I am curious about what I need to know about MIG welding aluminum. I have an old (15+ years) Blue-Point MIG welder. At the moment I am unsure of it's output amperage (I forget and it's in the shop right now, but can't check it until later). It does run off 110V and input amperage is 20A. It's a "true" MIG system for use with shielding gas, not flux core wire. I typically weld thinner sheets of steel ranging from auto-body stuff to 1/8" thick plates and use an argon/co2 mix as the shielding gas (75% argon/25% CO2).

I searched for Mig Welding Aluminum and came up with no results which seemed strange that no one asked this before.... but what do I need to know about MIG welding aluminum compared to steel?

The application is pretty much the same as my previous steel jobs just in aluminum: thin sheet metal up to plates up to maybe .250" or possibly even thicker. A specific customer wants to know if I can weld some thick-walled aluminum tubing at right angles to each other. For steel, and I assume the aluminum, I would first notch out the end of one aluminum tube with large end mill or hole-saw to fit around the OD of the other tube, and bevel the edges of the notch for the weld to fill in.

My MIG welder will accommodate a spool of .030" aluminum welding wire, available from my local hardware store. So my questions are:

1) Should I use the same shielding gas? Argon/CO2
2) How much amperage will I need to weld aluminum? I know it's application dependent so use for example a 1.5" diameter aluminum tube with .125" thick wall welded as described above with the end of one tube being welded to the OD of another tube.
3) Is the "standard" welder polarity for use with steel welding with gas shielding work? I've heard that flux-core welders use a reverse polarity, but mine is not selectable. I might be willing to buy another welder if mine turned out to be unsuitable since it's not a great welder anyway.
4) Any special techniques I should know about?

Thanks for any and all help!