Investigation of rapid directional solidification of Al-based immiscible alloys

The forces acting on the droplet in front of the S/L interface during the solidification of immiscible alloys have been analyzed. The dynamic criterion for the interaction mode between the droplet and solidification interface has been proposed. Combining experiment, the effect of the interaction between the S/L interface and the droplet on the microstructure development in the Al-Bi based immiscible alloy has been discussed. The results indicated that the small Bi-rich droplets were repelled and accumulated in front of the solidification interface due to the combined action of the interfacial repulsion and Marangoni migration. If the interface morphology is dendritic or cellular, the Bi-rich droplets with critical size are partially entrapped by the interface and form tadpole-type particles, while, the smaller Bi-rich droplets will be entrapped in the interdendrite and the Bi-rich particles distribute at the grain boundaries and the triple junctions after solidification.