Effect of Cooling Rate and Modification by Strontium on the Thermal Conductivity of Al-8Si Alloy

Cooling rate plays a critical role in determining the thermal conductivity of Al-Si alloys. Although the effect of morphology and size of Si (changed by heat treatment) on its thermal conductivity has been investigated, the effect of cooling rates on thermal conductivity has not been well studied. In this study, we investigated the microstructure of an Al-8Si (with and without modification by Strontium (Sr)) alloy with cooling rates from 46.2 °C/s to 234 °C/s. It was found that the effect of cooling rate on thermal conductivity of Sr modification and Sr-free samples are opposite from each other. As a result, while the cooling rate increased from 46.2 °C/s to 234 °C/s, the calculated thermal conductivity increased from 145.3 MS/m to 151.5 MS/m for Sr-free Al-8Si alloy, and the calculated thermal conductivity was reduced from 187.5 MS/m to 176.7 MS/m for the Sr-modified Al-8Si alloy. By discussing how thermal conductivity correlates with eutectic silicon morphology and secondary dendrite arm spacing, the relationship between cooling rate and thermal conductivity were explained. This work suggests a new design strategy for improving the thermal conductivity of Al-Si hypoeutectic alloys.