When smelting magnesium alloy under the protected conditions, it is unavoidable completely for magnesium alloy melt to react with the atmosphere, that the loose reaction products are separated very difficultly from the alloy melt. Finally, they become the inclusions in the alloy, to deteriorate the mechanical properties and performance. In this paper, in order to evaluate the inclusions in the new-style Mg-Gd-Y-Zr alloy and find an effective method of eliminating inclusions, the morphology, size distribution, species of inclusions and their formation in the alloy smelting and casting conventionally under gas coverage are analyzed. The settling behavior of the inclusions is also analyzed by the calculations. There are complex inclusion mainly composed of Mg or Y oxide and flux inclusion with spherical, cluster, irregular and linear shape in the Mg-Gd-Y-Zr alloy. The average size and volume fraction of them are 12.7 µm and 0.26%, respectively. The frequency of the inclusions dramatically decreases with their size increasing. The volume of inclusions less than 20 µm occupies nearly 85% of the total volume of inclusions, while the percentage of inclusions less than\linebreak 45 µm is 96%. The calculations show that the settling velocity of inclusions is dependent on their size and density, and increasing the inclusion density can diminish the maximal size of the inclusions in the magnesium alloy, which the maximal size by the calculations is consistent with the experimental result.
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