Grain coarsening behavior of Mg-Al alloys with mischmetal addition

Small addition of mischmetal (MM) into aluminum alloys can lead to grain refinement. However, it is still uncertain whether the same effect applies to Mg-Al alloys. This work indicated that small amount of mischmetal addition ranging from 0.1 % to 1.2 % (mass fraction) did not cause grain refinement in Mg-Al alloys. On the contrary, they tended to coarsen the grains. When added into Mg-Al alloys, MM reacted preferentially with Al to form Al11MM3 phase. As Al11MM3 phase mainly distributed within alpha-Mg grains than at grain boundaries, it had little effect in restricting grain growth. In addition, MM reacted with Al-8(Mn, Fe)(5) or epsilon-AlMn particles to form Al-MM-Mn compounds, thus it reduced the amount of heterogeneous nuclei in the melt and resulted in remarkable grain coarsening.