Interactions between alumina particles, aluminum alloys, and their inclusions during aluminum filtration before casting.

摘要

This project was undertaken to study the interactions between alumina particles, aluminum alloys, and its inclusions under liquid aluminum flow conditions. The objective was to develop a test method which can simulate the conditions similar to those in the aluminum filtration process and to evaluate the interactions taking place between various types of alumina samples, aluminum alloys, and its inclusions. With this test method, it was aimed to determine how various alumina types behave under flow conditions during the filtration process.;The experiments with various liquid Mg-Al alloys (0, 2, 5, and 7 wt% Mg) were conducted for different residence times (from 6 hours to 168 hours) using the above experimental systems. The effects of the liquid aluminum alloy velocity, the temperature of the melt, the physical (apparent porosity, surface roughness, etc.) and chemical (impurity content such as Na2O, SiO 2, etc.) properties of alumina samples on the extent of aluminum alloy/alumina interfacial reactions were determined.;The samples obtained from aluminum-alumina experiments were analyzed by using the optical microscope, the scanning electron microscope -- energy dispersive X-ray spectroscopy (SEM-EDX), the micro probe SEM, and X-ray diffraction (XRD). The results indicate that the chemical reactions between high density pure alpha-alumina and molten Mg-Al alloys are not fast; however, the presence of impurities (such as Na2O as beta alumina phase) and the porous structure in alumina increase the extent of reactions significantly. Na2O rich phase (beta alumina) found in all commercial alumina grades seems to be one of the most important contributors for the spontaneous reactions of Mg vapor with alumina, even at the shortest residence time. The major reaction product was found to be Mg-spinel. The thermodynamic analysis indicated the same tendency.;Chemical interactions between alumina, aluminum alloys, and its inclusions were investigated under both static and dynamic flow conditions. In order to study these interactions under dynamic flow conditions, a knowledge of the velocity field in the vicinity of the alumina particles is necessary. In this project, two unique experimental systems which can simulate the flow condition of the industrial bed were designed and built. A mathematical model was also developed to predict the flow field around the particles in the experimental system. The mathematical model was validated by comparing the predictions with the results from a physical model in which water was used as the fluid. The mathematical model was then used to conduct parametric studies to determine the design and operational parameters for the actual experimental system in which the tests were carried out. This allowed the generation of a flow field similar to that of the industrial filter.