Determination of interfacial heat transfer coefficients for squeeze casting of magnesium alloy AZ91 with various section thicknesses

In the present work, a step die was made by P20 steel for squeeze casting magnesium alloy AZ91 with five different section thicknesses of 2, 4, 8, 12, and 20 mm under an applied pressure of 60MPa. K-type thermocouples were utilised to measure temperatures of the squeeze casting surfaces as well as three different depths, i.e., 2, 4, and 8 mm from the mould inner wall at each step. With the temperature measurements, interfacial heat transfer coefficients (IHTC) at the casting and mould inner surface and heat fluxes were determined by solving one-dimensional heat conduction formulae using the inverse method. The results of the calculated IHTCs showed that, upon the commencement of squeeze casting, the IHTC values for all the five steps rose very rapidly. Before decreasing, the IHTC at each step reached its own individual peaks. As the section step thickness changed from 2 mm (step 1) to 20 mm (step 5), the IHTC peak values increased significantly. It took comparatively longer time for a thicker step to reach its peak IHTC value, and also to descend its IHTC to a low and steady level.