Formation mechanism of macrosegregation in dissimilar-filler welding of aluminum alloys

Dissimilar-filler welding is widely used for joining aluminum components. However, macrosegregation that will degrade the performance of the weld joint commonly occurs within the weld metal, because of the compositional difference between the filler and base metals. This study reports a new mechanism for the macrosegregation introduction during dissimilar-filler welding. Liquid segregation is induced in the weld pool owing to dynamic heterogeneous mixing between the filler and the base metal melts. In the front portion of the weld pool, heterogeneous mixing proceeds uninhibited owing to convection and the presence of a continuous heat source. However, away from this region, the temperature of the weld pool is significantly reduced, and solidification dominates heterogeneous mixing. If the heterogeneous mixing has none or only partially occurred, this liquid segregation is frozen into the weld metal to introduce macrosegregation. The mechanism elucidation will provide new insights into the improvement of weld joints.