USAAC unpainted aircraft oxidation
- Thread starter gjs238
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ccd11
Recruit
Aluminum alloys will oxidize, but pure aluminum will not. Pure aluminum, though, is not nearly as strong as aluminum alloys.
Most sheet aluminum used on aircraft is aluminum alloy coated with a very thin layer of pure aluminum, called Alclad. The alloy provides the structural strength, and the thin aluminum coating provides corrosion protection.
In theory, Alclad doesn't require corrosion protection. But since the pure aluminum coating is very thin, long term, there's likely to be nicks and scratches that expose the alloy, providing a foothold for corrosion.
Most sheet aluminum used on aircraft is aluminum alloy coated with a very thin layer of pure aluminum, called Alclad. The alloy provides the structural strength, and the thin aluminum coating provides corrosion protection.
In theory, Alclad doesn't require corrosion protection. But since the pure aluminum coating is very thin, long term, there's likely to be nicks and scratches that expose the alloy, providing a foothold for corrosion.
BombTaxi
Tech Sergeant
Thanks for the information ccd, and welcome aboard 8) I thought Alclad was just an expensive way of finishing model kits 
Great thing about this forum, every day is a schoolday 
Surely this must have caused a major headache for maintenance crews? Aside from the obvious effects of combat damage, the everyday wear and tear of flying through the atmosphere at 150 mph+ must have caused abrasions, as well as more mundane causes such as crew ingress\egress and varying degrees of FOD. Out of curiosity, does anyone know what kind of schedule there was for respraying on operational squadrons?
Great thing about this forum, every day is a schoolday Surely this must have caused a major headache for maintenance crews? Aside from the obvious effects of combat damage, the everyday wear and tear of flying through the atmosphere at 150 mph+ must have caused abrasions, as well as more mundane causes such as crew ingress\egress and varying degrees of FOD. Out of curiosity, does anyone know what kind of schedule there was for respraying on operational squadrons?
I'm not sure if I can agree with that fully, I'm afraid
Aluminium is remarkable for its ability to resist corrosion due to the phenomenon of passivation. So the pure aluminium starts oxidizing ( corroding ) immediately it meets oxygen. In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometers thick. Of course the pure aluminium can be protected additionally by a coat of a preservatives. But because of the deposition of a layer of oxide it peels usually. The pure aluminium is quite pliable and rather can't be used for making parts that have to be stringers for instance. That's true.
Therefore aluminium alloys appeared. The first a new corrosion resistant aluminum product which is markedly superior to the present strong alloys appeared in 1927 and was called Alclad. Its using resulted in greatly increased life of a structural parts. Alclad is a heat-treated aluminum, copper, manganese, magnesium alloy that has the corrosion resistance of pure metal at the surface and the strength of the strong alloy underneath. Although Alclad has had the corrosion resistance its needed to be preserved because of these nicks and scratches that might always happen. Because it's an alloy these coats don't peel so easy.
But metal is metal and the oxidizing process can be noticed often.
Hmmm, learn something new everyday...
ccd11
Recruit
mikewint
Captain
Wurger, excellent response. Other metals (alloys) can also form this oxidized protective coating. Iron which oxidizes (rust) can form this coating with the addition of chromium (Stainless steel) the chromium reacts with oxygen very quickly but the coating is invisable to the eye and as such appears unchanged. scratches/nicks which breach the coating quickly oxidize reforming the original coating. Iron containing phosphorus can form such a layer: the Iron Pillar of Delhi is a prime example. Titanium also forms such a passivation layer.
Other metals such as nickel have very, very, slow rates of oxidation and as such are used to coat metals with higher rates
Other metals such as nickel have very, very, slow rates of oxidation and as such are used to coat metals with higher rates
Edgar Brooks
Senior Airman
Don't forget that aircraft didn't last (nor were they expected to) as long as your car. 25 hours flying, and they had a service; 100 hours, and it was likely to be a major service, possibly involving a trip to a Maintenance Unit, with any damage repaired, or the whole item replaced, then repainted, before returning to its unit, or being sent to another. Obviously, I don't know the USAAF's system, but RAF aircraft were not just left out in the open, to corrode, since groundcrews took a pride in "their" aircraft's condition, and I'll bet that American servicemen were the same. Pilots often said that they felt that they were only grudgingly loaned a particular aircraft; Johnnie Johnson apologised to his crew, on the one time that he was hit by enemy fire.
Edgar
Edgar
