Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Effects of Alodining on steel inserts
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?
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.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 27, 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?
- Ankara, Turkey
January 28, 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.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
January 30, 2011
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A. By insert, I assume that you are talking about helicoils or similar. - 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, MSF, EHSSC GOAD Company  Independence, Missouri  January 31, 2011 |
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?
- San Diego, California, USA
February 1, 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 H Probert
Robert H Probert Technical Services
Garner, North Carolina
March 8, 2013
Q. I want to use Bonderite C1C 33 [Alumiprep 33 ⇦this on eBay or Amazon [affil links] ] as a cleaner on aluminum before using Bonderite 1001 (Alodine) ⇦this on eBay or Amazon [affil links] 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 23, 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.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
March 2018
A. No problem if you deox in ONLY ferric sulphate, with no other acids. this is the way armatures are done that have iron imbedded in the cast aluminum.; Make up ferric sulphate at 8 oz/gal, clean in an aluminum cleaner, skip the etch, and deox in the ferric sulphate. Keep the ferric sulphate air agitated or it will go to ferrous.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
March 23, 2018
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Ed. note: For second opinions and additional discussions please see these related threads:
00664 "Chromate conversion coating on screwed & glued aluminum"
16006 "Chromate conversion coating aluminum parts having inserts"
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