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Old 07-08-2009, 06:30 PM   #1
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Different alloys and Thicknesses for the Skin

Hello,
As I weigh the costs and benefits of skin replacement using 2024-Alclad, am struck with the significantly higher price and more delicate nature of this alloy, compared to 3003, 6061, or 5052.

Now, the beauty of 2024-Alclad is that it polishes nicely and that it is quite strong. Although nearly as strong, the 6061 and 5052 alloys do not polish as easily or hold a polish as long.

The third advantage is availability--3003 is easy to find anywhere. I've had less luck finding 2024 in stock.

The second advantage (the one that lead me to 3003) is the cost--less than half per pound than 2024, and even less than that for alclad, up to ten-x less than for the 2024-Alclad coil-sheet from AirParts (although for aircraft, there's no substitute for 2024!). So for much less $$$, a skin could be replaced with 3003 alloy--a nearly pure alloy (98.8% Al & 1.2% Mn) which also retains an extremently bright polish. For example, tread-bright plates are made from this alloy. In fact, I cannot tell the difference color-wise between 3003 and alclad (1100 over 2024).

The advantage of this is that it is polishable aluminum all the way through--not just the clad layer. Therefore sratches and other issues can be buffed polished out no matter how deep the scratch.

The disadvantage is of course strength. However, because the modulus of elasticity (how much force required to produce a given deformation up to the yield point) is about the same for all aluminum alloys, this lack in strength can be made up for by using a thicker sheet--0.040 or 0.050. The stiffness of this (the bending moment of inertia), proportional to the thickness squared, ends up being 156% to 220% that of a 0.032" sheet--resulting in a stiffer, harder to bend panel.

The only issue remaining seems to be the tear-out strength of the rivet holes. Since in the many "popped" rivets I have seen have shown no deformation to the hole, and pure aluminum is still much softer than 3003, I am *almost willing to bet that this isn't a problem. In fact, the only place I've found structural problems have been in the frames, which appear to be made from 6063 architectural alloy--much stronger.

But before I make this decision, I wanted to find out how many out there have experimented with different alloys and thicknesses for the skin.

Thanks, and I look forward to you alls input!

-JP
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Old 07-08-2009, 06:39 PM   #2
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Depth

"The advantage of this is that it is polishable aluminum all the way through--not just the clad layer. Therefore sratches and other issues can be buffed polished out no matter how deep the scratch."

Wrong.
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Old 07-08-2009, 06:46 PM   #3
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Quote:
Originally Posted by Melody Ranch View Post
"The advantage of this is that it is polishable aluminum all the way through--not just the clad layer. Therefore sratches and other issues can be buffed polished out no matter how deep the scratch."

Wrong.
Please elaborate

I have buffed and polished out scratches in 3003 (starting with a heavy grit) in the past, and had no difficulty except for patience. What's wrong with that? I said it because I done it
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Old 07-08-2009, 08:43 PM   #4
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2024 is a bread and butter alloy used by aircraft makers. It yields at around 40-45ksi and has decent fatigue properties.

7075 is also an oldie but goodie that is much stronger; yield is around 70ksi,but it fatigues badly.

7050 is one of the new wonder alloys...I say new...but it's really about 15 years old. But you get the strength of 7075 and the fatigue resistance of 2000 series.

6061 is a nice alloy; about a 30ksi yield but it's more corrosion resistant thatn either 2000 series or 7000 series.

3000 series is fairly similar to the 6000. It's not as strong as the 2000 series, but it's got decent corrosion resistance.

OK, so the body of your Airstream is really not a monocoque structure (no matter how much marketing might suggest otherwise) and it sees very little load. You don't need the strength of 2000 series aluminum, much less 7000 series.

I would look at corrosion resistance. I believe the OEM thickness is around .032, but don't take that as gospel. You could use .040 7000 series and really build a tank. But moneywise, I think you'd be fine using 6061 or maybe a 3000 series.

