Bending Strength of Salt Core Comprised of KCI-NaCl-Na2CO3-K2CO3 Systems

This paper introduction was written based on the ['Bending Strength of Salt Core Comprised of KCI-NaCl-Na2CO3-K2CO3 Systems'] published by ['The Japan Foundry Engineering Society'].

1. Overview:

  • Title: Bending Strength of Salt Core Comprised of KCI-NaCl-Na2CO3-K2CO3 Systems
  • Author: Jun Yaokawa, Daisuke Miura, Katsunari Oikawa, Koichi Anzai, Youji Yamada, and Hiroshi Yoshii
  • Publication Year: 2007
  • Publishing Journal/Academic Society: J. JFS, Vol. 79, No. 4 (2007) pp. 184~191, The Japan Foundry Engineering Society
  • Keywords: salt core, expendable core, carbonate, chloride, die casting, strength, deflection, decomposition
Figure 1 presents the calculated liquidus surface and eutectic line of the Na+-K+-Cl--CO₃²⁻ system using Thermo-Calc. It shows a wide composition range with liquidus temperatures between 873~973K.
Figure 1 presents the calculated liquidus surface and eutectic line of the Na+-K+-Cl--CO₃²⁻ system using Thermo-Calc. It shows a wide composition range with liquidus temperatures between 873~973K.

2. Abstracts or Introduction

This paper addresses the bending strength of water-soluble salt cores, a promising candidate for expendable cores in high-pressure die casting, which are essential for manufacturing undercut shaped products. The study investigates the strength of salt cores composed of a NaCl-KCI-Na2CO3-K2CO3 multi-component system. The research approach combines thermodynamic considerations of the salt mixture with experimental validation using a four-point bending test. Phase diagrams and thermodynamic functions, derived from thermodynamic data, predict four composition areas with high strength potential. Experimental strength mapping via bending tests reveals three composition areas achieving high strength exceeding 20MPa, aligning with theoretical predictions. These high-strength salt mixtures are deemed suitable for high-pressure die casting. The liquidus temperature for certain high-strength compositions ranges from 873K to 973K, facilitating salt core fabrication from molten salt. Another area exhibited high strength above 15 MPa, albeit with limited compositional range. SEM-EDX analysis indicates variations in sodium content within the primary chloride phase across specimens, suggesting sodium content's influence on primary phase strength and overall specimen strength. In chloride phase decomposition regions, strength is found to be relatively low when the primary phase is chloride.

3. Research Background:

Background of the Research Topic:

Aluminum alloy die casting is widely used in automotive parts due to its lightweight, high strength, corrosion resistance, and formability. However, conventional die casting methods struggle with undercut shapes. Expendable cores are crucial to overcome this limitation, making their development a renewed focus in die casting research. For undercut products in die casting, expendable cores must possess sufficient strength to withstand high-speed injection and high casting pressure, along with easy removal from the product.

Status of Existing Research:

Previous research explored water-soluble salt cores made from binary salt mixtures of chlorides and carbonates, specifically NaCl-Na2CO3 and KCI-K₂CO₃ systems. These studies demonstrated that salt cores made from these binary systems exhibit high strength without reinforcing materials, showing potential for die casting applications. For salt core溶融成形 (melting and forming), a low liquidus temperature around 873~973K is desirable. Suitable mixed salts with such liquidus temperatures include NaCl-K₂CO₃ and KCI-Na₂CO₃ systems, as well as MgCl₂, CaCl₂, Na₂SO₄, and CaCO₃. While the KCI-NaCl-K₂CO₃-Na₂CO₃ quaternary system exhibits a broad composition range with liquidus temperatures between 873~973K in phase diagrams, systematic investigations into its strength are lacking.

Necessity of the Research:

Despite the promising liquidus temperature range of the KCI-NaCl-K₂CO₃-Na₂CO₃ quaternary system, a systematic study of its strength properties is absent. Therefore, this research aims to comprehensively investigate the strength of this quaternary salt system to evaluate its suitability for expendable cores in die casting.

