Investigation of the Interfacial Heat Transfer Coefficient at the Metal–Mold Interface During Casting of an A356 Aluminum Alloy and AZ81 Magnesium Alloy into Steel and Graphite Molds

Abstract

Many types of alloys can be cast in graphite molds. The advantage of using graphite molds is that graphite has a higher thermal conductivity than steel and provides a higher alloy cooling rate. In this work, the solidification conditions in graphite and steel molds are compared. Cylindrical ingots of A356 aluminum and AZ81 magnesium alloys were cast into steel and graphite molds, and the temperature was recorded by thermocouples positioned in both the ingots and the molds. Using the error function, which is a measure of the difference between the experimental and simulated temperatures, the interfacial heat transfer coefficient (IHTC) versus the ingot surface temperature curves were obtained. The peak IHTC for ingot casting in the graphite mold was 2–3 times higher than that for the steel mold for both alloys. The solidification time and cooling rate for the solidification of the A356 and AZ81 ingots with varied sizes in the graphite and steel molds were calculated based on the simulation results. The duration of the solidification process in the steel mold was nearly two times longer than that for ingots in the graphite mold. The cooling rate in the graphite mold was nearly 1.5–2 times higher than that in the steel molds.