[Dick Linn]

First, make sure whoever welds it is experienced in welding thin Aluminum! Second, make sure that you know which alloy is being used for the tubes, and use the proper filler metal for that alloy. Some alloys are virtually unweldable, some depend highly on the exact filler alloy and others are not too finicky. Check out the sites of the major welder manufacturers like Licoln (do a Google search on Aluminum welding - Licoln should pop up to the top).

Is there any way you can use gusset or reinforcing plates and rivet/pop-rivet/screw the sections together? You will note that aircraft and monocoque racing cars are typically held together this way, not welded. For that matter, steel buildings are often bolted/riveted together. This year, our chassis is 1" x 1" square tube held together with #10-32 alloy allen-head screws and gusset plates/angle brackets.

If you are using heat-treated or work-hardened Aluminum, welding will soften it and you will lose structural strength. You can, with difficulty, heat treat some alloys (have a 1000 degree oven?). You cannot work-harden a complicated construction (unless it bends and you beat it back in shape.)

There are some interesting new techniques like "friction stir welding" that may show up in future aircraft but I'd stick with something simple, like riveting, if at all possible. That, or weld, then reinforce as necessary.