There are few 20+ minute videos that I've watched that haven't had me reaching to see if I could skip over some fluff. This one had my complete attention for all 23 minutes. Guncraft101 takes five pounds of saved aluminum cans and recycles them by melting and casting an AR-15 lower.
I've got to say his PPE (personal protection equipment) made me cringe a little, but that's the only thing I can be critical of. Upper arm-length, heavy, leather gloves combined with shorts and bare legs while pouring molten metal is enough to make me cringe. The rest of it is great stuff to know.
That said, I have to wonder if the metal would be useful for most things. When you see things saying they're made from "Aircraft Aluminum" or an alloy like 6061-T6 or 7075, that's a specific recipe for alloying elements in specific proportions, and T6 is a specific heat treatment. If I took a pound of 6061-T6 cutoffs and melted those down, instead of soda cans, I wouldn't end up with 6061-T6. All metals are like this, really. Steel, brass, aluminum, titanium or whatever, the properties you see depend on the ingredients (alloy) and how they're treated. Anyone who has taken the mechanical engineering classes on materials has seen something like this iron/carbon phase diagram. The different colors code for different microstructures in the steel, the temperatures and concentrations of carbon that lead to their formations. There are similar curves for aluminum and its main alloying additions - silicon and magnesium in 6061 or zinc and magnesium in 7075, for example.
I've never done casting, but I've been collecting aluminum scraps for a few years now, and have a couple of large buckets full of them (they're from 34 pound buckets of kitty litter), and I could start putting soda cans in the mix at any time. This is climbing my list slowly.