Mold Filling Simulation and Interfacial Heat Transfer Coefficient Measurement for the Die Casting of Semi-solid Magnesium Alloy

• Main Authors: Ruey-Jer Weng, 翁睿哲
• Other Authors: Weng-Sing Hwang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/72829990551811979270

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === Semi-solid metal casting is gaining more interest in the casting industry. Compared with the conventional pressure die casting process, semi-solid casting has some distinct advantages such as a more homogeneous microstructure, less porosity and improved mechanical properties. However, the complex rheology involved in the casting of semisolid metal alloys can result in very different flow behavior. Those simulation tools developed for traditional casting process can’t be applied to this process. In order to speed up the product development progress, a simulation system for semi-solid process is then desired. In addition to mold filling simulation, solidification analysis is also very important. Nevertheless, an accurate solidification model needs to know accurate thermal—physic properties. Therefore, there are two works in this study, one is to develop a mold filling simulation system for semi-solid processes, and the other is to measure interfacial heat transfer coefficient for AZ91D semi-solid magnesium alloy and SKD61 mold during solidification. For semi-solid process mold filling simulation, a program based on SOLA and Level Set Method has been developed to predict the filling of semi-solid AZ91D magnesium alloy for die-casting process. Power law model was used to describe the constitutive behavior of semi-solid metal slurry. Different constants of power law model were tested in the simulation system, and a series of short-shots experiments was conducted to validate the simulation results. The experimental results and simulation results were comparable. These results also showed that n set -0.85 and m set 100(Pa ¢ s0.15) are suitable inputs in the power law equation for mold filling simulation of semi-solid AZ91D magnesium alloy with a piston speed of 0.5 m/s and feedstock temperature of 575 C. For the interfacial heat transfer coefficient measurement, the experiments were conducted with different solid fractions (22%, 45%, and 60%) of AZ91D. At the solid fraction of 60%, the experiments were also conducted under three different pressures II (4.9MPa, 9.8MPa, and 14.7MPa) in order to investigate the effects of pressure on heat transfer coefficient. The heat transfer coefficient values at various solid fractions and different pressures were obtained and compared. The results obtained from this study indicate that the profiles of heat transfer coefficients for semisolid AZ91D magnesium alloy with different solid fraction have similar tendency. And the heat transfer coefficient profile are different for liquid and smisolid AZ91D. The heat transfer coefficient profile of liquid AZ91D can be divided into four stages, while the heat transfer coefficient profiles of semisolid AZ91D lack the third stage. Furthermore, heat transfer coefficient would increase with increasing solid fraction during solidification process and increase with increasing operating pressure.