1996 Volume 60 Issue 9 Pages 853-862
The melt flow and mold filling in precision casting of a Ti-6Al-4V alloy has been examined by casting trials, in which the molten alloy with an amount intentionally adjusted to be less than that for complete filling is poured into mold cavities under some centrifugal force. By rotation of the tree on the horizontal plane, the molten alloy flows into the mold cavities keeping contact with one of the vertical inside walls of a gate and a mold cavity. Solidification in the mold cavity proceeds mainly in a manner of directional solidification by accumulating the solidifying layer from the far end of a mold cavity where the centrifugal force is maximum to the gate at which the force is a minimum. The centrifugal force imposed on the melt enhances separation of gas bubbles which may evolve during pouring the melt into the mold cavity, reduces the number of gaseous defects to a level negligibly small at 30G, and improves mechanical properties of castparts. Detailed observation of the defects showed that dendrites appears at the bottom of porosity where the inter-dendritic melt is sucked to the half thickness side surface by solidification shrinkage. Micro segregation of solute in a dendrite tip seems to be caused not during solidification but during transformation from the β to α phase by mapping analysis.
