Interaction between L2 droplets and L1/L interface in solidifying Al–Bi immiscible alloy

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Using synchrotron radiography, we observed the advancing L1/L interface and its interaction with L2 droplets during directional solidification of the Al-10wt% Bi immiscible alloy. Five forces act upon L2 droplets in front of the L1/L interface. The repulsive force that pushes the droplets away from the interface is the largest force when the droplet radius (r) is smaller than 20.5µm, while Marangoni force is the largest one when 20.5µm <r<89µm. And the resultant force that is responsible for the pushing of the droplets is larger than the drag force when r<141.5µm, leading to upward movement of L2 droplets.