4. Research Purpose and Research Questions:

Research Purpose:

The primary purpose of this research is to investigate in detail the strength of the KCI-NaCl-K₂CO₃-Na₂CO₃ quaternary salt system. This investigation aims to assess the potential of this salt system for use in expendable cores for die casting applications, particularly focusing on achieving both high strength and suitable liquidus temperatures for core fabrication.

Key Research:

  • To clarify the relationship between the composition of the KCI-NaCl-K₂CO₃-Na₂CO₃ quaternary salt system and its bending strength.
  • To identify composition ranges within the quaternary system that exhibit high bending strength, suitable for high-pressure die casting.
  • To evaluate the liquidus temperatures of high-strength compositions to ensure feasibility for salt core production via melt processing.
  • To analyze the microstructure and phase composition of salt cores to understand the factors influencing their bending strength.

Research Hypotheses:

  • Specific composition areas within the KCI-NaCl-K₂CO₃-Na₂CO₃ quaternary system will exhibit high bending strength due to the formation of desirable microstructures, such as co-existence of primary phase and eutectic structure, as observed in binary salt systems.
  • The strength of salt cores is influenced by the primary phase composition, particularly the sodium content in the chloride primary phase.
  • Compositions with liquidus temperatures in the range of 873~973K within the high-strength areas of the KCI-NaCl-K₂CO₃-Na₂CO₃ system can be identified, making them suitable for expendable core fabrication.

5. Research Methodology

Research Design:

The research employs a combined approach of thermodynamic calculations and experimental validation. Phase diagrams and liquidus temperatures for the Na+-K+-Cl--CO₃²⁻ system were calculated using Thermo-Calc to predict composition areas with desired properties. Experimentally, a four-point bending test was used to measure the bending strength of salt cores with varying compositions within the quaternary system.

Data Collection Method:

  • Material Preparation: Test pieces were prepared using 99.5% purity KCl, NaCl, K₂CO₃, and Na₂CO₃. Salt mixtures were prepared with varying cation ratio X<0xE2><0x82><0x93> and anion ratio Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93> , systematically changing in 10 mol% increments to cover the Na+-K+-Cl--CO₃²⁻ system.
  • Four-Point Bending Test: The bending strength of the salt cores was evaluated using a four-point bending test.
  • Microstructural Analysis: Fractured surfaces after bending tests were examined using SEM to observe the microstructure.
  • Compositional Analysis: Energy Dispersive X-ray Spectroscopy (EDX) was used for local compositional analysis of the solidified structures.

Analysis Method:

  • Thermodynamic Calculation: Thermo-Calc software was used to calculate phase diagrams, liquidus surfaces, and eutectic lines for the Na+-K+-Cl--CO₃²⁻ system based on thermodynamic data.
  • Strength Mapping: Experimental bending strength data was mapped against composition to identify high-strength areas.
  • Microstructure-Strength Correlation: SEM and EDX analysis were used to correlate the observed microstructure and phase compositions with the measured bending strength.

Research Subjects and Scope:

The research focuses on salt cores made from the KCI-NaCl-Na₂CO₃-K₂CO₃ quaternary system, represented as Na+-K+-Cl--CO₃²⁻ system using ionic ratios X<0xE2><0x82><0x93> (cation ratio of K+) and Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93> (anion ratio of CO₃²⁻). The compositional scope systematically covers the quaternary system by varying X<0xE2><0x82><0x93> and Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93> in 10 mol% increments.

