Leo, I'm speaking of welds between two different metals. Assume for the sake of argument that we're making a butt weld between two 1/8 plates of metals A and B. (Assuming that it is in fact possible to weld these metals together.)
At some point, the A plate becomes a B one, because they're all molten together at the weld joint. As I understand Roy, there is a sharply deliniated boundary between metal A and the A/B alloy that is the weld bead, and then another boundary between the alloy and metal B.
If there is such a boundary, then it seems like the structure of the joint is similar to that of a soldered one, even if the physical properties are quite different. Are the improved physical properties therefore the result of the inherent quality of the joint; that the alloy is simply better at bonding to metals A and B because it is an alloy of those metals? Or is it that the alloy is simply stronger than solder?
If not, then how does the joint differ metallurgically from a soldered one? Is the transition a more gradual one, where it is not quite possible to say where metal A ends and the alloy begins, because the crystals are interlaced?