Grain refinement of as cast Mg-Mn alloy by simultaneous addition of trace Er and Al

A novel method for the grain refinement of as cast Mg-1.8Mn alloy by simultaneous addition of trace Er and Al was developed. A series of Mg-Mn alloys with systematic additions of Er alone (Er) or simultaneously with Al (Er/Al) were designed in order to illustrate the effects of Er/Al on the microstructure of the Mg-Mn alloy. The results showed that significant grain refinement was obtained by simultaneous addition of Er/Al. The grain size decreased remarkably from over 800 mu mm in the unrefined alloy to 150 mu m with the addition of 0.4 wt-% Er/Al. Adding Er alone to the Mg-Mn alloy did not evidently influence the grain size. The Al3Er phase was identified to be the dominant phase in the Er and Al containing alloys, besides elemental Mn particles. Based on the calculation of the planar disregistry between Al3Er and alpha-Mg, Al3Er particles could act as efficient heterogeneous nuclei of primary alpha-Mg during the solidification of Mg-Mn alloy.