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Is this aluminum OK to use???

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photodoctor

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Joined
Dec 28, 2010
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6
Location
new washington, ohio usa
I'm starting construction on a scratch-built metal airplane. I have some sheets of 2024 T3 which has been sitting in my garage for years and I'm not sure whether I should use the stuff (refer to attached photo). It never got wet and the metal doesn't seem to be pitted. I haven't tried scotch-briting it with lacquer yet but the little bit of rubbing I did with a piece of steel wool seemed to shine it up. I'm new to metal work so any help will be appreciated.

Also, these sheets are labeled, "Bare Alcoa", this means that they'll NOT Alclad sheets, correct? My plans call for Alclad metal for building the wing ribs. Can I use this stuff and simply treat it with corrosion protection?
 

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djschwartz

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Jun 21, 2008
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Portland, Oregon
Never, ever use steel wool on aluminum. Minute particles of steel will break off from the wool fibers and embed themselves in the pores of the aluminum. These will become future starting sites for inter granular corrosion.

If your plans call for Alclad, I would use it. 2024 is stiff and strong but has about the poorest corrosion resistance of the commonly used aluminum alloys.
 

photodoctor

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Dec 28, 2010
Messages
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Location
new washington, ohio usa
Thanks for the reply. Another guy emailed me and said this: 'Acid etch, alodine, and prime and you're good to go for your homebuilt. Alclad doesn't add a lot as long as you're properly coating the surface'. Does anyone have any additional thoughts for me before I start looking into "Acid etching, alodine and prime"?
 

jumpinjan

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Joined
Oct 3, 2004
Messages
313
Location
Dayton OH
Well, its really cleaning with a metal conditioner rinse with water, then alodine, rinse, then epoxy prime. That would be a good system to use on aluminum.
Jan
 

Dan Thomas

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Sep 17, 2008
Messages
5,473
2000 series alloys have lots of copper in them, and as Schwarz says, it corrodes in no time flat due to the copper's electrolytic action. That's why 2024 has pure aluminum applied to both sides, 2% of the total thickness: the aluminum oxidizes and creates a stable barrier to further corrosion. Priming your bare 2024 might help, but any scratch would be big trouble.

When I was in the air brake remanufacturing industry, we encountered a line of brake actuators made of a high-copper alloy, and they would rot away in months. Since they contained a hugely powerful spring to apply the brakes in the event of air pressure loss, those springs were exploding out of the actuators while the trucks were on the highway, and some in the shops, and some folks were killed. It was a mistake made by a company that hadn't done its metallurgical research. We didn't rebuild any of them and very carefully dismantled them for disposal. So, see, I'm cautious about substituting one alloy for another.

One might regret saving the money. But then, what would bare 2024 be used for?

Dan
 

kennyrayandersen

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Jun 6, 2011
Messages
72
Location
Ft. Worth TX
I tried twice to post a rather long response but it timed out twice and I don't feel like doing it again. Bottom line 2024 T-3 bare sheet is used all the time in commercial AND military applications; so, I'm guessing they aladine it or something but we don't use clad (I here it's not worth the weight.
 

thetford

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Joined
Feb 15, 2009
Messages
13
Location
Birmingham, Alabama
Structurally your ok to use it... but most likely you will have corrosion problems at a later date, espicially since you are a "novice" sheetmetal worker. Take a high-speed with a scothbrite & MEK and clean the surface, then treat with Alodine for about 20 to 30 seconds, wash with water, fab your parts and then zinc cromate them.
 
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