Abstract
The melt flow and the mold filling process in a precision casting tree for Ti-6Al-4V alloy castparts have been examined by casting trials, in which the molten alloy with an amount intentionally adjusted to be less than that required for complete filling is poured under a centrifugal force. By rotation of the tree on the horizontal plane the melt flows into mold cavities keeping contact with one of the vertical inside walls of a gate and a mold cavity. The melt in the cavity solidifies in a manner of directional solidification by accumulating solidifying layer from the far end of a cavity where the centrifugal force is maximum to a gate at which the force is minimum, namely according to the gradation of centrifugal force. The centrifugal force imposed on the melt enhances removal of gas bubbles which may evolve during the pouring of the melt into the mold cavity, reduces the number of gaseous defects to a negligibly small level at 30 G and improves the tensile strength of castparts. Dendrites are observed at the bottom of porosity where the inter-dendritic melt is sucked to the half thickness side by the solidification shrinkage. In mapping analysis of solute elements on cross sections of dendrite tips, micro segregation in a dendrite tip seems to be caused not during solidification but during transformation from the β to α phase on cooling of castparts.
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