THE ROLE OF BISMUTH IN GRAIN REFINEMENT OF MAGNESIUM AND ITS ALLOYS

摘要

The effect of Bismuth addition on the microstructure evolution of Mg and AZ31 Mg-alloy is studied at different cooling rates. A wedge-shaped copper mould was used to achieve continuous variation in cooling rates. Mg containing a small amount of bismuth produced a large decrease in the α-Mg grain size and suggested that that the presence of bismuth makes Mg less sensitive to the cooling rates employed. The macrostructure study of the static-mould direct-chill (DC) cast billets of AZ31 also supports the solute effect of bismuth on grain refinement of Mg and its alloys. The efficiency of Bi as a grain refiner solute can be seen with 50% average grain size reduction of AZ31 alloy at 0.2wt% Bi addition.