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I love ejection seats and the flying contraptions they usually reside in. In fact, I like them so much that I want to make my own, despite my profound lack of training and inexperience with mechanical engineering in general. After doing a little research into the materials for my ejection seat, I found a large collection of aluminum alloys to choose from. Some are fairly simple to eliminate like the 1000, 2000, and 3000 series. However, between the various grades in the 5000 and 6000 series, I have a lot more trouble.

I read that 6061 is the most common alloy for reasons of weldability, corrosion resistance and a few properties. Also, I intend to rivet the chair together because that's what I see in my detailed source pictures though I have a little experience with TIG welding so that may be an option too.

In the benign environment of my office, will it really matter which alloy I pick? Can I just use common 6061 sheet or is there a better, cheaper alternative?

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    $\begingroup$ You want an ejection seat for your office? $\endgroup$ – Wasabi Mar 12 '16 at 2:18
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    $\begingroup$ @Wasabi Yep. So, should I ever need to, I can look my boss dead in the eye, with a straight face and say "I quit" and pull the ejection handles. $\endgroup$ – Green Mar 12 '16 at 2:21
  • $\begingroup$ This is for my home office though. $\endgroup$ – Green Mar 12 '16 at 2:22
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    $\begingroup$ You'll probably want to go with the rivets for this. TIG welding aluminum is rather more difficult than steel due to the high thermal conductivity, low melting point and high reactivity. You'd need to get a fair bit of practice and understand how to prep materials correctly in order to get welds that are strong and look reasonably good. $\endgroup$ – Dan Mar 12 '16 at 4:36
  • $\begingroup$ @Dan Agreed. The loss of strength in welded aluminum and the difficulty in doing so pushes me strongly towards rivets. I don't want to fight with aluminum oxide if I don't have to. $\endgroup$ – Green Mar 12 '16 at 5:33
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In your situation (as long as you don't actually intend to use the thing!) 6061-T6 will be just fine. The main reason to pick it is that many more product forms are available in it than most other alloys, and it is relatively inexpensive. It is one of the strongest among the weldable aluminum alloys and very easy to machine (as most aluminum is.)

The one big exception is if any of your parts require you to bend the aluminum over a relatively sharp corner. 6061 will generally crack in this case, and 5052 is the most readily available alternative that bends a little better.

Do keep in mind that some or all of the parts in your source material are probably cast or forged aluminum, which you will not be able to visually replicate by machining from solid aluminum.

6061-T6 is heat treated, so if you do TIG weld it be aware that you decrease it's strength by more than 50%, even if you make a perfect weld which is not easy on aluminum. After welding it will be 6061-O, rather than 6061-T6 in the heat effected zone. Again, since you're just making a replica chair, this shouldn't be an issue.

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  • $\begingroup$ That's incredibly helpful, thank you. I don't intend to strap a bomb to this chair, this is just for my own satisfaction. The heads up on bending is helpful, I'll go look up the appropriate tables. There are some wicked looking curves that I will just have to approximate. $\endgroup$ – Green Mar 12 '16 at 2:32
  • $\begingroup$ For those who may come after, this is a bend radius table I found: americanmachinetools.com/bend_radius.htm $\endgroup$ – Green Mar 12 '16 at 4:20
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As an aside, if you want to bend and play with it. Here's a tip. Get a pot of soap, a gas blow torch and sit by a bath. Smear the part with soap. Heat with the blow torch until the soap turns black, then drop it in the cold bath.

Depending on your air temperature you've now got a few hours to bend it to your desired shape. once down leave it in the airing cupboard or somewhere else nice and toasty for a day or so. The alloy will then regain it's stiffness.

What you've done is melt the nickel and copper crystalline structures within the aluminium. Now it will fell, bend and act like pure simple aluminium. Once you give it time the copper and nickel will reform the internal structure and you're done.

Welcome to home heat treatment. it's exactly the same way I saw piper making skin panels in Vero Beach. Heat the cut to shape skin panels, drop them in a tank then bend them onto the back and clico rivet. Then they put the parts out in the Florida sunshine. Job done.

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