6. Main Research Results:

Key Research Results:

  • High Strength Areas: Bending strength mapping identified three composition areas (Areas A, B, and C in Fig. 5) exhibiting high strength exceeding 20MPa, and a portion of Area D with strength over 15MPa. These areas largely correspond to the composition areas predicted by thermodynamic calculations to have high strength.
  • Liquidus Temperature: Area A demonstrated both high strength (over 20MPa) and low liquidus temperatures (873~973K). Areas B and C also showed strength over 20MPa, but with slightly higher liquidus temperatures above 973K.
  • Microstructure: SEM observation of high-strength Areas A and C (Fig. 8) revealed a microstructure consisting of primary phase and eutectic structure, as predicted by phase diagrams.
  • Sodium Content Influence: SEM-EDX analysis indicated that sodium content in the primary chloride phase varies among specimens and influences the strength of the primary phase and overall bending strength. Higher strength was observed when sodium was present in the primary chloride phase, but excessive sodium content in primary chloride phase in certain composition led to phase decomposition and reduced strength.
  • Phase Decomposition and Strength Reduction: In compositions prone to chloride phase decomposition (Fig. 3), lower bending strength was observed, especially when the primary phase was chloride.

Analysis of presented data:

  • Figure 1 presents the calculated liquidus surface and eutectic line of the Na+-K+-Cl--CO₃²⁻ system using Thermo-Calc. It shows a wide composition range with liquidus temperatures between 873~973K.
  • Figure 2 shows vertical section phase diagrams at Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=0 mol% and 20 mol%, illustrating the chloride phase decomposition area at lower temperatures.
  • Figure 3 depicts the decomposition area of chloride phase calculated with Thermo-Calc, showing the compositional range of NaCl and KCl solid solution decomposition.
  • Figure 4 shows tie lines and liquidus lines at 923K, indicating the primary phase compositions and phase equilibria.
  • Figure 5 maps the four composition areas (A, B, C, D) predicted to have high strength based on deflection mechanism and factors reducing strength.
  • Figure 6 shows photographs of defects in cast specimens, including internal shrinkage (a) and surface irregularities and cracks (b).
  • Figure 7 is the bending strength map of the Na+-K+-Cl--CO₃²⁻ salt mixture, showing average bending strength values and liquidus/eutectic lines.
  • Figure 8 presents solidification structures of high-strength specimens from region A and C, showing primary and eutectic phases.
  • Figure 9 includes SEM micrographs and EDX analysis of fractured surfaces, revealing primary chloride and eutectic structures and compositional variations.
  • Figure 10 shows calculated K+ composition in cation for primary and eutectic chloride as a function of temperature, for different initial salt mixture compositions.
  • Figure 11 shows Vickers hardness measurements for Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=20mol% compositions, correlating hardness with composition and phase decomposition.

Figure Name List:

