2022年, 第19卷, 第3期　
刊出日期：2022-05-28

  

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Research & Development
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  Effect of electromagnetic parameters on melt flow and heat transfer of AZ80 Mg alloy during differential phase electromagnetic DC casting based on numerical simulation

  Yong-hui Jia, Cheng-lu Hu, Qi-chi Le, Wen-yi Hu

  《中国铸造》英文版. 2022, 19(3): 191-200. https://doi.org/10.1007/s41230-022-1156-5

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  Based on multi-physical field coupling numerical simulation method, magnetic field distribution, melt flow, and heat transfer behavior of a Φ300 mm AZ80 alloy billet during differential phase electromagnetic DC casting (DP-EMC) with different electromagnetic parameters were studied. The results demonstrate that the increase in current intensity only changes the magnitude but does not change the Lorentz force's distribution characteristics. The maximum value of the Lorentz force increases linearly followed by an increase in current intensity. As the frequency increases, the Lorentz force's r component remains constant, and the z component decreases slightly. The change in current intensity correlates with the melt oscillation and convection intensity positively, as well as the liquid sump temperature uniformity. It does not mean that the higher the electric current, the better the metallurgical quality of the billet. A lower frequency is beneficial to generate a more significant melt flow and velocity fluctuation, which is helpful to create a more uniform temperature field. Appropriate DP-EMC parameters for a Φ300 mm AZ80 Mg alloy are 10-20 Hz frequency and 80-100 A current intensity.
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  Defect band formation in high pressure die casting AE44 magnesium alloy

  Ying-ying Hou, Meng-wu Wu, Feng Huang, Xiao-bo Li, Shou-mei Xiong

  《中国铸造》英文版. 2022, 19(3): 201-210. https://doi.org/10.1007/s41230-022-1220-1

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  The characteristics of defect bands in the microstructure of high pressure die casting (HPDC) AE44 magnesium alloy were investigated. Special attention was paid to the effects of process parameters during the HPDC process and casting structure on the distribution of defect bands. Results show that the defect bands are solute segregation bands with the enrichment of Al, Ce and La elements, which are basically in the form of Al₁₁RE₃ phase. There is no obvious aggregation of porosities in the defect bands. The width of the inner defect band is 4-8 times larger than that of the outer one. The variation trends of the distribution of the inner and outer defect bands are not consistent under different process parameters and at different locations of castings. This is due to the discrepancy between the formation mechanisms of double defect bands. The filling and solidification behavior of the melt near the chilling layer is very complicated, which finally leads to a fluctuation of the width and location of the outer defect band. By affecting the content and aggregation degree of externally solidified crystals (ESCs) in the cross section of die castings, the process parameters and casting structure have a great influence on the distribution of the inner defect band.
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  Microstructure evolution and age-hardening response in Mg-Sn-Sm alloys under a wide range of Sm/Sn ratio

  Feng Liu, Wen-xin Hu, Zheng-hua Yang, Wei Wang, Wei He

  《中国铸造》英文版. 2022, 19(3): 211-217. https://doi.org/10.1007/s41230-022-1120-4

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  The microstructure evolution and age-hardening response for different Sm/Sn ratios (0-2.55, in wt.%) of Mg-Sn-Sm alloys were investigated. The second phase formation in as-cast alloys and the Mg₃Sm precipitates formed in aged alloys were characterized using XRD, FESEM and HAADF-STEM with EDS techniques. Results indicate that the Sm/Sn ratio has a great influence on the phase constitution, α-Mg grain size and age-hardening response. With the increment of Sm/Sn ratio, Mg₄₁Sm₅ and thermally stable MgSnSm phases precipitate. When the Sm/Sn ratio is about 1.19, the secondary dendrite arm spacing of α-Mg grains significantly decreases. Furthermore, the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response, the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition (ageing at 220℃ for a short time of 4 h). This is attributed to the large volume fraction of needle-like Mg₃Sm precipitates formed in the α-Mg matrix during ageing treatment, which results in a significant precipitation strengthening effect.
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  Effect of surface Cr/C infiltration on microstructure, mechanical properties and wear resistance of high chromium cast iron

