2021年, 第18卷, 第1期　
刊出日期：2021-01-28

  

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Research & Development
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  Microstructure and mechanical properties of AZ91D magnesium alloy by expendable pattern shell casting with different mechanical vibration amplitudes and pouring temperatures

  Suo Fan, He-bao Wu, Jin-xiu Fang

  《中国铸造》英文版. 2021, 18(1): 1-8. https://doi.org/10.1007/s41230-021-0113-z

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  To refine the microstructure and improve the mechanical properties of AZ91D alloy by expendable pattern shell casting (EPSC), the mechanical vibration method was applied in the solidification process of the alloy. The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91D magnesium alloy were studied. The results indicated that the mechanical vibration remarkably improved the sizes, morphologies and distributions of the primary α-Mg phase and β-Mg₁₇Al₁₂ phase, and the densification and tensile properties of the AZ91D alloy. With an increase in amplitude, the microstructures were gradually refined, resulting in a continuous increase in mechanical properties of the AZ91D alloy. While, with the increase of pouring temperature, the microstructures were continuously coarsened, leading to an obvious decrease of the mechanical properties. The tensile strength and yield strength of the AZ91D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃ were 60% and 38% higher than those of the alloy without vibration, respectively.
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  Microstructures and tensile properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements of Y, Bi, Sb and Sr

  He-shuai Yu, Xue-feng Guo, Hong-bao Cui

  《中国铸造》英文版. 2021, 18(1): 9-17. https://doi.org/10.1007/s41230-021-0117-8

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  The microstructures and mechanical properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements Y, Bi, Sb and Sr were investigated and compared. Results show that the microstructure of the as-cast Mg-5Sn-1Si alloy consists of α-Mg, Mg₂Si, Mg₂Sn and Mg₂(Si_xSn_1-x) phases. After adding 0.8wt.% Y, 0.3wt.% Bi, 0.9wt.% Sb and 0.9wt.% Sr, respectively into the Mg-5Sn-1Si magnesium alloy, Mg₂₄Y₅, Mg₃Bi₂, Mg₃Sb₂ and Mg₂Sr phases are precipitated accordingly. Trace elements can refine α-Mg grain and Chinese script-shaped Mg₂Si phase. Refinement efficiency of different trace elements on α-Mg grain and Mg₂Si phase is varied. Sr element has the best refinement effect, followed by Sb and Bi, while Y has the least refinement effect. Mg-5Sn-1Si-0.9Sr alloy has higher tensile properties than the other three modified alloys. The refinement mechanism of Y, Bi and Sr elements on Mg-5Sn-1Si magnesium alloy can be explained by the growth restriction factors and the solute undercooling. For Mg-5Sn-1Si-0.9Sb alloy, the heterogeneous nuclei of Mg₃Sb₂ phase is the main reason for the refinement of grains and second phases.
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  Cooling control for castings by adopting skeletal sand mold design

  Jin-wu Kang, Hao-long Shangguan, Fan Peng, Jing-ying Xu, Cheng-yang Deng, Yong-yi Hu, Ji-hao Yi, Tao Huang, Long-jiang Zhang, Wei-min Mao

  《中国铸造》英文版. 2021, 18(1): 18-28. https://doi.org/10.1007/s41230-021-0150-7

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  The cooling control of the melt during the casting process is of great significance. A comprehensive closed-loop cooling control of castings by adopting a skeletal sand mold design was proposed. The skeletal sand mold consisting of an adaptive shell, functional cavities and a support was designed and created based on the finite difference meshes of a casting. It was applied to a round wall test casting. Two kinds of skeletal sand molds, one with lattice support and the other with enforcing ribs for this casting were designed and printed out by the 3D printing (3DP) method. Aluminum alloy A356 was cast by using these two sand molds. The first mold was cooled by natural convection, the other one by water spray cooling. Two sound castings were obtained. The sand mold temperature, cooling curves, microstructures, mechanical properties, residual stress and deformation were measured, compared and discussed. Water spray cooling hastened the cooling rate by 62%, increased the content of Mg and Cu in the α-Al matrix, improved the mechanical properties, and altered the surface residual stress state.
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  Hot tearing behavior of NZ30K Mg alloy under progressive solidification

