I have a bunch of 3/8'' thick aluminum angle (2''x2'') and I'd like to make a brace like the butterfly brace. Any reason why this wouldn't work?

 

You tell me?

 

Should work fine as long as you get some triangulation in it. It may be a little heavier due to it being steel but will work just fine. I still need to do the same to mine so I will be interested to see some pics of it when you make it.