Effect of inoculation method of refiner on the grain refinement of AZ91 alloy

Grain refinement involving inoculation of a grain refiner was investigated for application to a commercial Mg alloy. Cylindrical pellets composed of a mixture of MnCO₃ and carbon powder with several different ratios were plunged into a commercial AZ91 alloy. The results show that the addition of the mixed pellets can more efficiently refine AZ91 compared to the individual use of carbon powder or MnCO₃. In particular, the addition of mixed pellets with a 3:7 ratio between MnCO₃ and carbon provides an excellent refining efficiency, decreasing grain size from 460µm to 52µm of the AZ91 alloy. This is attributed to inoculation of MnCO₃ and carbon, which brings about the formation of heterogeneous nucleants such as MgO, Al₄C₃, and Al₈Mn₅ before solidification of a-Mg and also to melt agitation by the release of CO₂ gas