Aluminum with a MIG is a trick even for an experienced welder. TIG is usually the answer for aluminum.
Now SS works well with MIG. 100% argon gass as I recall and change out the gun liner.
One of the difficulties with aluminum and MIG is shooting out the wire fron the gun. Then the aluminum looks like it is welding along perfectly when a 3" hole drops out. Having different gun feed liners is a must.
