电磁悬浮过共晶Al-Si合金初生相偏聚行为研究

To reveal the physical mechanism of primary silicon (Si) segregation, the temperature and flow field of levitated droplets were studied using finite element simulation, aiming at the segregation phenomenon of primary Si phase in hypereutectic Al-18at%Si on the sample surface at electromagnetic levitation condition. The results show that the temperature gradient and reverse double eddy current flow field are the main factors that cause the primary Si phase to converge on the sample’s surface, which leads to the decrease in Si content in the levitated sample. Simultaneously, the morphology of the eutectic Si phase changed from needle to spherical and short rod with the increase of primary Si phase segregation. Additionally, tracer particles were introduced into the finite element calculation to simulate the movement of particles of different sizes in the Al-Si alloy melt. Combined with the experiment, it is found that the primary Si particles of different sizes migrate to the surface of the sample, and the smaller the particle size, the longer the migration time. Furthermore, the microhardness of the sample was studied. It was found that the primary Si phase was concentrated on the surface of the sample, which made the surface of the sample have ultrahigh hardness, about 13 times the internal hardness, thereby providing a new way to prepare composites.