Hi, square tube has little torsional strength without the perforations so you would not want to do what has been done in the image.
Frames are made from two different types of aluminum. (1) self hardening/7005 (2) must be heat treated /6061. The easiest and most practical way is to use a Easton 7005 kit. This has all the materials you will need to construct a frame. After welding (with special alloy wire) you will need to heat the frame for several hours (pizza oven) to properly harden it. If you choose to use 6061 you will need to the related parts like bottom bracket shell etc. and then solution harden the whole frame at a very high temperature. You can use recycled materials but aluminum is extremely difficult to weld and parts become contaminated with oil and paint making matters far worse. I am not sure what a MMA welder is but you must use a tungsten electrode shielded with argon gas. Wire fed machines won't work and will ruin your materials.
It's very difficult to produce an safe and ridable aluminum frame. Some would say no matter what you do you will still be better off with a 531 frame.
Last edited by ftwelder; 06-09-10 at 05:26 AM.