Thermal diffusivity of the aluminum alloy Al-5Mg-2Si-Mn (Magsimal-59) in the solid and liquid states
E. Kaschnitz and M. Küblböck
The thermal diffusivity of the aluminum alloy Al-5Mg-2Si-Mn (Magsimal-59) was measured in the temperature range from room temperature to 670°C using the laser-flash technique. A commercial laser-flash system (Netzsch LFA 427) was used for the measurements. A short laser pulse of 300 μs was applied to heat the bottom surface of aedisk-shaped specimen, resulting in a time-dependent temperature increase at the top surface. A correction for the laser pulse-length as well as the surface radiation and convection was applied in order to evaluate the half time value of the temperature increase. The thermal diffusivity was calculated from the specimen thickness and the half time value. A sapphire crucible was used to contain the specimen in the mushy region and in the liquid state. As the laser is fired from below at the bottom surface of the specimen, the thickness of the melt has to be small to avoid significant buoyancy. The thermal diffusivity of the alloy in the liquid is drastically lower (approximately a half) than in the solid state of the alloy.