I have cut aluminum up to 5/16" with my scroll saw. I use regular blades, just go nice and slow. The blades do get dull faster then with wood.
When I cut metal I sandwich it between two pieces of wood (1/8" or 1/4" ply usually, what ever I have the most of at the time) It really helps control cutting to have the wood. The metal likes to bend and will pinch the blade, get stuck under the table or just deform if you don't have the wood to back it up. This is especially true for thinner metals, but the thicker pieces can do it also.
Depending on what the piece is I would use a #5 or #7 blade for 3/16" aluminum.