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topic 39602

Can steel be anodized or Alodined?

A discussion started in 2006 but continuing through 2017


Q. Will Alodine have the same desired effect on steel as on aluminum?

Joseph Raiker
United States Marine Corps - Warrington, Pennsylvania


"Alodine" is a Henkel trade name for their line of chromate conversion coatings for aluminum and light metals.


A. Hi Joseph. No, chromate conversion coating is not applicable to bare steel, although steel may be zinc plated and then have a chromate conversion coating applied. Please explain your situation. Thanks!

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


Q. An anodized part made of steel had all of the anodizing stripped away . The engine guys had a crazy idea that Alodining and priming the part would have an equal effect. I disagreed on the grounds that the manual had no repair procedures for this gear once the anodize had been removed.

Joseph Raiker [returning]
United States Marine Corps - Warrington, Pennsylvania


A. To my knowledge steel cannot be anodized, so I don't quite understand what you are saying about "had all anodizing stripped away". To my knowledge, plain steel can't be chromated either.

If the part is actually aluminum, chromate conversion coating is not the equivalent of anodizing, but it does afford substantial corrosion resistance and is sometimes used for repairs to anodized parts. Good luck.

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


Titanium can be anodized. See, for example, AMS 2488 [link by ed. to spec at TechStreet].


thumbs up signThank you for helping us out with this. The manual for aircraft engines actually does say that this particular metal is anodized. It certainly isn't aluminum or any non-ferrous metal, so we simply assumed that it had to be steel or titanium. Whatever the case, they are anodizing it and not using Alodine/primer coating. Thanks again.

Joseph Raiker [returning]
- Warrington, Pennsylvania, USA

sidebar2 January 22, 2017

A. Ferrous metals can be treated with a mixture of gallic and formic acid. It is a chemical conversion process similar to alodine.

Matthew Finkelroy
- tucson, Arizona, USA

January 2017

thumbs up signThanks Matthew, sounds interesting. But I'm totally unacquainted with such a process; is there a standard or a technical article available about it? Thanks.


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

May 25, 2017

Q. Hi,
Please let me know:
Can Stainless Steel be Alodined?


May 2017

A. Hi Ferguson. To my knowledge, no it cannot. Unfortunately, I can't imagine that this answer has greatly expanded your understanding or helped you much. Sorry. To get educational and truly helpful answers, and to attract readers to participate with your possibly interesting situation, please carefully explain it. Thanks!


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

May 31, 2017

A. Ferguson,
The general answer to "can I do X surface coating on stainless steel" is:

Probably not, or if you can it's really difficult, and really why would you want to anyway?

Most of these coating methods we talk about were developed as a corrosion protection for the underlying metal, but stainless steel was developed for the metal ITSELF to be corrosion resistant. Yes, you still need to do the passivation treatment, but the point of the stuff, and the extra cost you pay for it compared to other materials, is you can count on it pretty well to not rust with just the original bare metal surface, not a coating.

Even things as universally applicable as paint/powder coat/clear lacquer coat, if you are going to put that stuff over your stainless steel, or may as well have saved some money and used mild steel in the first place.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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Will Alodine harm 4130 bolts?

August 14, 2017

Q. We have anodized doublers with aluminum (CAD Plated) inserts and CAD plated washers with a 4130 steel bolt installed on some Aircraft Parts.

When we asked the MRO team to alodine and prime the anodized parts since they have worn down over time, they did. We discovered that they also alodine treated the 4130 steel bolts as well.

On discovery we want them to take the bolts off and replace them. The airline is requesting that we allow them normal maintenance cycle (about 3 months) before they remove the bolts. The doubler is not a system critical part, and no safety issue.

James DelPinto
- Huntington Beach, California, USA

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