Mechanism of grain refining by adding cerium in Mg and Mg alloys

The grain refinement study of magnesium and Mg-Al-Zn alloy which cannot be refined by zirconium was performed through adding cerium in pure magnesium and AZ31 alloy. The results show that the columnar and coarse grains can be obtained in pure Magnesium, but they are refined to small equiaxial grains with adding the minor content of cerium. The grain sizes of AZ31 alloy can be refined from 300 mu m to 30 mu m. Cerium is an efficient grain refiner for Mg and AZ31 alloy, since its solid solubility is negligibly small, causing rapid build-up of a solute enriched zone. Adding rare earth elements like cerium attributes the mechanism of grain size reduction by adding rare earth elements like cerium to supercooling of the solute rich zone ahead of the growth front.