From Applied Science.
This unusual sheet metal is made of hundreds of nano scale layers of aluminum and nickel. A spark initiates a self-propagating reaction that creates NiAl compound, and lots of heat! This material is used to solder items so fast that the base material doesn’t have time to draw heat away from the joint. The technical data sheet indicates that this process is fluxless, and I suspect trying to include flux would cause rapid gas expansion that would blow the solder joint apart. I’m not sure how the solder wets the surface without flux.