  Ke Wang, Peng-huai Fu, Li-ming Peng, Ying-xin Wang, Wen-jiang Ding

  《中国铸造》英文版. 2021, 18(1): 29-36. https://doi.org/10.1007/s41230-021-0066-2

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  Progressive solidification is usually considered an effective strategy to reduce the hot tearing susceptibility of a cast component. In this study, special constrained plate castings with progressive changes in cross-section were designed, which enabled progressive solidification. The hot tearing behavior of a newly developed NZ30K Mg alloy (Mg-3.0Nd-0.2Zn-Zr, wt.%) was studied under progressive solidification using various mold temperature distributions and constraint lengths. Of these, a homogeneous mold temperature distribution is found to be the best option to avoid hot tearing, followed by a local low mold temperature distribution (with a chiller), then a gradient mold temperature distribution. Unexpectedly, compared with the homogeneous mold temperature distribution, adding a chiller does not provide any further reduction in the hot tearing susceptibility of the NZ30K Mg alloy. A high mold temperature and a short constraint length increase the hot tearing resistance of cast Mg alloys. Progressive solidification is not a sufficient and necessary condition to avoid the formation of hot tearing. The two key factors that determine the occurrence of hot tearing under progressive solidification are the maximum cooling rate and the constraint length. Decreasing these values can reduce the incidence of hot tearing.
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  Grain refinement of primary silicon in hypereutectic Al-Si alloys by different P-containing compounds

  Benson Kihono Njuguna, Jia-yan Li, Yi Tan, Qian-qian Sun, Peng-ting Li

  《中国铸造》英文版. 2021, 18(1): 37-44. https://doi.org/10.1007/s41230-021-0074-2

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  The grain refinement behavior of Si-3P, Si-25Mn-10P, and Al-10Si-2Fe-3P master alloys on hypereutectic Al-24Si alloy was studied. Microstructure analysis indicates that the P-containing compounds in the three master alloys are SiP, MnP, and AlP, respectively. The coarse flower-like primary silicon in the Al-24Si alloy transforms into smaller, well-distributed blocks with the addition of various master alloys. When pouring at 840℃, the average grain size of the primary silicon refined by Si-25Mn-10P master alloy with a holding time of 30 min is about 18 μm, which is significantly smaller than those refined by Si-3P and Al-10Si-2Fe-3P master alloys. The grain size shows an increasing trend when the holding time is further prolonged. Higher holding temperature has a positive effect on the grain refinement of Si-25Mn-10P master alloy. The grain refinement mechanism of the three master alloys was also discussed.
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  Segregation in squeeze casting 6061 aluminum alloy wheel spokes and its formation mechanism

  Fan-bo Meng, Hong-jun Huang, Xiao-guang Yuan, Xue-jian Lin, Ze-wen Cui, Xian-lei Hu

  《中国铸造》英文版. 2021, 18(1): 45-51. https://doi.org/10.1007/s41230-021-0079-x

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  Segregation can seriously damage the mechanical properties of the aluminum alloys. 6061 aluminum alloy wheel spokes were prepared by squeeze casting. To investigate the formation mechanism of segregation, the microstructure of the alloy was observed using scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and electron microprobe analysis methods. The Gibbs energy of each phase during solidification was calculated by JMatPro. Results show that the segregation phases in the R-joint of the wheel spokes are mainly composed of Mg₂Si, β-AlFeSi and Al₅Cu₂Mg₈Si₆ intermetallics. During the solidification of the 6061 aluminum alloy wheels, Mg₂Si and α-AlFeSi phases precipitate in the mushy zone at first. With the decrease of temperature, α-AlFeSi transforms into β-AlFeSi, while Al₅Cu₂Mg₈Si₆ precipitates from the solid-state aluminum alloy after solidification. Segregation at the R-joint of wheel spokes is mainly caused by insufficient cooling, so the cooling during alloy solidification should be enhanced to avoid segregation.
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  Quantitative models for microstructure and thermal conductivity of vermicular graphite cast iron cylinder block based on cooling rate

  Qing-yi Liu, Xiao-fu Zhang, Yu-cheng Sun, Ai-long Jiang, Ji-chao Li, Hong-liang Zheng, Xue-lei Tian

  《中国铸造》英文版. 2021, 18(1): 52-59. https://doi.org/10.1007/s41230-021-0005-2

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  The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron (VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy (OM), scanning electrical microscopy (SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.
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  Influence of niobium and yttrium on plastic deformation energy and plasticity of Ti-based amorphous alloys

