Crystallography of recently developed grain refiners for Mg-Al alloys

The grain refinement potency of some recently reported grain refiners for Mg - Al based casting alloys, including TiC, TiN, SiC and TiB2, was investigated from a crystallographic viewpoint using the edge-to-edge matching model. The results show that TiB2 is more likely to form an energetically favourable orientation relationship with the Mg matrix, and it is predicted that TiB2 should have the best grain refinement efficiency. The other three compounds may also serve as heterogeneous nucleation sites, but are not likely to be as effective as TiB2. The present analysis provides a better rationale of the superior grain refinement performance of TiB2 compared with SiC.