2024 vs. 5052.... The debate

[nckysixx]

I'm about to pull the trigger on ordering aluminum to replace the interior skins. The jury seems out... I've got answers for both 2024 and 5052. 5052 is about half the price... So... What do I do?!

[LifeIsRiveting]

If you're not planning on polishing the interior skins then 5052 would probably be just fine (otherwise 2024 alclad is the obvious choice). 5052 is easy to work with and as you mentioned significantly cheaper and more readily available. However it is more of a medium strength alloy compared to the high strength of 2024 and would be more susceptible to dents for a given thickness. But dents and dings are less of a concern for interior skins when compared to the abuse that the outside sees. My vote it for 5052.

BTW, cool to see you are from Clovis, NM. That is where my parents met and I still have some family there.

[Cardinal283]

You might want to do some research before going with 5052. The biggest issue between 2024 and 5052 isn't "are you going to polish it or not" The shell is THE major structural component of the trailer not the frame. Going with a different alloy could lead to all kind of problems. Will the rivet holes tear out while you're bouncing down the road? Is 5052 as strong? Is it more or less brittle? Hardness? Temper? There's a reason the designers went with 2024 instead of a cheaper option. While 5052 is cheaper now, will it actually be cheaper in the long run if the material fails? Plus you're decreasing the value of your AS. If I was looking at buying someone's AS and found out they used 5052 to replace panels on the shell instead of 2024 I would walk away immediately. Just MHO. Just do some more research is all I'm saying as there's more to it than just polishing it or not.

[Mixter]

Originally Posted by Cardinal283

You might want to do some research before going with 5052. The biggest issue between 2024 and 5052 isn't "are you going to polish it or not" The shell is THE major structural component of the trailer not the frame. Going with a different alloy could lead to all kind of problems. Will the rivet holes tear out while you're bouncing down the road? Is 5052 as strong? Is it more or less brittle? Hardness? Temper? There's a reason the designers went with 2024 instead of a cheaper option. While 5052 is cheaper now, will it actually be cheaper in the long run if the material fails? Plus you're decreasing the value of your AS. If I was looking at buying someone's AS and found out they used 5052 to replace panels on the shell instead of 2024 I would walk away immediately. Just MHO. Just do some more research is all I'm saying as there's more to it than just polishing it or not.

Is the factory aluminum on interior 2024 T3??

[LifeIsRiveting]

@Mixter: I believe Colin Hyde has mentioned on The VAP that the interior skins are indeed 2024-T3. Seems like I have heard this other places as well…

@Cardinal: I agree that more research is a good suggestion and that the polishing question is not the main driver.

While there is no doubt that the inner skins can contribute to the overall structure it is obvious that the outer skin was designed to carry the majority of the load based on the significant number of solid rivets (shear strength of 350lbs for MS20470). We see this quite often with people towing around aluminum tents without catastrophic results. If the inner skins were meant to take significant load then they would have used a lot more pop rivets or else an alternate, more robust fastening method.
As is, the inner skins likely do little more than protect the wiring and insulation and allow interior anchoring of components. The small number of relatively weak pop rivets (120 lbs shear strength) dictate how much load can be transmitted to the inner skins. And as many Airstreamers know, pop rivets are the weak link, especially as subfloors rot and fail.

As far as structural properties between the two alloys, compared to 2024….
Shear modulus is practically the same
Ultimate tensile strength of 5052 is approx.. 50%
Yield strength of 5052 is approx 66%

But…those few pop rivets will continue to be the weakest link. My $0.02 is that you will not encounter any structural problems or inner skin failure by substituting 5052. I'm Hoping Aerowood will chime in as well.

-Jared

[Cardinal283]

For some reason I didn't notice that we were discussing interior skins when I read the original post. In which case it is not as big of a deal as with the exterior skins. However, as discussed in other posts regarding interior skins.... The interior skins do not carry the load like the exterior skins do. Hence as you pointed out the lack of a better rivet system. They do however prevent the ribs from twisting when there is a load applied to them. Once the ribs twist they lose all strength and a downward load can buckle the exterior skin like foil. And the rivets will not have failed. There are several examples on the forum of owners up north who had their interior skins out over the winter with a foot or two of snow on the roof and the roof folds in. It does beg the question though "why doesn't Airstream use 5052 on the interior?". Personally I'm an advocate for going back the way they designed it. You can't go wrong that way. When you change something like that you run the risk of some unforeseen circumstances ruining you day just because you saved a few hundred dollars.

[Cardinal283]

But for what it's worth, Jared. I doubt one would have problems using 5052 on the interior. On my trailer though I'm not risking it.

[truckasaurus]

There have been plenty of different alloys used on airstream interior skins Mine has quite the mix. On my rebuild I almost certainly will not be using 2024 in the interior I was a licensed aircraft structures engineer for a period and feel 2024 is not even close to being necessary. If they cost the same I would use it but they don't

[HiHoAgRV]

I've got over 20,000 miles on my shell off rebuilt utilizing .025 3003 for the interior. It's bare, shined but not polished. The only thing I wish I'd done different (and I have in a subsequent trailer) was using .032, it doesn't ding as easily.

Like mentioned, no issues with the alloy, only 2 rivets have hit the ejector button somewhere along the journey (and this is the trailer that I used a Prodex layer over the ribs as a thermal break)

[Belegedhel]

Originally Posted by nckysixx

I'm about to pull the trigger on ordering aluminum to replace the interior skins. The jury seems out... I've got answers for both 2024 and 5052. 5052 is about half the price... So... What do I do?!

Well, if the jury is out, then perhaps they haven't had any real evidence presented to them. Have a look at the attached, which I will call Exhibit A. This is Airstream's history of aluminum. It seems that your 77 falls possibly in the years that 6061 T6 was used as an exterior alloy, but more likely 3004 H18. So I'm thinking that replacing the interior with 2024 is way overkill unless you want the corrosion resistance of the Alclad, in which I say use a 6061 (or any other cheaper alloy) Alclad and still save money.

As for the structural strength of the interior material, may I suggest that you use .40 thickness, as you will end up with less ripples and a smoother look. I've said it before, and stand behind my earlier assertion, that the strength of the interior panels is limited by the miserable pop rivets that hold it in place, that are only placed 4-6 inches apart, not by the strength of the material, be it 5052 or titanium.

If you are planning on putting in raw shiny aluminum, then prepare yourself for every fingerprint to turn into a permanent corrosion spot. I have yet to hear of anyone who has found a coating that looks good and will stay in place. You can buy the pre-coated sheets just like the factory uses, but if you think the 2024 T3 Alclad is expensive, hold onto your hat.

good luck!