Check with a welding shop and ask for true silver solder or silver braze. Or you can braze the parts with bronze welding rod. The solders used for plumbing, electrical, etc. are low melting temp and won't last 2 minutes on an exhaust system. There is also a silver solder called "Sta-Brite" that has a small percentage of silver in it, but it is also low melting temp and won't work either.

The brazing will require a hotter torch than the common plumbers propane torch as well...

AV8TOR