Coarsening of dendrites occurs when heat removal drops suddenly after the formation of solid shell. This change in heat extraction can be caused either by slow casting speed or external disturbance in cooling system. Even if the increase in alloying elements favor coarsening, cooling rate determines the final dendrite arm spacing. Formation of the surface segregation is influenced by all process variables - directly on tin and phosphorous content and indirectly on cooling rate. Change in the dendritic length scale is required to obtain severe surface segregation. Coarsening is not sufficient condition alone to significantly reduce the elongation. Presence of the brittle constituent is also required. The cooling rate has more pronounced impact on dendrite arm spacing than on the segregation behavior. It was shown that in spite of the cooling rate, tin segregates in samples containing 8 or 10 wt.% Tin between the dendrites with the same final composition leading to formation of (α+δ) eutectoid. At low tin compositions brittle eutectoid does not form even with very high cooling rate.
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