Ab-initio Predictions of Interfacial Heat Flows during the High Speed Casting of Liquid Metals in Near Net Shape Casting Operations

摘要

When metals are cast into solid shapes, the quality of the solid casting depends on many things, but heat flow management is a critical factor. It is relatively easy to predict heat flows through the liquid metal, and the solid mould, but heat flows through the interconnecting interface have been much more difficult to quantify. In the present work, following a review of our progress up to date on near net shape casting, the approach is to model this interfacial resistance from first principles. By conducting experiments in which liquid aluminum is cast at high speed (～0.5 m/s), onto a copper substrate, fitted with extremely sensitive embedded thermocouples, heat fluxes from the first moments of metal contact, to final freezing of the strip, have been measured. Similarly, by using a 3D profilometer that is able to rapidly characterize and quantify the surface topography of a substrate, to ±1μm, one can have the necessary data to mathematically model the transfer of heat from the overlaying metal, through the interfacial layer, into the copper substrate. The thermal model briefly described, makes the assumption of point contact between pyramidal peaks of the metal substrate and molten metal, with gas pockets trapped in the "valleys" of the substrate, through which heat must be transferred by conduction. Ab-initio instantaneous heat fluxes predicted in this way proved to be in good agreement with those measured, provided adjustments were made for expansion of the "air gap".