Gentlemen,
We have had some success in making more durable weld connections in exhaust tubing of various materials. I chucked some scrap rigid copper 3/4" in the lathe and ground a HHS tool bit and didn't grind a chip breaker ledge on the bit. After some fussing, I was able to make some "copper wool" from the long strands of copper. We packed a bunch into a coupling point on an exhaust project after we tacked the joint in a couple of places. Then we finished the weld, and removed the copper heat sink. The exhaust repair is still in operation after three years of fairly hard use. We are talking about trying additional heat sink methods like wrapping the outside of the tubing with bare copper ground wire on either side of the joint to absorb even more heat.
Hope this helps some of your applications,
Happy Holidays and safe travels,
SAT