I did some welding on ali using a butter mig welder, an machine mart argon bottle and ali wire.
the control was good, although i had to set the welder to spot weld as the small argon bottle couldnt keep up with the flow rate of gas to the nozzle head.
The weld turned out ok, not beautiful to look at but i achieved welding up 2 pieces of 2mm thick ali 6inches long.
What i did find was that the ali needed to be kept cool though and one piece was clamped.
I would love to get an ac tig though as its a wonderful set up, for welding any metal.