Figure 2 shows vertical section phase diagrams at Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=0 mol% and 20 mol%, illustrating the chloride phase decomposition area at lower temperatures.
Figure 2 shows vertical section phase diagrams at Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=0 mol% and 20 mol%, illustrating the chloride phase decomposition area at lower temperatures.
Figure 5 maps the four composition areas (A, B, C, D) predicted to have high strength based on deflection mechanism and factors reducing strength.
Figure 5 maps the four composition areas (A, B, C, D) predicted to have high strength based on deflection mechanism and factors reducing strength.
Fig. 7 Bending strength map of Na+-K+-Cl--CO₃²⁻ salt mixture with liquidus lines and eutectic line calculated with Thermo-Calc¹⁵).
Fig. 7 Bending strength map of Na+-K+-Cl--CO₃²⁻ salt mixture with liquidus lines and eutectic line calculated with Thermo-Calc¹⁵).
Fig. 9 SEM micrographs of broken surface (a)-(c), and results of EDX chemical analysis for selected area (d)-(f). (a) and (d): K⁺ composition in cation X<0xE2><0x82><0x93> =60 mol%, CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (b) and (e): X<0xE2><0x82><0x93> = 80 mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (c) and (f): X<0xE2><0x82><0x93>=90mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%.
Fig. 9 SEM micrographs of broken surface (a)-(c), and results of EDX chemical analysis for selected area (d)-(f). (a) and (d): K⁺ composition in cation X<0xE2><0x82><0x93> =60 mol%, CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (b) and (e): X<0xE2><0x82><0x93> = 80 mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (c) and (f): X<0xE2><0x82><0x93>=90mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%.
  • Fig. 1 Liquidus surface and eutectic line of Na+-K+-Cl--CO₃²⁻ system calculated with Thermo-Calc¹⁵).
  • Fig. 2 Phase diagrams of vertical section calculated with Thermo-Calc¹⁵). (a) CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=0 mol% (NaCl-KCl binary system). (b) Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%.
  • Fig. 3 Decomposition area of chloride calculated with Thermo-Calc¹⁵). Chloride phase solidified from molten salt, whose initial composition is the inside of this area, decomposes to KCl solid solution and NaCl solid solution.
  • Fig. 4 Tie lines and liquidus lines at 923K with the eutectic line calculated with Thermo-Calc¹⁵).
  • Fig. 5 Four composition areas of high strength expected by considering the deflection mechanism and some other factors which decrease strength.
  • Fig. 6 Photographs of some defects on the cross section of cast specimens. (a) K⁺ composition in cation X<0xE2><0x82><0x93> = 10 mol%, CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=60 mol%. (b) X<0xE2><0x82><0x93>=60 mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%.
  • Fig. 7 Bending strength map of Na+-K+-Cl--CO₃²⁻ salt mixture with liquidus lines and eutectic line calculated with Thermo-Calc¹⁵).
  • Fig. 8 Solidification structure of specimens with high strength. (a) K⁺ composition in cation X<0xE2><0x82><0x93> = 10 mol%, CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>=60mol% (region A). (b) X<0xE2><0x82><0x93>=0mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>-=20mol% (region C).
  • Fig. 9 SEM micrographs of broken surface (a)-(c), and results of EDX chemical analysis for selected area (d)-(f). (a) and (d): K⁺ composition in cation X<0xE2><0x82><0x93> =60 mol%, CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (b) and (e): X<0xE2><0x82><0x93> = 80 mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%. (c) and (f): X<0xE2><0x82><0x93>=90mol%, Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- = 20 mol%.
  • Fig. 10 K⁺ composition in cation for primary and eutectic chloride X<0xE2><0x82><0x93> (Chl.) calculated with Thermo-Calc¹⁵) plotted as a function of temperature. Initial cation compositions X<0xE2><0x82><0x93> of salt mixture are (a) 90 mol%, (b) 80 mol%, (c) 70 mol% and (d) 60 mol%, and initial CO₃²⁻ composition in anion Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- is 20 mol% for all.
  • Fig. 11 Vickers hardenss of Na⁺-K⁺-Cl⁻-CO₃²⁻ salt mixture at the initial CO₃²⁻ composition Y<0x43><0x6f><0x33><0x32><0xE2><0x82><0x93>- is 20 mol%.

7. Conclusion:

Summary of Key Findings:

This study identified four composition areas (A, B, C, and part of D) within the KCI-NaCl-Na₂CO₃-K₂CO₃ system that exhibit high bending strength suitable for expendable die casting cores. Areas A, B, and C achieved strengths exceeding 20MPa. Area A is particularly promising due to its combination of high strength and low liquidus temperature (873~973K). The high strength is attributed to the co-existence of primary and eutectic phases, supporting the deflection mechanism for strength enhancement. Sodium content in the primary chloride phase was found to be a critical factor influencing strength. Phase decomposition in chloride phases can lead to reduced strength.

Academic Significance of the Study:

This research provides a comprehensive understanding of the bending strength behavior of the KCI-NaCl-Na₂CO₃-K₂CO₃ quaternary salt system. It successfully integrates thermodynamic calculations with experimental validation to identify high-strength composition areas. The study highlights the importance of microstructure control, particularly the co-existence of primary and eutectic phases and the role of sodium content in the primary chloride phase, for achieving high strength in salt cores. The findings contribute to the fundamental understanding of salt material properties for die casting applications.

