Following Roberts comment I agree. If aluminium is being used then there is only really one process that will work well if using electric, TIG ! AC TIG ! I recently bought a cheapish machine that has worked well and depending on what extras you add will do TIG, MIG and MMA at up to a CLAIMED 250A !This machine also claims to need 28A at 240V but is supplied with a 13A plug that does NOT even get warm when running at a setting of 250A ! Alli can be welded using MMA but is is messy and rods are expensive. If you use TIG or MIG you will need a supply of ARGON gas and unless you are a skilled welder you will need some time to get the hang of it. Working on 1/4″thick material I needed the claimed 250A. It was a ROHM 250 WSME. Noel.
PS If you go for TIG then avoid a scratch start type, go for high frequency start, the former will work but soon gets tiresome to use. N