Estimation of Interfacial Heat Transfer Coefficient in Indirect Squeeze Casting

摘要

In this work, indirect squeeze casting experiments were conducted using a 350-t Ube vertical squeeze caster to cast a hockey puck-like shaped casting of aluminum alloy A356. Experiments were conducted at two melt temperatures and at two pressure levels, while the die temperature was maintained close to 400 deg F. Pressure inside the die cavity was continuously monitored using a Kistler pressure probe and recorded using an associated data acquisition system. A CAD model of the hockey puck-like casting was imported to a commercial software package and solidification was simulated. Temperatures close to two mm from the casting-mold interface were measured using thermocouples mounted in the moving die half. While inputting heat transfer boundary conditions, it is assumed that there is no gap formation in squeeze casting and that the IHTC remains more or less constant during solidification in contract to gravity die casting where there is a marked decrease in the HTC value upon formation of an air gap between the casting and the mold during solidification. The IHTC was estimated by closely matching simulated and experimental cooling curves and was found to be close to 4500 W/m~2 K. Using this coefficient, the temperature distribution inside the casting was predicted. The modeling was validated by comparing predicted temperatures with measured temperatures in the mold. No significant enhancement in heat transfer at the metal-mold interface was observed for the high-pressure case when compared to the low-pressure case. This is due to the fact that metal pressures at the interface had already reached the threshold level beyond which no improvement in heat transfer occurs. Secondary Dendrite Arm Spacings (SDAS) were measured at various locations in the casting and compared with calculated cooling rates through the solidification range. The correlation of SDAS with cooling rate indicates a finer structure for a given cooling rate than previously reported in the literature, a result attributed to compositional modification of the alloy.