Anon wrote here
My generic casting aluminum comes from dead lawnmowers and other small engines, and I think there’s the head off a car engine in there too. I have a lot more 6061 (a couple hundred pounds, actually) which isn’t so nice to cast, but machines beautifully once it’s heat treated. 6061 + 7% Si is better for casting, but still not as good as a real alloy. I have some Mn and Mg to whip up a batch of A535, which is supposed to have excellent castability and machinability without heat treatment (only moderate strength, though), but I need to source some pure Al (wire or something) for it.