Practical Implications:

The identification of high-strength salt compositions with low liquidus temperatures, especially in Area A, has significant practical implications for die casting. Salt cores made from these compositions can withstand high-pressure die casting conditions and can be fabricated using melt processing due to their suitable liquidus temperatures. This opens up possibilities for manufacturing complex, undercut-shaped die-cast products using expendable salt cores based on the KCI-NaCl-Na₂CO₃-K₂CO₃ system.

Limitations of the Study and Areas for Future Research:

The study primarily focused on bending strength. Further research is needed to evaluate other critical properties such as thermal shock resistance, collapsibility, and removal characteristics of these high-strength salt cores. The influence of cooling rate and other solidification parameters on the microstructure and strength also warrants further investigation. Specifically for Area D, further investigation is needed to fully understand the narrow composition range exhibiting higher strength within the chloride phase decomposition region and optimize compositions to consistently achieve high strength while avoiding phase decomposition-induced weakness.

8. References:

  • 1) J. Yaokawa, D. Miura, K. Anzai, Y. Yamada and H. Yoshii J. JFS, to be published.
  • 2) J. Yaokawa, K. Anzai, Y. Yamada, H. Yoshii and H. Fukui: J. JFS, 76 (2004) 823
  • 3) J. Yaokawa, T. Sawada, K. Anzai, Y. Yamada, H. Yoshii and H. Fukui J. JFS, 78 (2006) 59
  • 4) C. Hayashi, T. Yamazaki, T. Ishikuro and A. Urakami: ALUTOPIA, 35 (2006) 6, 22
  • 5) N. Mantani and T. Touhata: SOKEIZAI, 36 (1995) 2, 14
  • 6) R. Izawa, T. Takayama, Y. Mizukusa and T. Komazaki: Report of Japan Die Casting Association, JD02 (2002) 223
  • 7) T. Manabe, M. Nitta and M. Yaguchi : SOKEIZ AI, 44 (2003) 12, 26
  • 8) Yamazaki, A. Takai, O. Murakami, M. Kawabata, O. Ito and M. Kawabata: SAE Technical Paper 2004-01-1447
  • 9) Y.Utsu, Japanese Patent Publication No.52-10803 (Mar. 26, 1977)
  • 10) R.W.Foreman, U.S. Patent No.4, 840, 219 (Jun. 20, 1989)
  • 11) General editors, L. P. Cook and H. F. McMurdie: Phase diagrams for ceramists vol.1, figure 1857 (Columbus, Ohio: American Ceramic Society) (1964)
  • 12) General editors, L. P. Cook and H. F. McMurdie : Phase diagrams for ceramists vol. 7, figure 6976, 7058, 7060, 7256 (Columbus, Ohio: American Ceramic Society) (1989)
  • 13) T. Sato: Technical Report of Tohoku Imp. Univ., XI (1934) 403
  • 14) J. Yaokawa, K. Oikawa and K. Anzai: CALPHAD to be printed
  • 15) B. Sundman, B. Jansson, J.-O. Andersson, CALPHAD 9 (1985) 153-190
  • 16) Y. Kagawa and H. Hatta: Ceramic Matrix Composites-Tailoring Ceramic Composites, (Agune Shohusha) (1990) 124
  • 17) S. Pehkonen J. Phys. D: Appl. Phys., 6 (1973) 544

9. Copyright:

  • This material is "Jun Yaokawa, Daisuke Miura, Katsunari Oikawa, Koichi Anzai, Youji Yamada, and Hiroshi Yoshii"'s paper: Based on "Bending Strength of Salt Core Comprised of KCI-NaCl-Na2CO3-K2CO3 Systems".
  • Paper Source: [https://doi.org/](DOI URL) (DOI URL was not provided in the text, please add if available)

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