You could cast the parts out of beer cans - absolutely true. The only problem in using that particular alloy of aluminum is that it is strain hardened, not heat treatable. FWIW, you can find the same type of alloy in huge, easy quantities by scarfing it off some aluminum siding from a house tear-down, or gutters in the local dump.
There are other alloys which you could find - like the aluminum used in crackcase housings off diesel engines, the pistons off diesel engines, etc. These alloys all exhibit better strength and casting properties than most of the other stuff you could find.
People would do well to think in terms of “Golly, the local auto wrecking yard is positively FILLED with metal... what *is* that metal in there?”
There’s quite a few very useful alloys that are very commonly available in a junk yard - if you know where to look. Axle shafts, transmission gears, pistons, crankcase castings, wheel castings, etc.
I could make some very strong aluminum parts from cat or Cummins aluminum pistons, wrist pins can be used for barrel making and connecting rods are perfect for milling trigger parts. I have a beautiful fixed blade knife made from nothing more than a welded chainsaw blade. i made my own knife thats like a bowie out of timken loader differential race, a bitch to hammer I tell you, 52100 steel I think it was.