If you want to cut thick aluminum fast and cleanly then you need to get a Sawzall Saw. these small electric handheld things are powerful. i once had a friend who literally gutted a washing machine into pieces, and sawed the motor in half!
you can find one on ebay for around 75.00 dollars. although if you don't have to saw a house in half afterwards i would just settle with a hacksaw or a dremmel.