Magnesium and magnesium alloy composite grain refiner and method for making same

The present invention provides one kind of grain refiner for magnesium and magnesium alloy and its preparation process. The grain refiner has the chemical composition including Al 15-37.5 wt%, C 5-12.5 wt%, Ce 5-20 wt% and Mg for the rest. Its preparation process includes the following steps: mixing aluminum powder, carbon powder and magnesium powder; pressing into block and stoving, setting inside corundum crucible and covering with refractory powder, isothermal treatment inside a box-type resistance furnace at 700-900 deg.c for 30-120 min to prepare Mg-Al4C3, and remelting together with magnesium ingot and intermediate Mg-25 %Ce alloy to prepare Mg-Al4C3-Ce as composite grain refiner finally. The present invention has convenient operation and easy use in industrial production, and the prepared composite grain refiner can fine grains of magnesium and magnesium alloy obviously.