Details on Aluminium types::

• 6061 - All purpose, very strong and used for plates, housings, axles, pretty much anything. Good machinability

• 2024 - Stronger than 6061 for axles and standoffs. As strong as a mild steel

• 7075 - Extremely strong aluminum alloy, used for axles, gears, sprockets. Common on aircraft

• 5052 - Easy to use in bending applications and is also extremely easy to weld

Aluminium Tubing

Gusset material can be cut on the bandsaw using a 20-24 tooth per inch Bi-metal blade running at a slow speed, under 200 feet per minute to keep heat down.

Detailed discussion here of Aluminium stock: http://www.chiefdelphi.com/forums/showthread.php?t=122270&page=4

Survey of fabrication techniques: http://mort11.org/static/summersessions/Construction,%20Materials,%20Fabrication.pptx