For TIG welding aluminum the best types of machines are the inverter types. TIG welding Al requires AC. (DC electrode negative which is almost always used for steels doesn't work with Al since it lacks cleaning action.) For welding 1mm Al I'd estimate 17-30 amps or less, depending on your skill and travel speed. 2.5 mm I'd say around 50 amps. Beneficial features on a TIG welding inverter, when welding Al are: -"square wave" AC -high frequency generator -wave balance control -high frequency intensity control -AC main frequency control. Square wave improves arc performance and also reduces tungsten erosion. High frequency creates improved cleaning action and allows for touch-free starts. Wave balance allows the welder to adjust between a more strongly penetrating arc for new joints on clean materials, and better cleaning but less penetration for weld repairs on existing, dirty aluminum. HF intensity improves weld appearance and can help mitigate erratic arc and poor starting problems. AC frequency control partially adjusts the width and focus of the arc, and can help with penetration.