I laughed when I read that the wire bunches up in the mig. Brought back memories ages spent re feeding the wire through the mig on many occasions, wasting half a roll of wire, and in the end welds that look like bird poo and just as strong as it.
Solder wont stick to Alluminium.
We used to use Quick steel or Knead It to fix the corroded water pump housings on our old postie bikes. If you cant get some of that just use Ariledite. Clean and scratch up the surface good so that it sticks and then whack it all back together to continue on riding.
Cheers Steve