Development of magnesium composite alloy by a new method combining B_2O_3 addition and melt stirring

For developing high performance magnesium alloys, a new method in combination of B2O3 addition and melt stirring was applied. When 0, 3%, 6% and 12%( mass fraction) B2O3 was added into pure Mg, many twins were produced in each alloy. The average grain size of Mg was about 200μm. In Mg-6Al alloy, the grain size is decreased from 50 to 35μm by B2O3 addition. In Mg-6RE (rare earth) alloys, the grain size is decreased from 35 to 15μm. The grain size of Mg-9Al- 6Ti-3B2O3 alloy is about 5μm. The hardness of pure Mg does not change by B2O3 addition. In Mg-6Al alloy, the hardness is increased by addition of 3% B2O3, however, the hardness of Mg-6RE alloy is decreased by B2O3 addition. Addition of B2O3 into Mg-Al, Mg-RE and Mg-Al-Ti alloys makes the fine grain structures, the hardness of Mg-RE alloy is decreased. This strange behavior may be interpreted with existence of many fine pores in the alloy. The mechanical properties of composite Mg-9Al-6Ti with 3%B2O3 are higher than those of AZ91C. The present results demonstrate the potential of this new method for developing high performance magnesium alloys.