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


Q. Yes, we perform Boric-Sulfuric Anodize in accordance with BAC5632 for Boeing parts.

I.S. Hwang
Aluminum treatment - South Korea


A. I.S.

It is a long shot but I would check for chloride contamination, particularly if the pitting coincides with a bath make-up or new solution(container) addition.

Willie Alexander
- Colorado Springs, Colorado

July 9, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir, we do Boric & Sulphuric acid anodizing.
After the process we get pits/ black pore-like things.
Please can you throw light on this?
Thanking you,

- Bangalore, Karnataka, India

July 11, 2013

A. We really need more information on your process parameters in order to come up with an insightful response but I have found that when I have had pitting problems they usually come from either too weak of a deox/desmut solution or too much time in the deox/desmut solution.

Tim Hamlett
Tim Hamlett, CEF
    aerospace metals distributor
Tamarac, Florida, USA

July 25, 2013

A. I think your problem is not related to anodizing. I had had same problem 4-5 month ago. I noticed source of problem was extrusion and storage conditions. Long time storage profiles's surface getting corroded. After caustic bath, these pits reveal and after anodizing you can see it. Solution: profiles not to wait too long time; avoid humidity storage; and also I wonder do you see these pits for bright profiles after anodizing? I don't see so far... because these profiles not treated with caustic.

Alaattin Tuna
- Sakarya, Turkey

Boric Sulfuric Acid Anodize tank analyses

May 10, 2016

Q. I am looking for a titration procedure with factor for boric acid and sulfuric acid. I am having difficulty getting the correct concentration for each and I've tried three different methods

Christy S
lab tech - Savannah, Georgia

simultaneous May 10, 2016

A. Christy, it would be helpful to know what 3 methods you have tried, so that your follow up reply is not I tried that and it does not work.
If this is to a Boeing spec (since they patented it) then they will have a specific way to test for it.
I will speculate that it would require a very good pH meter and possibly an autotitrator using a weaker titrant than what you are using. Boric has 3 inflection points that might be hard to find. Impossible with a rapid titration or normal 1.0N sodium hydroxide.

James Watts
- Navarre, FL

May 10, 2016

You can easily determine total acidity via a titration with 0.1 N NaOH to a phenolpthalein endpoint. I imagine that you could isolate the boric by titration to a method orange endpoint with the same solution. Plenty of stirring and slow the titrant.

dave wichern
Dave Wichern
Consultant - The Bronx, New York

May 11, 2016

thumbs up signThank you for all your help. Yes, I am using a Boeing spec for the titration procedure. The Procedure No. I used is B-281A of which uses 1.0 N NaOH as the titrant. I have started over and redone the procedure and finally got my end results in reason from what they were. I appreciate all the advice on this and will utilize it to my advantage. Thank you!

Christy Sanchez [returning]
- Savannah, Georgia

Pitting under the rack marks in Boric-Sulfuric anodizing

August 22, 2018

Q. We are experiencing pitting under the rack marks. This is a boric/ sulfuric process. It is only occurring on this part configuration. Does anybody have any suggestions as to what might cause this?

41155-1c   41155-1b   41155-1a  

Brandon Boyd
metal finishing - Holdenville, Oklahoma U.S.A.

August 24, 2018

A. Such big electrical contact, maybe acid residual when drying leads to these pits.

Tingqiang Wang
Zhejiang XIZI Aviation Industry Co., Ltd - Hangzhou, China

August 2018

A. Hi. The pictures might be deceiving me but those pits look so deep & severe that in my limited experience it doesn't seem likely they would happen in a short time solely from chemical reaction. I get the feeling something electrical is happening like a momentary short circuit, or dirty contacts not carrying any current during ramp-up then suddenly breaking through at higher voltage.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

August 24, 2018

A. The cause could be a poor electrical contact, probably the surface is uneven so only a small area is doing the electrical contact and that produces the burns.

Yohands Rey
- Chihuahua, Mexico

August 27, 2018

A. Brandon

What does the surface of the contact plate look like? Does it have the same pitting?

Have you tried unracking the parts prior to seal to see if the problem originates in the anodize bath? If you have residual acid trapped between the part and contact point, elevated temperatures might cause the pitting you are experiencing.

Willie Alexander
- Green Mountain Falls, Colorado

August 29, 2018

A. I don't suppose this appearance is "pitting" ... pitting is completely different. We can say "stain" as described. My advice: you can change rack design, or degreasing and neutralize duration can be much more, like 5 min. Because maybe profile's surface was dirty from normal level so in that joint area had effected as we see picture.

alaattin tuna
- Turkey,sakarya

August 2018

thumbs up sign  Hi Alaattin. Agreed that this is not what we usually call a "pitting defect", but it sure looks to me like quite deep etched craters, not a surface stain. Pictures can be deceiving: one of us sees stains, but one of us sees deep corroded indentations :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

September 4, 2018

A. Hi Ted, yes, I agree with you about "point of view" issue for some problems like this one ... but I think solution of this problem should be "one". In this situation I follow this way:
1- How often does this problem occur? for example, every rack or some racks ... also does the same problem occur on different profiles?
2- one of the key words in this situation is "survey". Is this problem emerging before/after anodizing or etching ... also sealing.
So we can collect and filter all the results and diagnose; after that, of course, treatment.

alaattin tuna
- sakarya,TURKEY

September 19, 2018

A. We have had the same problem as Mr. Boyd, however, not just on the contact areas. The deep pits in Mr. Boyd's photos are all too familiar to me while using boric/sulfuric anodize. I have never been able to nail down a cause. My tank will produce perfect parts for three months straight - then, without warning, an entire lot of parts will exhibit those monster-pits. The pits will appear at contact points AND at random areas all over the anodized parts. The pits are quite deep and generally will cause the entire lot of parts to be scrapped. Our parts are racked on clean and deoxidized racks and the contact points are as small as possible to reduce the likelihood of trapped solution. Pre-clean includes a deionized water rinse after deox.

Steven Haubeil
Aerospace - Wantagh, New York USA

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