Macrosegregation in dissimilar-metal fusion welding

Solute segregation across a weld between two dissimilar metals or alloys has long been recognized, but fundamental understanding is still lacking. Two macrosegregation mechanisms were proposed based on the liquidus temperature of the bulk weld metal TLW relative to those of metal 1 (or alloy 1) TL1 and metal 2 (or alloy 2) TL2. A “peninsula” of an unmixed metal 1 can form if TLW < TL1, while a “beach” of unmixed metal 2 irregular in shape can form if TLW > TL2. The mechanisms were verified in Cu-to-steel arc welding. The bulk weld metal showed a layered structure caused by undercooling of the bulk weld pool into a metastable miscibility gap in the Cu-Fe phase diagram. These findings were used to explain macrosegregation observed in laser- and electron-beam welding of Cu to steel or stainless steel.587