[Andy A.]

My experience has been with inch square aluminum tubing with a 1/8th wall thickness. 6061 is the default alloy of choice for the majority of FIRST applications, tube or plate. It offers good strength characteristics while being weldable. It's also very common which increases your options for quantity and shape and decreases lead time. There are probably some places where other alloys would be better suited, but few where 6061 is a bad choice.

Welding will toast the heat treatment. I've seen very few clear cut cases of the joint failing because of this, but it's worth considering.

Polycarbonate can often be substituted in place of aluminum plate where stiffness is not critical. Both materials weigh about the same but the plastic is easy to worth with, non conductive, transparent to light and radio and a whole litany of other pros.

Plywood is another good substitute for aluminum in some cases. It is again easier to work with, non conductive and with quality wood very tough. It is cheaper and can be easily found. I've often used it to 'prototype' aluminum parts, only to find that the wood works perfectly well. It can quickly be replaced modified or glued back together if need be.

Just don't invest your team to heavily before the season starts. For all we know aluminum may be banned this coming season.

-Local