Need Any Welding advice?

I was going to ask JUST one question, before all panties got in a wad!
Stepson has a big bass boat. Other day, he found the "bracket", yes it is big , that holds the BIG outboard, was cracked. It is cast aluminum. I also noticed that it is not just bolted together but some of it is welded.
Aluminum stock trailers are mig welded. What is the system to weld this cast aluminum? Just curious.
I watched an alum. humongous house boat being built in Alaska on tv, they didn't have much trouble with using a mig spool gun set up, and it was bigger stuff, and a hell of a lot colder . ??????????