The effects of melt overheating treatment on solidification of Pb-Bi alloys were studied from the viewpoint of liquid-liquid structure change (LLSC). Anomalous temperature dependence of internal friction, electrical resistivity, and entropy of liquid Pb-Bi alloys suggested that discontinuous LLSC occurred within about 520–740 °C, based on which the solidification experiments were carried out with different states of Pb-Bi melts. The results revealed that the LLSC affected the solidification behavior and microstructures significantly, that is, the enlarged undercooling, increased nucleation rate, and refined and improved morphologies were brought about when solidifying from the melt experienced LLSC. It is assumed that the LLSC changed the energy constitution of the melt system, and further affected the effective partition coefficient, thermodynamics, and kinetics of crystal growth, then finally altered the solidification behavior and solidified microstructures. This work brings a novel insight into the effect of melt overheating treatment on solidification, by which it could be more effective to manipulate melts.

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The electrical resistivity of the liquid Sb–10 wt-%Cu alloy as a function of temperature was measured using direct current four probe technique. In a relatively high temperature zone above the liquidus, the resistivity–temperature ( ρ – T ) curves of the melt change abnormally; moreover, the changing pattern in the first heating process is completely different from the ones in the subsequent heating and cooling cycles. Since resistivity is a structural sensitive parameter, these abnormal changes of ρ – T curves indicate that the temperature-induced liquid–liquid structure transitions (L-LSTs) probably occur in Sb–10 wt-%Cu melt, with some reversible characters. To explore the effects of the L-LST on the solidification behaviours and solidified microstructures of this alloy, solidification experiments were further carried out according to the temperature ranges with anomalous changes on ρ – T curves. Results show that after the melt experienced the L-LST, larger undercooling, shorter solidified time and much finer microstructures with differently microscopic patterns could be obtained.

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