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

Jun Yaokawa1, Daisuke Miura2, Koichi Anzai1, Youji Yamada3 and Hiroshi Yoshii3
1Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
2Graduate Student, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
3YAMAHA MOTOR CO. LTD., Iwata 438-0025, Japan

Abstract

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. [doi:10.2320/matertrans.48.1034]

Korea

고압 다이캐스팅 공정을 위한 소모성 솔트 코어를 개발하기 위해 4 가지 바이너리 시스템 NaCl–Na2CO3, KCl–K2CO3, KCl–NaCl 및 K2CO3–Na2CO3의 강도를 조사했습니다. 영구 주형 주조 기법을 사용하여 용융 염으로 만든 시편의 강도를 결정하기 위해 4 점 굽힘 시험을 수행했습니다.

NaCl-Na2CO3 시스템의 강도는 Na2CO3 조성에서 20 mol % ~ 30 mol %, 50 mol % ~ 70 mol % 사이에서 20 MPa 이상이었습니다. 가장 높은 강도는 NaCl–70 mol % Na2CO3 조성에서 약 30 MPa였습니다.

이 강도는 일반적으로 사용되는 모래 코어의 5 배에 달했습니다. 시스템 KCl–K2CO3도 20MPa의 강도를 나타 냈습니다. 피크 강도가 얻어지는 조성에서 NaCl–Na2CO3 및 KCl–K2CO3 시스템의 응고 구조에서 공융 구조로 둘러싸인 1 차 입자가 관찰되었습니다.

1 차 입자가 균열 전파를 방지하거나 편향시킬수 있기 때문에 1 차 입자의 존재는 구조를 강화하는 데 중요한 역할을 했습니다. 이러한 이원 시스템과 달리 KCl–NaCl 및 K2CO3–Na2CO3 시스템은 상 분해 또는 고용체상의 기타 고체-고체 상 변형으로 인해 매우 취약했습니다. 이 시스템의 강도는 6MPa 미만이었습니다. [doi : 10.2320 / matertrans.48.1034]

Fig. 1 Casting design of bending test specimens
Fig. 1 Casting design of bending test specimens
Fig. 2 Cross section of KCl-80 mol%K2CO3 specimen.
Fig. 2 Cross section of KCl-80 mol%K2CO3 specimen.
Fig. 3 Photographs of specimens at ambient temperature. (a) KCl–30 mol%NaCl. (b) K2CO3–50 mol% Na2CO3.
Fig. 3 Photographs of specimens at ambient temperature. (a) KCl–30 mol%NaCl. (b) K2CO3–50 mol% Na2CO3.
Fig. 7 The scanning electron microscope (SEM) images of solidified structure. (a) and (b) : NaCl–10 mol%Na2CO3. (c) and (d) : NaCl– 70 mol%Na2CO3.
Fig. 7 The scanning electron microscope (SEM) images of solidified structure. (a) and (b) : NaCl–10 mol%Na2CO3. (c) and (d) : NaCl– 70 mol%Na2CO3.
Fig. 9 The scanning electron microscope (SEM) images of broken surface. (a) : NaCl–10 mol%Na2CO3. (b) : NaCl–70 mol%Na2CO3.
Fig. 9 The scanning electron microscope (SEM) images of broken surface. (a) : NaCl–10 mol%Na2CO3. (b) : NaCl–70 mol%Na2CO3.
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