Effects of Solid Fraction on the Heat Transfer Coefficient at the Casting/Mold Interface for Permanent Mold Casting of AZ91D Magnesium Alloy

摘要

The interfacial heat transfer coefficient (HTC) between the steel mold and AZ91D magnesium (Mg) alloy that cast under various initial solid fractions were investigated in this study. The interfacial HTC was determined by using an Inverse Method with measured temperature data and known thermo-physical properties. A Computer Aided Cooling Curve Analysis technique was used to determine the solid fraction versus temperature relationship. To comply with the requirements of the Inverse Method, a one-dimensional heat transfer system from the casting to the mold was designed for the permanent mold casting of AZ91D Mg alloy in molten and semisolid states. Experiments were conducted with different initial solid fractions of 0, 30, and 50 percent. The results indicate that the HTC profile of molten AZ91D during solidification can be divided into five stages, while casting with semisolid AZ91D only into three. During each stage, the casting/ mold interfacial conditions vary, which in turn causes the HTC values to vary. These data are critical for any solidification model of permanent.