The Influence of Rare Earth, Strontium and Calcium on the Thermal Diffusivity of Mg-Al Alloys

The microstructure and thermal diffusivity of as-cast AM60, AE63, AJ63 and AXJ620 alloys were investigated over the temperature range 20-300 degrees C. The microstructure of as-cast AM60 magnesium alloy consists of dendrites of alpha-Mg solid solution and divorced eutectic containing islands of alpha-Mg and Mg17Al12 phase. In regions adjacent with divorced eutectic, the supersaturation aluminum solute in the alpha-Mg matrix is observed. The addition of rare earth, calcium and strontium caused the decrease of the volume fraction of Mg17Al12 compound and aluminum content in a-Mg solid solution. Moreover, the intermetallic compounds such as: Al-11 RE3, Al4Sr, Al3Mg13Sr, Al2Ca are observed in the interdendritic regions. The thermal diffusivity of AM60 magnesium alloy increases with increasing temperature up to 150 degrees C, above this temperature the increase is less marked.The change in the slope of the temperature variation of the thermal diffusivity is caused by a precipitation of Mg17Al12 phase in the supersaturation of alpha-Mg areas neighboring the divorced eutectic alpha-Mg+Mg17Al12. The addition of rare earth, calcium and strontium caused the increase of the thermal diffusivity and thermal conductivity due to the decreasing of aluminum content in alpha-Mg matrix.