Effect of Thickness on the Thermal Conductivity and Microstructure of Die-Cast AZ91D Magnesium Alloy

Abstract

Magnesium alloys have many excellent properties and possess wide industrial application prospects. Sheets of AZ91D magnesium alloy with different thicknesses were produced by the die-cast process, and the cooling rates lay between 3.77 and 29.27 °C s⁻¹ with the thickness ranging from 1.5 to 6 mm. With the increasing thickness, the grain size increased, and the concentration of Al solute atoms in Mg matrix decreased. The second phases transformed from homogeneous fine particles and short strips at 1.5 mm to a network at 6 mm. These changes can be attributed to the cooling rate. The thermal conductivity was found to increase with the increasing thickness at the same temperature, and to increase with the increasing temperature at the same thickness. The minimum thermal conductivity (45.19 W (m K)⁻¹), and the maximum thermal conductivity (89.32 W (m K)⁻¹) were obtained at a thickness of 1.5 mm at 25 °C and a thickness of 6 mm at 150 °C, respectively. The grain size increased, and the Al solute atoms in Mg matrix decreased with the increasing thickness, which reduced the lattice irregularity and scattering of electrons and phonons, and resulted in an increase in the thermal conductivity.