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

摘要

The effect of Bismuth addition on the microstructure evolution ofMg and AZ31 Mg-alloy is studied at different cooling rates. Awedge-shaped copper mould was used to achieve continuousvariation in cooling rates. Mg containing a small amount ofbismuth produced a large decrease in the α-Mg grain size andsuggested that that the presence of bismuth makes Mg lesssensitive to the cooling rates employed. The macrostructure studyof the static-mould direct-chill (DC) cast billets of AZ31 alsosupports the solute effect of bismuth on grain refinement of Mgand its alloys. The efficiency of Bi as a grain refiner solute can beseen with 50% average grain size reduction of AZ31 alloy at0.2wt% Bi addition.