  Peng Chen, Zhao-yang Wu, Yan-liang Yi, Jian-bin Huang, Tao Shang, Wei Li

  《中国铸造》英文版. 2022, 19(3): 218-224. https://doi.org/10.1007/s41230-022-1110-6

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  A new type of high chromium cast iron (HCCI) was prepared, and its microstructure, mechanical properties, and abrasion resistance were investigated systematically. Results showed that after surface carburizing and chromizing, the microstructure of HCCI mainly consists of martensite, boride (M₂B), and carbide (M₇C₃), accompanied with a large amount of secondary precipitations M₂₃C₆. Moreover, the morphology and hardness of the carbide and boride in HCCI change little, while the volume fraction of carbide and boride increases from 16.23% to 23.16%. This effectively increases the surface hardness of HCCI from 64.53±0.50 HRC to 66.58±0.50 HRC, with the result that the surface of HCCI possesses a better abrasion resistance compared to the center position. Furthermore, the wear mechanism of HCCI changes from micro-plowing to micro-cutting with the increase of surface hardness.
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  Design and preparation of aluminum alloy with high thermal conductivity based on CALPHAD and first-principles calculation

  Ye Wang, Hui-jun Kang, Yu Guo, Hong-tao Chen, Mao-liang Hu, Ze-sheng Ji

  《中国铸造》英文版. 2022, 19(3): 225-237. https://doi.org/10.1007/s41230-022-1122-2

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  To obtain the aluminum alloy with high thermal and mechanical properties, the effects of alloying elements and the second phases on the thermal conductivity of Al alloys were investigated by CALPHAD and first-principles calculation, respectively. The properties of the second phases, including Young's modulus, Poisson's ratio and minimum thermal conductivity, were systematically studied. Results show that the ranking order of the effects of the alloying elements on the thermal conductivity is Mg>Cu>Fe>Si, and for Al-12Si alloys, the mathematical model of the relationship between the alloying elements and the thermal conductivity can be expressed as λ=ax²-bx+c when the second phase precipitates in the matrix. All kinds of ternary phases of Al-Fe-Si have higher deformation resistance, rigidity, theoretical hardness, Debye temperature and thermal conductivity than the other phases which possibly exist in the Al-12Si alloys. Based on the guidance of CALPHAD and first-principles calculation, the optimized chemical composition of Al alloy with high conductivity is Al-11.5Si-0.4Fe-0.2Mg (wt.%) with a thermal conductivity of 137.50 Wm^-1·K^-1 and a hardness of 81.3 HBW.
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  Effect of solution treatment on microstructure and mechanical properties of as-cast Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy

  Yu-dong Sui, Ye-hua Jiang, Qu-dong Wang

  《中国铸造》英文版. 2022, 19(3): 238-244. https://doi.org/10.1007/s41230-022-1076-4

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  Effect of solution treatment on microstructure and mechanical properties of Al-12Si-4Cu-2Ni-0.8Mg-0.2Gd alloy was investigated. Results show the Si particles become stable and more intermetallic compounds dissolve in the matrix after solution treatment at 500℃ for 2 h followed by 540℃ for 3 h (T4). The skeleton-like Al₃CuNi develops into two parts in the T4 alloy:one is Al₃CuNi which has the framework shape; the other is intermetallics including the Al₃CuNi (size:5-10 μm) and AlSiCuNiGd phases (size: ≤ 5 μm) with complex structure. Adding 0.2% Gd can improve the mechanical properties of the alloys after two-step solution treatment (500℃/2 h followed by 540℃/3 h), the hardness of the alloy increases from 130.9 HV to 135.8 HV compared with the alloy with one-step solution treatment (500℃/2 h), the engineering strength increases from 335.45 MPa to 352.03 MPa and the fracture engineering strain increases from 1.44% to 1.67%.
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  Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

  Gui-quan Wang, Zhong-li Liu, Yan-xiang Li, Xiang Chen

  《中国铸造》英文版. 2022, 19(3): 245-252. https://doi.org/10.1007/s41230-022-1204-1

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  The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron. Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed. It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix. More oxidized matrix is observed in gray cast iron due to its large specific surface area. The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer. By contrast, the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers. It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.
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  High-strength aluminum alloys hollow billet prepared by two-phase zone continuous casting

