Grain refining mechanism in Mg-9Gd-4Y alloys by zirconium

The effect of different zirconium contents on the grain size of Mg-9Gd-4Y alloys and the grain refinement mechanism of zirconium have been studied. The results reveal that zirconium can refine the grains of the alloys to a large extent, and the grains become finer with an increase of zirconium content. Microstructural analysis shows that there is at least one zirconium rich core in almost each grain in alloys with a high zirconium content, whereas the characteristic zirconium rich cores are not found in the alloy with a low zirconium content. It is suggested that the grain refinement mechanism of zirconium in the low zirconium alloy is different from that in the high zirconium alloys: the zirconium works mainly by restricting grain growth in the low zirconium alloy, and by generating nucleants in the high zirconium alloys.