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topic 56597

Effects of Alodining on steel inserts

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A discussion started in 2011 but continuing through 2018

January 27, 2011

Q. Hi,

We have an aluminium body. There are some steel inserts. We want to Alodine coat the body. However we are concerned about inserts. How can we protect inserts ? Are there any chemicals to protect steel from Alodine coating?

Mustafa KAPLAN
Designer - Ankara, Turkey

January 27, 2011

A. Hi, Mustafa

There are certainly masking agents for plating and anodizing. They can be caps and plugs, platers tape, waxes, brush on coatings, etc. But have you actually experienced damage to the steel inserts? Zinc plating and chromate conversion coating is routinely done on steel tubing, and although the unplated areas inside the tubing do not accept conversion coating, it doesn't seem to be harmed either. My feeling is that a brief immersion in Alodine will not harm the inserts, although I'll certainly yield the floor to anyone with specific experience.


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

January 28, 2011

Q. Dear Ted,

First of all thank you for your answer.

We have not tried to put inserts to the Alodine bath. However my colleagues insist about the damage especially on teeth of the inserts. They suggested to me using "stop of lacquer". Does it meet my needs?

Mustafa KAPLAN [returning]
- Ankara, Turkey

January 30, 2011

A. Hi, Mustafa.

Yes, stop-off lacquer will meet your needs perfectly if it is possible to apply exactly where you want it applied. Although anodizing will certainly destroy steel inserts, I remain of the opinion that Alodine (chromate conversion coating) does not substantially attack steel until someone tells me otherwise. I have no first-hand experience in the subject.


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

simultaneous January 31, 2011

A. By insert, I assume that you are talking about helicoils or similar.
The time in the Alodine is fairly short, so damage from that tank will be minimal.
The problem lies with the different prep solutions as well as the Alodine being trapped underneath the coil. This can cause long term damage. You will find that it is very difficult to mask off a helicoil and still have it Alodine right up to the coil.
If at all possible, add the inserts after the chemical process.
If it is absolutely not possible, find out what the company that did the blueprint and the customer want you to do. My guess is that they want you to mask it, but I would NOT provide any guarantee other than best effort. I personally would expect some failures on salt spray testing.

Some places apply zinc chromate to the coil or the hole prior to insertion. Being generous with this as well as using a thicker version may help.

James Watts
- Navarre, Florida

January 31, 2011

A. My experience agrees with Ted's. Immersion in the Alodine solution is generally less than 60 seconds and would have insignificant attack. For that reason it is usually not masked. Alkaline cleaning and etching also has no effect. However, if you have an acid etch in your cycle before the Alodine, that may (or may not) be a different story. The best advice that I have for you is to test it out on some sample parts and see if masking is necessary for your chemical cycle. I know of one case where the supplier elected to add a steel inserts after Alodine in order to avoid potential damage from chem processing, so that may be an option for you as well.

Jon Barrows
Jon Barrows, MSF, EHSSC
Springfield, Missouri

February 1, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Traditional process is to insert helicoils after passivation (chromate) in aluminum but what would happen if passivation was performed after stainless steel helicoil inserts were installed?

Would there be a concern of corrosion from leftover chemistries, or would the rinsing process of the passivation process be sufficient to remove any residual chemistries?

Bob Deyo
- San Diego, California, USA

March 8, 2013

A. No problem if you do not stay in the deox too long. In order to shorten the deox time, alkaline etch as long as you can without loosening the stainless steel inserts, then all the deox has to do is remove smut (rather than weathered oxide).

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
and co-author of The Sulfamate Nickel How-To Guide

March 23, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I want to use Bonderite C1C 33 [Alumiprep 33] as a cleaner on aluminum before using Bonderite 1001 (Alodine) as a protective coating. I have a few steel parts riveted to the aluminum. Will I damage the steel parts if they are exposed to the C1C 33? My plan is to use a submersion bath on the parts to clean them. Rinse with water. And a submersion bath in the Alodine, followed by a final water rinse. I believe this is the recommended process. My concern is about the steel parts contacting the cleaner.

Paul Willy
- Gardner Kansas USA

March 2018

A. Hi Paul. We've appended your inquiry to a thread where you can read that this is considered poor practice. If there is any practical way, you should always surface treat different metals before joining them together.

The question thus becomes what are these parts and how sensitive and crucial is the issue? If you are an aircraft maintenance shop, forget it. But if you are a hobbyist, trying to save a folding lawn chair with steel rivets and hinges, it's maybe worth a shot :-)

I would probably re-read Jon Barrows' response though, and consider cleaning the parts with an alkaline cleaner rather than Alumiprep 33 however.


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

March 23, 2018

A. No problem if you deox in ONLY ferric sulfate, with no other acids. this is the way armatures are done that have iron imbedded in the cast aluminum.; Make up ferric sulfate at 8 oz/gal, clean in an aluminum cleaner, skip the etch, and deox in the ferric sulfate. Keep the ferric sulfate air agitated or it will go to ferrous.

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

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