  Yao-hua Yang, Xue-feng Liu, Wang-zhang Chen

  《中国铸造》英文版. 2022, 19(3): 253-262. https://doi.org/10.1007/s41230-022-1036-z

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  The two-phase zone continuous casting (TZCC) technique was used to continuously cast high-strength aluminum alloy hollow billets, and a verified 3D model of TZCC was used to simulate the flow and temperature fields at casting speeds of 2-6 mm·min^-1. Hollow billets under the same conditions were prepared, and their macro/microstructures were analyzed by an optical microscope and a scanning electron microscope. During the TZCC process, a circular fluid flow appears in front of the mushy zone, and the induction heated stepped mold and convective heat transfer result in a curved solidification front with depressed region near the inner wall and a vertical temperature gradient. The deflection of the solidification front decreases and the average cooling rate in the mushy zone increases with increasing casting speed. Experimental results for a 2D12 alloy show that hot tearing periodically appears in the hollow billet accompanied by macrosegregation near the inner wall at casting speeds of 2 and 4 mm·min^-1, while macroscopic defects of hot tearing and macrosegregation weaken and the average size of columnar crystals in the hollow billets decreases with further increasing casting speed. 2D12 aluminum alloy hollow billets with no macroscopic defects, the finest columnar crystals, and excellent mechanical properties were prepared by TZCC at a casting speed of 6 mm·min^-1, which is beneficial for the further plastic forming process.
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  Quantitative multi-phase-field modeling of non-isothermal solidification in hexagonal multicomponent alloys

  Yong-biao Wang, Ming-guang Wei, Xin-tian Liu, Cong Chen, Jian-xiu Liu, Yu-juan Wu, Shuai Dong, Li-ming Peng

  《中国铸造》英文版. 2022, 19(3): 263-274. https://doi.org/10.1007/s41230-022-1123-y

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  A quantitative multi-phase-field model for non-isothermal and polycrystalline solidification was developed and applied to dilute multicomponent alloys with hexagonal close-packed structures. The effects of Lewis coefficient and undercooling on dendrite growth were investigated systematically. Results show that large Lewis coefficients facilitate the release of the latent heat, which can accelerate the dendrite growth while suppress the dendrite tip radius. The greater the initial undercooling, the stronger the driving force for dendrite growth, the faster the growth rate of dendrites, the higher the solid fraction, and the more serious the solute microsegregation. The simulated dendrite growth dynamics are consistent with predictions from the phenomenological theory but significantly deviate from the classical JMAK theory which neglects the soft collision effect and mutual blocking among dendrites. Finally, taking the Mg-6Gd-2Zn (wt.%) alloy as an example, the simulated dendrite morphology shows good agreement with experimental results.
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  Plasticity improvement of (Cu₄₃Zr₄₈Al₉)₉₈Y₂ bulk metallic glass composites by dispersed Ta particles

  Ke Yang, Bing Li, Xin Wang, Xin-hui Fan

  《中国铸造》英文版. 2022, 19(3): 275-280. https://doi.org/10.1007/s41230-022-9022-z

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  (Cu₄₃Zr₄₈Al₉)₉₈Y₂-based bulk metallic glass composites (BMGCs) with dispersed Ta particles (3vol.%, 6vol.%, 9vol.%) were successfully fabricated through suction casting. The thermal properties, microstructure, and mechanical properties of the BMGCs were systematically investigated. Ta particles are homogeneously dispersed in the amorphous matrix. Ta particle reinforced BMGCs exhibit similar thermal properties and glass-forming ability with the (Cu₄₃Zr₄₈Al₉)₉₈Y₂ base BMG. Compression test results show that the BMGC with 9vol.% Ta particles has superior mechanical performance with up to 15.7% compressive plastic strain, 2,216 MPa yield strength, and 2,260 MPa fracture strength at room temperature. These homogeneously distributed Ta particles act as discrete obstacles in the amorphous matrix, restricting the highly localized shear band. This results in the formation of multiple shear bands around the Ta-rich particles, which lowers the stress concentration, allowing the shear band to propagate further and improve plasticity.