The model has not only been used to understand the efficiency of currently existing grain refiners for both Al and Mg alloys [21], [31], [32] and [33], and it has also been successful in developing new grain refiners for cast Mg alloys, which includes ZnO [34] and Al2Y [35], [36] and [37]. From crystallographic point of view, ZnO is a powerful grain refiner for Mg alloy. But, the strong chemical reaction of the oxide with molten Mg limits its grain refining efficiency [34]. Al2Y particles in the melts act as very active heterogeneous nucleation sites and can significantly reduce the grain size of Mg castings from 200 μm to 30 μm [35], [36] and [37]