Semi-solid casting is performed at a temperature range that puts the metal between its liquidus and solidus temperatures. Physically, the metal is partially liquid and partially solid in this temperature window. Theoretically, the technique would result in minimal solidification shrinkage as well as lower reaction between the semi-solid liquid metal and the crucible. Moreover, the microstructure of the casting is expected to be homogeneous and fine-grained. One major challenge is overcoming the increased viscosity generated by the entanglement of dendritic structures in the semi-solid metal during casting.Two techniques were investigated as pathways to control the semi-solid metal and to realize the potentials of semi-solid casting. In the case of silver, dendritic arms in the liquid metal were changed to globular structure, resulting in a semi-solid metal that was fluid and entered the investment mold with less turbulence. In the case of titanium, the lower temperature of the metal helped reduce reactions with the crucible and investment. The cast pieces had good filigrees and microstructural homogeneity. Aside from these benefits, manufacturers could enjoy energy savings, longer crucible, gasket and machine life, as well as shorter cycle times for both casting and the burnout cycle.

Author: Dr. Boonrat Lohwongwatanai