I got an email about Al wheels that was not posted here, thought I'd
pass it along:

+ Be careful using Al wheels, some have magnesium in them,
+ and can flare up in your face. Try getting Al piston from any type
+ of engine. Lawnmower engines are also good Al material to use.

Unfortunately the author did not mention how to differentiate between
the two. One one of the Al pans that I've scrounged up, it says
"Al Si 12 (Cu)" on it, I'm guessing 12% Silicon and a little bit of
Copper.
I'll avoid wheels that ever say Mg on it (Magnesium). Mn is Manganese,
but I don't think that's commonly added.

Tom.
http://www.TomEberhard.com