Letter 33020

Alodine alone for aircraft corrosion protection? [Arizona] 

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I am building an aliminum aircraft in a very dry climate (Arizona)and would like to keep the weight down. Would I have adequate corrosion protection on the internal parts (ribs, spars, etc.) if I used only an Alodine (chromate conversion coating) bath coating without additional primers?

Thanks in advance for your help,

Ron

Ronald Burden
Hobbyist - Cottonwood, AZ, USA

It is possible, but there are better choices.

I've seen parts that we've chem-filmed (Alodine is just a tradename for one of the chemicals that can be used to do the chemical conversion process) exposed outdoors for years without corrosion, but it isn't really what the coating is made for. You'll get MUCH better results by anodizing the parts - the weight difference will be very minimal, you can dye the anodize for cosmetic purposes, you'll get better scratch resistance from the anodize, and the corrosion resistance will be much higher. There may be a slight difference in price, but it probably won't be as much as you'd expect.

Jim Gorsich Accurate Anodizing Inc. Compton, CA, USA

Ribs, stringers and such are chemfilmed and not painted in at least a few planes. If it is open to physical abuse, it would normally be painted afterwards. Individual moving parts are sometimes anodized.

James Watts
- FL

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