Strength of Salt Core Composed of Alkali Carbonate and Alkali Chloride Mixtures Made by Casting Technique

The strength of four binary systems NaCl-Na2CO3, KCl-K2CO3, KCl-NaCl and K2CO3-Na2CO3 was investigated in order to develop expendable salt core for high pressure die casting processes. Four point bending test was conducted to determine the strength of specimens made from molten salts by using the permanent mold casting technique. The strength of the system NaCl-Na2CO3 was over 20 MPa. at the Na2CO3 composition between 20 mol% and 30 mol%, and between 50 mol% and 70 mol%. The highest strength was about 30 MPa at the composition of NaCl-70 mol%Na2CO3. This strength was 5 times as high as that of commonly used sand cores. The system KCl-K2CO3 also showed 20 MPa in strength. It was observed that there were the primary particles surrounded by the eutectic structure in the solidification structure of the systems NaCl-Na2CO3 and KCl-K2CO3 at the composition where the peak strength was obtained. The presence of the primary particles played an important role to strengthen the structure because the primary particles can prevent or deflect the crack propagation. In contrast to these binary systems, the systems KCl-NaCl and K2CO3-Na2CO3 were very brittle due to the phase decomposition or other solid-solid phase transformation of the solid solution phase. The strength of these systems was under 6 MPa.