Simulation of thermos-solutal convection induced macrosegregation in a Sn-10%Pb alloy benchmark during columnar solidification

Abstract

Abstract:In order to investigate the effect of thermo-solutal convection on the formation of macrosegregation during columnar solidification, simulations with a liquid-columnar two phase model were carried out on a 2D rectangular benchmark of Sn-10%Pb alloy. The solidification direction in the benchmark is unidirectional: (1) downwards from top to bottom or (2) upwards from bottom to top. Thermal expansion coefficient, solutal expansion coefficient and liquid diffusion coefficient of the melt are found to be key factors influencing the final macrosegregation. The segregation range and distribution are also strongly influenced by the benchmark configurations, e.g. the solidifying direction (upwards or downwards) and boundary conditions, et al. The global macrosegregation range increases with the velocity magnitude of the melt during the process of solidification. IntroductionMacrosegregation is the inhomogeneous solute distribution at the scale of a casting and it is very sensitive to thermal-solutal convection [1]. It is important to understand the macrosegregation, and be able to model and control it because macrosegregation is usually detrimental for castings. Macrosegregation is mainly due to a combination of microsegregation and relative motion between liquid phase and solid phase [2][3][4][5]. The relative motion during the solidification is induced by different flow phenomena, for example, equiaxed sedimentation, thermo-solutal convection or feeding flow. In this study it is dedicated to illustrate the delicate mechanism of macrosegregation during solidification with the presence of thermal-solutal convection. This is also an important topic in the annual solidification course in Swiss Federal Institute of Technology of Lausanne (EPFL) [4,6]. There are lots of works carried out on lateral solidification benchmark [7][8][9][10][11] while the investigation on the vertical-directional solidification is not sufficient. In order to investigate the effect of thermo-solutal convection on the formation of macrosegregation during vertical-unidirectional solidification, a series of simulations with a liquid-columnar two phase model were carried out on 2D rectangular benchmark of Sn-10%Pb alloy. The aim of this paper is to explore the effect of thermo-solutal convection on macrosegregation in detail.