Effect of cerium-rich mischmetal content on the growth morphology and microstructure evolution of undercooled Al-70 wt%Si alloys

The Al-70 wt%Si alloys with various cerium-rich rare earth contents undercooled by electromagnetic levitation were investigated, and the nucleation and growth, growth mode, and morphology evolution of primary Si were observed and recorded using a high-speed camera and scanning electron microscope. When the undercooling is lower than delta T-1, primary Si is coarse long plates with specific edges and faces, showing a characteristic of the lateral growth mode. When undercooling approaches delta T-2, the recalescence interface becomes dendritic and massive, and dendritic primary Si covers the surface of the alloys. The growth mode of primary Si shows a mixed growth mode of lateral and non-lateral. When undercooling exceeds delta T-2, the recalescence interface takes on a parallel shape and the morphology of primary Si transforms to homogeneous and fine spherical shapes with smooth surfaces, indicating a characteristic of the non-lateral growth mode. With an increasing RE content, critical undercooling, delta T-1 and delta T-2, gradually decreases, with the lowest values of 78 and 180 K for an RE content of 1.5%.

Automated summary

The effects of different cerium-rich rare earth contents on Al-70 wt%Si alloys were investigated using electromagnetic levitation. The nucleation and growth, growth mode, and morphology evolution of primary Si were observed. Results showed that with an increasing RE content, the critical undercooling gradually decreased.