Modification mechanisms of hypereutectic Al-Fe alloys treated by Sm/Yb addition: Experiments and first-principles calculations

The effects of Sm/Yb on the microstructure, electrical conductivity (EC), thermal conductivity (TC) and thermal expansion properties of hypereutectic Al-Fe alloys were investigated by combining experiments and first-principles calculations. The microstructure evolution shows that the addition of Sm/Yb can effectively modify the primary Al13Fe4 phase, observing the best modification effect with 0.5 % Sm and 0.3 % Yb addition. Besides, adding Sm/Yb can simultaneously improve the EC, TC and thermal expansion performance of hypereutectic Al-Fe alloys. The improvement of thermal-physical properties is mainly due to the fact that the coarse primary Al13Fe4 intermetallic phase is modified to fine and star-like particles, which reduces the scattering of electrons and phonons. The first-principles calculation results show that both Sm/Yb can be stably adsorbed on the P1 terminal Al13Fe4 (010) surface, then inhibits the preferential growth of primary Al13Fe4 phase. The theoretical calculations and experimental results confirm that adsorption and constitutional undercooling are the main reasons for Sm/Yb modification. This study shows that rare earth elements modification is an effective method to control the morphology of primary phase and improve the thermal-physical properties of hypereutectic Al-Fe alloys.