A mig welder can be used for aluminum (well some can) as long a you get a different welding material and you adjust the speed and current and running a different gas (not the argon/co2 mix, it is just argon (i think). I think you even need a different welding head (thingie).
It is probably not as durable as a tig weld, but that stands true for Mig vs Tig welding in general.