Multiphase Model of Semisolid Slurry Generation and Isothermal Holding During Cooling Slope Rheoprocessing of A356 Al Alloy PROSENJIT DAS, SUDIP K. SAMANTA, BISWANATH MONDAL, and PRADIP DUTTA In the present paper, we present an experimentally validated 3D multiphase and multiscale solidification model to understand the transport processes involved during slurry generation with a cooling slope. In this process, superheated liquid alloy is poured at the top of the cooling slope and allowed to flow along the slope under the influence of gravity. As the melt flows down the slope, it progressively loses its superheat, starts solidifying at the melt/slope interface with formation of solid crystals, and eventually exits the slope as semisolid slurry. In the present simulation, the three phases considered are the parent melt as the primary phase, and the solid grains and air as secondary phases. The air phase forms a definable air/liquid melt interface as the free surface. After exiting the slope, the slurry fills an isothermal holding bath maintained at the slope exit temperature, which promotes further globularization of microstructure. The outcomes of the present model include prediction of volume fractions of the three different phases considered, grain evolution, grain growth, size, sphericity and distribution of solid grains, temperature field, velocity field, macrosegregation and microsegregation. In addition, the model is found to be capable of making predictions of morphological evolution of primary grains at the onset of isothermal coarsening. The results obtained from the present simulations are validated by performing quantitative image analysis of micrographs of the rapidly oil-quenched semisolid slurry samples, collected from strategic locations along the slope and from the isothermal slurry holding bath. https://doi.org/10.1007/s11663-018-1211-1 Ó The Minerals, Metals & Materials Society and ASM International 2018 I. INTRODUCTION MODELING of semisolid processing of Al alloys is a multiphase and multiscale problem. Solid evolution and grain formation within the liquid melt during slurry generation is governed by mass, momentum, energy, and species transport. Such models should also include the physics of solid nucleation, grain growth, and species redistribution at the interface. Development of multi- phase solidification modeling was pioneered by Beckermann and coworkers [1–3] who have followed vol- ume-averaging approach to treat the liquid and solid phases as separated but highly coupled and interpene- trating continua. Subsequently, Ludwig and Wu have modified the nucleation model and heat, mass exchange terms [4–8] to study globular equiaxed solidification. In case of globular equiaxed solidification, solidified grains can be modeled as spheres, and their sizes can be expressed with a volume-averaged diameter, [4,5] which is also the approach followed in the present study. This is different from the earlier published reports by the present research group [9] in which a special enthalpy update scheme was used to solve multiphase solidification problems. There are several attempts to develop numerical model of cooling slope slurry production [10,11] ; however, these models are generally macroscopic in nature and do not provide deep insight into microscopic issues such as microstructural morphology of the growing primary Al grains, effect of increasing solid content on slurry viscosity, ripening-driven grain coarsening, and so on. Also, the above models are not accompanied by rigorous experimental validation. A brief overview on different slurry-generation techniques reported till date PROSENJIT DAS is with the Center for Advanced Materials Processing, CSIR-Central Mechanical Engineering Research Institute, Durgapur, 713209, India and also with the NNMT Group, CSIR- Central Mechanical Engineering Research Institute, Durgapur, 713209, India. SUDIP K. SAMANTA is with the NNMT Group, CSIR-Central Mechanical Engineering Research Institute. BISWANATH MONDAL is with the Center for Advanced Materials Processing, CSIR-Central Mechanical Engineering Research Institute. PRADIP DUTTA is with the Department of Mechanical Engineering, Indian Institute of Science, Bangalore, 560012, India. Contact e-mail: pradip@iisc.ac.in Manuscript submitted May 14, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS B