You need safety-silv 56 for this project..... Melts at about 1500°F....
Bronze filler melts at much lower temps... Bronze also doesn't wick down into the joint as well as silver does...Bronze does build up easily but it's not great at being a thin layer down inside the joint like you want....
Agree, very strong way way to assemble tubing. Here's some of my work on .035 wall steel tubing. My test joints were almost unbreakable.