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Letter 4044
Corrosion Resistance of Alodine Treated
Aluminum
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I am building a home built airplane constructed primarily of 2024
T3 Alclad. Most of the parts get an acid wash
(
Alumiprep-33 [link is to product info at BoatersWorld]) followed by
a dip in Alodine
(Iridite?) and finally a
coat of primer. My question is: What happens to the corrosion
resistance of the alclad if some of the parts don't get a good coat
of primer? Does the Alodine increase or decrease the rate of
corrosion?
Patrick Armstrong
- El Granada, California
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Chromate conversion coatings ("Alodine") have a dual purpose. They
act as a good paint base. They also protect the material from
corrosion (theory is that a cut in the film may allow hex-chromium to
'bleed' into the scratch in a wet environment and protect the exposed
material - true? I don't know). Alclad is much more corrosion
tolerant than bare material, in that the cladding typically contains
less in the way of alloying elements. Parts inside the airplane are
often left in Alodine, only. However, I would endeavor to get good
primer coverage on the parts, just in case the Alodine application is
not what it should be - it is a lot more difficult to do properly
when you cannot immersion process the details.
Mark McGlynn
- Oklahoma City, Oklahoma
.
Hi, l looking for the same info for clear Iridite.
Joseph Chow
- Bayan Lepas , Penang , Malaysia
March 1, 2009
Hi, Joseph. Alodine and Iridite are two trade names for
Mil-DTL-5541 [link is to spec at TechStreet] conversion
coating. So Mark's answer applies as well to Iridite and to Alodine.
Good luck.
Regards,
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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