  The three-dimensional structures of the primary Al3Sc particles in an Al-2Sc
master alloy were studied by synchrotron X-ray microtomography, scanning and
transmission electron microscopy. The Al3Sc phases were found to be a single
cube and a cluster of cubes. The surface area, equivalent diameter of the Al3Sc
cubes increased with the increasing of cube volume, but the specific surface
area decreases. The primary Al3Sc cubes and Al-matrix have the same crystal
orientation, indicating that the Al3Sc phases are the heterogeneous nucleation
sites for Al. The experimental results show that {\alpha}-Al2O3 are the
possible nucleation sites for the Al3Sc cubes.
