Numerical simulation of solidification of liquid aluminum alloy flowing on cooling slope N. K. KUND, P. DUTTA National Facility for Semisolid Forming, Department of Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India Received 6 July 2010; accepted 30 December 2010 Abstract: Preparation of semisolid slurry using a cooling slope is increasingly becoming popular, primarily because of the simplicity in design and ease control of the process. In this process, liquid alloy is poured down an inclined surface which is cooled from underneath. The cooling enables partial solidification and the incline provides the necessary shear for producing semisolid slurry. However, the final microstructure of the ingot depends on several process parameters such as cooling rate, incline angle of the cooling slope, length of the slope and initial melt superheat. In this work, a CFD model using volume of fluid (VOF) method for simulating flow along the cooling slope was presented. Equations for conservation of mass, momentum, energy and species were solved to predict hydrodynamic and thermal behavior, in addition to predicting solid fraction distribution and macrosegregation. Solidification was modeled using an enthalpy approach and a volume averaged technique for the different phases. The mushy region was modeled as a multi-layered porous medium consisting of fixed columnar dendrites and mobile equiaxed/fragmented grains. The alloy chosen for the study was aluminum alloy A356, for which adequate experimental data were available in the literature. The effects of two key process parameters, namely the slope angle and the pouring temperature, on temperature distribution, velocity distribution and macrosegregation were also studied. Key words: simulation; cooling slope; slurry; solidification; A356 Al alloy; semi-solid 1 Introduction Semisolid metal processing uses solid–liquid slurries containing fine and globular solid particles uniformly distributed in a liquid matrix, which can be handled as a solid and flow like a liquid[1−3] when sheared during the forming or injection process. In the recent years, many methods have been introduced for the production of semisolid slurries since it is scientifically sound and industrially viable with such preferred microstructures called thixotropic microstructures as feedstock materials. These methods can be divided into two groups[4−5]: 1) Methods which use melt agitation such as stir cast, electromagnetic stirring, mechanical or ultrasonic vibration and inclined plates; 2) Methods without melt agitation such as low pouring temperature and partial remelting, stress-induced and melt-activated (SIMA) process and addition of chemical refiners. Among several methods developed to produce such feedstock, magnetohydrodynamic (MHD) stirring is the most popular. This method uses shear forces by applying a rotating electromagnetic field to a solidifying liquid alloy in a conventional continuous die caster machine. In spite of its attributes, MHD stirring has some problems such as restriction in the size and morphology of primary solid phases and relatively non-uniform microstructures in the radial direction of produced ingots[4−5]. Thus, simple processes with reduced equipment and inhomogeneity in the final microstructure are required to overcome these problems. One such process that needs very low equipment investment and running costs is the cooling slope[6, 7−11]. In this method, the molten alloy with a superheat temperature is poured on a cooling slope. Solid columnar dendrites formed at the contact between the melt and the cooling slope, are broken into refined and globular microstructure as a result of shear stress due to gravity force and melt flow inertia. In this method, various parameters such as superheat temperature, cooling slope length and angle, can affect the final microstructure. HAGA and SUZUKI[12] experimentally studied the Corresponding author: P. DUTTA; Tel: +91-80-23604536; E-mail: pradip@mecheng.iisc.ernet.in Trans. Nonferrous Met. Soc. China 20(2010) s898-s905