I also remember seeing thin sheet metals (back in the 1930's) being welded together using a powder burn process where you used a flux (plumbing pipe flux) mixed with bonding metal powder (same metal as the sheets) and magnesium powder.
The mix would have to be experimented with to get it right. (not to burn too hot or too cold)
But you use the paste between the seems of the sheet metal and ignite it with a torch. The magnesium powder flares and burns melting the powdered metal and "welding" the two sheets together. (it is not a clean weld but it works)
You just have to be very careful. a little magnesium goes a long way and can easily hurt you when it flares. (remember grade 12 science?)