1 inch thick aluminum would require 1000 amps according to the AWS handbook which states 1 ampere per 0.001 inch thickness. That is with a balanced 50% positive/negative 60 hertz ac weld output with argon shielding gas. Increase the time at negative to 68% could reduce the amperage required by about 25%. That would be 750 amps needed. The new ac/dc inverters can achieve over 90% time at negative and the ac weld output frequency can be increased to 250 hertz. Take a piece of the aluminum to your welder supply house and try the biggest ac/dc inverter they have. Start out with the machines maximum ac weld output hertz, maximum amperage and 90% at negative time. Also ask to see argon 75/25 helium or 50/50 or 100% helium instead of argon. Suggestion would be to ask would GMAW be a better process with this thickness?

DCEN, 100% Helium, 2% tungsten. No preheat needed, 200- 300 amps does a fine job if you don't have a 1000 amp AC machine in your garage:)- Ted