Can we weld on aluminized or stainless tubing?

It seems to me that aftermarket systems use clamps because the average garage does not have inert gas welding equipment rather than concern over welding.

If the car in you avatar is the one that is to receive the new exhaust system, you may want to check routing of a dual system. The TB X-member on the passenger side is not notched for pipe clearance. Running a pipe underneath it usually results in a crushed pipe.