Mechanical Properties of Salt Core Comprised of Alkali Carbonate and Alkali Chloride

The strength of salt core comprised of NaCI-NazC03, KCI-KzC03, KCI-NaCl and KZC03-NazC03 binary salt systems was investigated in order to develop expendable core for high pressure die casting using 4-point bending test, Vickers hardness measurement, and SEM observation of solidification structures and fracture surfaces. Bending specimens were fabricated from 10 K superheated molten salts by the permanent mold method. The results of the bending test showed that the KCI-KzC03 binary system offers quite high strength exceeding about 20 MPa. Moreover, especially high strength was obtained for the NaCI-NazC03 system whose strength value is higher than that of the KCI-KzC03 system. Also, the Vickers hardness of the NaCI-NazC03 system is higher than that of KCI-KzC03 system. In contrast to these binary systems, salt cores made of KCI-NaCl and KZC03-NazC03 binary salt systems could not be strengthened by mixing salt, due to phase separation of the solid solution phase crystallized from molten salt . In the solidification structures of NaCI-NazC03 system, dendritic or elliptic shaped primary phase and fine eutectic phase were found. As crack propagation is deflected by both the primary phase and fine eutectic phase, salt cores can be strengthened.