That being said, 2024 is good medicine. I'm going to build my plane out of it. But it's pricey and you don't need the strength of it for what you're doing. But if you can get it, go for it.

take care,
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Old 07-09-2009, 12:43 PM   #5
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Thanks Jim!

Right now, I'm going for shiny, maintainable and affordable.

But for an aircraft, I too would never stray from 2024 for skins and 7075 for machined parts.

Now its just a matter of finding a supplier who sells sheets in 16 foot lengths. Most I find are limited to 10-ft lengths. The exception being Ryerson metals who will sell any length, but with a 1000-lb minimum (at about 1.50/lb shipped). Since I'd like to keep the side in a single sheet, I may bite the bullet and buy the sheet lengths needed from airparts.
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Old 07-09-2009, 06:22 PM   #6
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Hello all,

I'm new to the forum. It's nice to see such a good group of folks here.

I'd just like to toss in my 2 cents on this one. I earn a living as a pilot but I have a good 8 years of aircraft maintenance experience including extensive sheet metal work from 93 to about 2001.

Some of the other guys on here can tell you more about the different alloys than I can. But what I can tell you is this:

2024 T3, when dealing with .032 (or thereabouts) is really nice to work with. It bends reasonably well, it drills well, and most importantly imho it rivets well. Softer alloys can dent easily if you aren't careful when riveting. Harder alloys don't bend worth a snot. Maybe it's because most of my work was done in 2024 T3 but that would be my first choice for material.
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Old 07-10-2009, 10:01 AM   #7
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I'd love to hear more about your sheet metal experience--that's what I'm trying to gain. I've worked alot with aluminum (sounding rockets, airships, and lightweight structures), but my experience is limited to machining, welding, bending, and brazing.

In your experience have you ever done rolled edges (where a flap, say 1/4" or 1/2") is folded over flat to make a cleaner, stiffer, and safer (in terms of cuts) edge? I'd really like to learn how to do that without using a brake.
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Old 07-10-2009, 12:17 PM   #8
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I've done aircraft sheet metal since 1975. Everything you are proposing is doable but replacing the exterior skin with 3003 from the 2024-T3 is going to produce less then steller results. At a mimimun you should use the 6061-T6. The 3003 is so much softer then the TEMPERED 2024 that even with minor pressure, wear and tear, and the riveting process, the 3003 is going to dent, distort and generally look like S%#T in short order. save the untempered alloys for the belly skin etc. Folding the edge if metal over is called Hemming and really does require a brake to look professional. It cannot be done with 2024-T3 unless the aluminum is annealed first.
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Old 07-12-2009, 08:53 PM   #9
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I just completed a shell off floor replacement on my 1950 Liner. I have recently purchased 1 4'x12'x.025" and 1 4'x12'x.032". The .025 for misc repairs, wraps, c-channel etc. The .032 for an exterior skin replacement on the front lower skin. The cost was somewhat high (about $385 for the both) but what the way I see it I want to use the same material as the original for looks and strength. So far I found both materials great to work with. Bends and rivets well and looks great. I only plan on doing these repairs once so the cost of replacement is negligible. I plan on replacing all the interior skins for a custom look. I will be using a .025 thick material, same as the original but will go with a brushed aluminum surface. I don't know what it is called. Any clues?
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Old 07-12-2009, 09:35 PM   #10
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Old 07-12-2009, 10:29 PM   #11
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Yeah, so what is the proper Nomenclature?
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Old 07-12-2009, 10:45 PM   #12
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By the way, how do you guys get to be Rivet Members/Maters designation under your user name?
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Old 07-15-2009, 08:38 AM   #13
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Capntom,

The more you post, the more rivets you get.

It takes 500 posts to reach Rivet Master Status.

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Old 07-22-2009, 12:27 AM   #14
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Getting back to alloys, what is the type, thickness etc. of the alloy David Winick used on his 50 Flying cloud remodel? I would like to use this in my remodel, I'm new to AS and don't know all the differences and such. I like that brushed or sanded look. What is is that?
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