Comparative study on performance and microstructure of composite<br>water-soluble salt core material for manufacturing hollow zinc<br>alloy castings

FuchuLiuabSuoTubXiaolongGongbGuanjinLibWenmingJiangbXinwangLiubZitianFanb
aSchool of Mechanical Engineering and Electronic Information, China University of Geosciences, Wuhan, 430074, China
bState Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan, 430074, China

Highlights

  • A high-strength water-soluble composite KNO3-20 mol% KCl salt core material was successfully fabricated.
  • Bauxite and glass-fiber powder were added and acted as reinforcer.
  • The strengthening-toughening mechanisms of the salt core material was revealed.
  • A hollow-structure zinc alloy component was casting using the developed salt core material.

Abstract

The water-soluble salt core material has been successfully used for manufacturing hollow aluminum and magnesium alloy castings. However, there is rare report about the water-soluble salt core being used for lower melting point and higher density hollow zinc alloy castings. In order to obtain a high-performance composite water-soluble salt core material (CWSSC) which is suitable for manufacturing hollow-structure zinc alloy castings via high pressure die casting process, the comparative study on performance and microstructure of the salt cores fabricated by gravity casting technology was investigated using KNO3 and KCl as the base salt material with the reinforcements of bauxite or glass-fiber powder. The results show that CWSSC strengthened by reinforcements possesses many advantages of good surface quality and water-solubility rate, high bending strength and impact toughness, low shrinkage and moisture-absorption rate, and CWSSC composed of KNO3-20 mol% KCl with 15 wt% bauxite powder and 15 wt% glass-fiber powder has the better comprehensive performance, whose surface roughness is 0.4758 μm, bending strength is 46.6 MPa, impact toughness is 21.72 kJ/m2, and water-solubility rate is 178.21 kg/(min·m2) in still water at 80 °C with relatively low shrinkage and 24 h moisture-absorption rate. The scanning electron microscope analysis shows that the strengthening-toughening mechanisms of CWSSC mainly include refinement of the grain and deflection of the crack caused by KCl dendritic crystal and the rigid enhanced powders. A practical casting test has been conducted to prove that the developed CWSSC can be used to manufacture hollow-structure zinc alloy castings.

고압 다이캐스팅 공정을 통한 아연 합금 주조, 중력 주조 기술로 제작된 염심의 성능 및 미세 구조에 대한 비교 연구는 보크사이트 또는 유리 섬유 분말의 보강과 함께 기본 염 재료로 KNO3와 KCl을 사용하여 조사되었습니다.

그 결과, 보강재로 강화된 CWSSC는 우수한 표면 품질 및 수용성, 높은 굽힘 강도 및 충격 인성, 낮은 수축률 및 흡습율, 15wt%의 KNO3-20mol% KCl로 구성된 CWSSC의 많은 장점을 가지고 있음을 보여줍니다.

보크사이트 분말 및 15wt% 유리 섬유 분말은 표면 거칠기가 0.4758μm, 굽힘 강도가 46.6MPa, 충격 인성이 21.72kJ/m2, 수용성 비율이 178.21kg/(min·m2인 더 나은 종합 성능을 가지고 있습니다.

80°C의 정수에서 상대적으로 수축이 적고 24시간 수분 흡수율이 있습니다. 주사 전자 현미경 분석은 CWSSC의 강화 강화 메커니즘이 주로 KCl 수지상 결정 및 강성 강화 분말로 인한 균열의 편향 및 결정립의 미세화를 포함함을 보여줍니다.

개발된 CWSSC가 중공 구조의 아연 합금 주물을 제조하는 데 사용할 수 있음을 증명하기 위해 실제 주조 테스트가 수행되었습니다.

Fig. 8 Schematic diagram of strengthening-toughening mechanisms: (a)KNC + BP and (b)KNC + GP.
Fig. 8 Schematic diagram of strengthening-toughening mechanisms: (a)KNC + BP and (b)KNC + GP.
Fig. 3. The misrun defect of CWSSC when the reinforcement addition is over 30 wt%.
Fig. 3. The misrun defect of CWSSC when the reinforcement addition is over 30 wt%.
tes. Fig. 4. The surface macroscopic morphology of the different salt core materials: (a) KN, (b) KNC and (c) KN
tes. Fig. 4. The surface macroscopic morphology of the different salt core materials: (a) KN, (b) KNC and (c) KN
Fig. 5. Solidified microstructure of the different salt core materials: (a) KN, (b) KC, (c) KNC, (d) KNC þ BP, (e) KNC þ GP and (f) KNC þ BGP
Fig. 5. Solidified microstructure of the different salt core materials: (a) KN, (b) KC, (c) KNC, (d) KNC þ BP, (e) KNC þ GP and (f) KNC þ BGP
Fig. 6. The schematic diagrams of the solidified structure and crack propagation: (a) Unary salt and (b) Binary salt.
Fig. 6. The schematic diagrams of the solidified structure and crack propagation: (a) Unary salt and (b) Binary salt.
7. Fracture surface micro morphology of the different salt core materials: (a) KN, (b) KC, (c) KNC, (d) KNC þ BP, (e) KNC þ GP and (f) KNC þ BGP.
7. Fracture surface micro morphology of the different salt core materials: (a) KN, (b) KC, (c) KNC, (d) KNC þ BP, (e) KNC þ GP and (f) KNC þ BGP.
Fig. 8. Schematic diagram of strengthening-toughening mechanisms: (a)KNC þ BP and (b)KNC þ GP.
Fig. 8. Schematic diagram of strengthening-toughening mechanisms: (a)KNC þ BP and (b)KNC þ GP.
Fig. 9. Crack deflection microstructure of CWSSC strengthened by BP and GP: (a)KNC þ BP and (b)KNC þ GP
Fig. 9. Crack deflection microstructure of CWSSC strengthened by BP and GP: (a)KNC þ BP and (b)KNC þ GP
Fig. 10. Photograph of (a) the composite salt core and (b) hollow-structure zinc alloy castings by this composite salt core: b1-without and b2 with water soluble removing.
Fig. 10. Photograph of (a) the composite salt core and (b) hollow-structure zinc alloy castings by this composite salt core: b1-without and b2 with water soluble removing.

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