It really depends what you are attempting to weld. What thickness and what type of weld (butt joint, fillet, lap etc.). The norm for amps is 1 amp per .001”. So if you are attempting to weld 1/8” then you would need at least 125 amps. When I TIG alum. I usually run it hotter as in 150 amps. I like to get a puddle right away, so I start out hot and go fast. The key to aluminum is clean clean and more clean. Stainless brush only to get the oxidation off then finish up with acetone. MIGing aluminum can be a real pain, I have done it and do not like it. TIG is the way to go for alum. Just my .02 cents.
T.J.