Effect of Sr content on microstructure and thermal conductivity of Al-Si alloy
Al-7Si-xSr,Al-12Si-xSr and Al-20Si-xSr alloys were prepared using pure aluminum,Al-20Si and Al-10Sr intermediate alloys as raw materials,and Sr as a modifier(content of 0.01%,0.02%,0.04%and 0.06%,mass fraction).The effect of Sr content on microstructure and thermal conductivity of the Al-Si alloy phase change heat storage materials was studied.The thermal conductivity of the alloys was measured by the Hot Disk thermal constant analyzer,and the microstructure of the alloys was observed and analyzed by scanning electron microscopy.The results show that adding the metamorphic element Sr to the Al-Si alloys will affect the thermal conductivity of the alloys.The thermal conductivity of the Al-7Si-0.04Sr alloy is increased by 73.47 Wem-1 K-1 compared with the Al-7Si alloy,the thermal conductivity of the Al-20Si-0.04Sr alloy is increased by 24.09 W·m-1·K-1 compared with the Al-20Si alloy,and the thermal conductivity of the Al-12Si-0.04Sr alloy is increased by 17.79 W·m-1 K-1 compared with the Al-12Si alloy.The increase of thermal conductivity of the Al-Si alloys is mainly related to the morphology of α(Al),eutectic silicon and primary silicon.After Sr modification,the three-dimensional morphology of eutectic Si in the Al-7Si alloy changes from lamellar to coral like,while the three-dimensional morphology of eutectic Si in the Al-12Si and Al-20Si alloys changes from lamellar to dendritic.Among them,the size of α(Al)in the Al-7Si alloy is significantly reduced,arranged tightly,and the spacing between secondary dendrite arms gradually decreases.The size of primary Si in the Al-20Si alloy significantly decreases,and its morphology changes from multi angular bulk to small pieces.The transformation of α(Al)morphology not only provides a fast channel for the transmission of free electrons,but also makes the arrangement of eutectic Si more regular,reducing the probability of free electron scattering,and has a significant effect on the thermal conductivity of the alloy.Eutectic Si changes from lamellar to coral or dendritic,which increases the average free path of electrons and is conducive to the transmission of electrons.The thermal conductivity of the Al-20Si alloy is closely related to the morphology of primary Si,the large-sized and fully shaped primary Si will undergo lattice vibration,which will improve the thermal conductivity of the alloy.