Investigation on the microstructural refinement of an Mg–6 wt.% Zn alloy

The possibility to refine the microstructure of an Mg–6 wt.% Zn alloy utilising a physical grain refinement mechanism employing melt shearing under turbulence and casting near the liquidus temperature has been explored and compared against chemical grain refinement by Zr master alloy. The extremely coarse dendritic solidification microstructure of the base alloy can be somewhat refined through near liquidus-temperature casting. Employing melt shearing under turbulence in conjunction with liquidus-temperature casting promotes dramatic grain refinement and uniform polycrystalline microstructure throughout the cross section. The extent of microstructural refinement and uniformity achieved is better than chemical grain refinement using Zr containing master alloy in this investigation possibly due to inefficient Zr dissolution in the latter. The combination of chemical and physical grain refining promotes about a further 10% reduction in grain size over sheared and liquidus cast microstructures.