Determination of heat transfer coefficients at metal–mold interface during horizontal unsteady-state directional solidification of Sn–Pb alloys

This paper presents a theoretical–experimental study of the metal–mold heat transfer coefficients during horizontal directional solidification of Sn–Pb hypoeutectic alloys (5 wt%Pb, 15 wt%Pb, 20 wt%Pb and 25 wt%Pb) in presence of thermo-solutal convection. A water-cooled solidification experimental apparatus has been developed, and specimens have been solidified under unsteady state heat flow conditions. Five computer guided thermocouples have been connected with the metal, and the time–temperature data have been recorded automatically. A numerical technique which compares theoretical and experimental thermal profiles is used for investigating the influence of solute content on hi values. This has permitted the evaluation of the variation of metal–mold heat transfer coefficients along the solidification of Sn–Pb alloys, as well as the analysis of the effects of thermo-solutal convection. The interfacial heat transfer coefficients of alloys studied are represented by equations which show the time dependence during the process. The experimental and calculated values have shown a very good agreement. A comparative analysis between the results of this work and those from the literature proposed to analyze the metal–mold heat transfer coefficients during upward and downward vertical solidification of Sn–Pb hypoeutectic alloys is conducted.

• The prediction of hi is of great interest for the design of the mechanical properties of solidified products.
• It is critical for industrial applications to understand the physical mechanisms which control the hi in solidification processes.
• Only a few studies have reported influences of thermo-solutal convection on hi and rares works have been undertaken to examine experimentally the hi during the horizontal unsteady-state directional solidification of alloys.
• The resulting thermo-solutal convection during the horizontal directional solidification influences significantly the hi.
• A comparative analysis between the results of this work and those from the literature proposed to analyze the hi during upward and downward vertical solidification of Sn–Pb alloys shows that the hi is strongly influenced on the direction of solidification with respect to gravity.