A new approach to designing a grain refiner for Mg casting alloys and its use in Mg–Y-based alloys

A totally new grain refiner, Al2Y, for cast Mg alloys has been predicted using the recently developed edge-to-edge matching (E2EM) crystallographic model. An addition of 0.6–1.0 wt.% Al into the Mg–10 wt.% Y melt promotes the in situ formation of Al2Y, which reduces the average grain size from about 180 to 36 μm. Active nucleation Al2Y particles were reproducibly observed at the centres of many refined grains. The excellent grain-refining efficiency is comparable to that of Zr for the same alloy, but the thermal stability of the grains refined by Al2Y is much higher than those refined by Zr up to a temperature of 550 °C for 48 h. The mechanisms of grain refinement and the superior thermal stability of the refined grains due to Al addition in the Mg–Y alloy are discussed based on the current experimental results.