  Sheng-feng Shan, Hao Wang, Bing Zhang, Yuan-zhi Jia, Ming-zhen Ma

  《中国铸造》英文版. 2021, 18(1): 60-67. https://doi.org/10.1007/s41230-021-0139-2

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  Many amorphous alloys have been developed to date, but the low plasticity has limited their application. To achieve an amorphous alloy with high plasticity, a series of (Ti₄₀Zr₂₅Cu₉Ni₈Be₁₈)_100-xTM_x (x=0, 1, 2, 3, 4 at.%, TM=Nb, Y) alloys were designed to study the influence of Nb and Y addition on the plasticity. The amorphous samples were prepared using the vacuum melting and copper mold casting process. The microstructures, glass forming ability and mechanical properties of the alloys were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), depth-sensitive nanoindentation, and uniaxial compressive test. The plasticity of different bulk amorphous alloys was investigated by measuring the plastic deformation energy (PDE) during loading. The relationship between the PDE value and plasticity in bulk amorphous alloys was explored. Results show that Nb addition decreases the PDE value and promotes the generation of multiple shear bands, which significantly increases the fracture strength and plasticity, while the addition of Y element reduces the fracture strength and plastic strain of the alloy.
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  Corrosion and chemical behavior of Mg₉₇Zn₁Y₂-1wt.%SiC under different corrosion solutions

  Di-qing Wan, Yan-dan Xue, Jia-jun Hu, Hou-bin Wang, Wei Liu

  《中国铸造》英文版. 2021, 18(1): 68-74. https://doi.org/10.1007/s41230-021-0009-y

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  To explore the corrosion properties of magnesium alloys, the chemical behavior of a high strength Mg₉₇Zn₁Y₂-1wt.%SiC alloy in different corrosion environments was studied. Three solutions of 0.2 mol·L^-1 NaCl, Na₂SO₄ and NaNO₃ were selected as corrosion solutions. The microstructures, corrosion rate, corrosion potential, and mechanism were investigated qualitatively and quantitatively by optical microscopy (OM), scanning electron microscopy (SEM), immersion testing experiment, and electrochemical test. Microstructure observation shows that the Mg₉₇Zn₁Y₂-1wt.%SiC alloy is composed of α-Mg matrix, LPSO (Mg₁₂ZnY) phase and SiC phase. The hydrogen evolution and electrochemical test results reflect that the Mg₉₇Zn₁Y₂-1wt.%SiC in 0.2 mol·L^-1 NaCl solution has the fastest corrosion rate, followed by Na₂SO₄ and NaNO₃ solutions, and that the charge-transfer resistance presents the contrary trend and decreases in turn.
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  Shear bands of as-cast and semi-solid Ti₄₈Zr₂₇Cu₆Nb₅Be₁₄ bulk metallic glass matrix composites

  Xin-hua Huang, Lin-hao Zhu, Hong-min Guo, Hua-lan Jin, Xiang-jie Yang

  《中国铸造》英文版. 2021, 18(1): 75-82. https://doi.org/10.1007/s41230-021-0023-0

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  The as-cast Ti₄₈Zr₂₇Cu₆Nb₅Be₁₄ bulk metallic glass matrix composites (BMGMCs) were fabricated using a copper mold suction casting method. Then, the semi-solid BMGMC samples were obtained following an isothermal treatment (heating at 900℃ for 10 min, then cooling with water). The microstructure and compression property were investigated by scanning electronic microscopy (SEM) and universal mechanical tester. As a result of the isothermal treatment, the crystal shapes change from fine, granular, and dendritic to spherical or vermicular, and the average crystal size of the as-cast and semi-solid samples is 2.2 μm and 18.1 μm, respectively. The plasticity increases from 5.31% in the as-cast to 10.23% in the semi-solid samples, with an increase of 92.66%. The shear bands from different areas of the side surfaces of as-cast and semisolid compression fracture samples were observed. The characteristic changes of multiplicity, bend, branch and intersection of shear bands in different areas indicate that the deformation of as-cast and semi-solid samples is non-uniform during compression. It is found that poor plasticity of the as-cast samples or good plasticity of the semi-solid samples are reflected by characteristics of the shear bands. The semi-solid isothermal treatment improves the plasticity by forming large crystals which can block the expansion of shear bands and promote the multiplicity of shear bands.