抄録
It is known that when the degree of undercooling of a molten alloy increases, the solidified structure alters from equiaxed structure to columnar dendrites and finally to fine granular structure. In order to know the process of these structure changes with the increase of degree of undercooling, the solidification phenomenon and solidification structures of 99.99% Sn and Sn-Bi alloys undercooled at various degrees were observed. The maximum undercooling obtained in this experiment was about 27°C of Sn-4% Bi alloy.
With small degree of undercooling, the separation of necked-crystals which finally form an equiaxed zone from the container wall was clearly observed. As the degree of undercooling was increased, the separation of crystals stopped to form a stable solid skin on the container wall to produce the columnar dendrites. When the degree of undercooling was further increased, the fine grains were formed by the partial remelting of the necked dendrite arms.
