ABSTRACT
The thermo-physical and physical properties of the liquid and solid phases are critical components in casting simulations. Such properties include the fraction solid transformed, enthalpy release, thermal conductivity, volume and density, all as a function of temperature. Due to the difficulty in experimentally determining such properties at solidification temperatures, little information exists for multi-component alloys. As part of the development of a new computer programme for modelling of materials properties, JMatPro, extensive work has been carried out on the development of sound, physically based models for these properties. Wide-ranging results have previously been presented for Fe, Ni, Ti, Al and Mg-based alloys. The purpose of the present paper is to look at how changes in composition can substantially affect properties of multicomponent alloys during solidification and further demonstrate how properties of the liquid can substantially vary in the mushy zone.
1. INTRODUCTION
In solidification modelling, there is often a requirement for high quality information concerning thermo-physical and physical properties. Some properties have been measured for specific alloys, but the number of alloys where information is available is limited. Furthermore, the information may be incomplete, in that not all properties measured and, sometimes, disparate information from a variety of sources is used to build up the data for a specific alloy. The latter method can inherit inconsistency as the composition of the alloys used to build up the property database may not be the same and various important temperatures (i.e. solidus, invariant reactions) may differ between the alloys. Furthermore, there may be variations linked to different experimental conditions.
An advantage of using a calculation route to provide properties is that the calculation is internally self-consistent. It can therefore provide extensive information on how the properties of an alloy may change within a specification range as well as providing detailed information on the properties of the liquid phase in the mushy zone. Furthermore, it will be made clear from the examples presented in this paper that properties experimentally measured in the fully liquid state cannot be extrapolated into the mushy zone with any confidence. Such detail is important in modelling defect formation and is something that is usually beyond the capability of measurement.
The self-consistent calculation of thermo-physical and physical properties is further potentially important in determining unknown properties, such as the heat transfer coefficient at the ingot/mold interface, through inverse modelling. In this case, a full set of consistently calculated properties may lead to a more rigorous estimate and understanding of this property.
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