Letter 4044

Corrosion Resistance of Alodine Treated Aluminum 

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I am building a homebuilt airplane constructed primarily of 2024 T3 Alclad. Most of the parts get an acid wash (Alumiprep) followed by a dip in Alodine (irridite?) 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, CA

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, OK

Hi, l looking for the same info as clear iridite.

Joseph Chow
- Bayan Lepas , Penang , Malaysia

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