Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of...Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However,when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction(EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.展开更多
The effect of different scales thermoelectric magnetic convection(TEMC)on the radial solidification microstructure of hypereutectic Al alloy has been investigated under transverse static magnetic field during directio...The effect of different scales thermoelectric magnetic convection(TEMC)on the radial solidification microstructure of hypereutectic Al alloy has been investigated under transverse static magnetic field during directional solidification,focusing on the formation of freckle.Our experimental and numerical simulation results indicate that the TEMC circulation at sample scale under transverse static magnetic field leads to the enrichment of solute Al on one side of the sample.The TEMC and the solute enrichment degree increase with the increase of magnetic field when the magnetic field increases to 0.5 T.The enrichment degree of solute elements under magnetic field is affected by temperature gradient and growth rate.The non-uniform distribution of solute Al in the radial direction of the sample results in the non-uniform distribution of primary dendrite arm spacing(PDAS).Moreover,the applied magnetic field can lead to freckle formation and its number increases with the increase of magnetic field.The change of freckle is consistent with the anisotropy TEMC caused by the anisotropy of primary dendrite or primary dendrite network under magnetic field.Finally,the mechanism of synergism effect of the anisotropy TEMC,the distribution of solute Al and the PDAS on freckle formation and evolution is studied during directional solidification under magnetic field.展开更多
Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult t...Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult to make significant breakthrough in conductivity performance.The hypoeutectic Al-5Ni alloy also possesses sound castability and is expected to be applied in thermal management applications.In this study,the effects of ytterbium(Yb element) at 0-0.5 wt% on the microstructures as well as the electrical/thermal conductivity and mechanical properties of the Al-5Ni alloy were systematically investigated.The experimental results indicate that the addition of Yb at a relatively low amount not only reduces the secondary dendrite arm spacing of the α-Al grains,but also modifies the morphology and distribution of eutectic boundary phase.Moreover,it is found that the dosage of Yb at 0.3 wt% in the Al-5Ni alloy can simultaneously improve the yield strength,ultimate tensile strength and electrical/thermal conductivity.The strengthening and toughening of the Al-5Ni alloy are mainly attributed to the decrease of secondary dendrite arm spacing and the improvement of eutectic phases.The transmission electron microscopy/selected area electron diffraction(TEM/SAED) analysis indicates that the ytterbium in Al-5Ni alloy will form Al_(3)Yb phase,which mainly agglomerates in the Al_(3)Ni phase region.This phase is helpful to decrease the solubility of impurity elements(e.g.,Fe and Si) in the α-Al matrix,which is beneficial to electrical/thermal conductivity.The value of this study lays foundation for manufacturing Al-Ni alloys with high thermal conductivity and acceptable mechanical properties.展开更多
This study proposes a framework to analyze the co-evolution between the remittance business for overseas Chinese and their institutions during 1860-1949. In particular, this paper focuses on the co-evolutions between ...This study proposes a framework to analyze the co-evolution between the remittance business for overseas Chinese and their institutions during 1860-1949. In particular, this paper focuses on the co-evolutions between their organizational fields and institutions. It shows that participants communicate, compete and cooperate through their organizational fields, and finally promote the remittance business. Since the three pillars of institutions---regulative, normative, and cultural-cognitive--correlate and interact with each other, it is found that institutions can promote the business of overseas remittance if the combination of these three pillars of institutions works well; otherwise, it ends the business with confusion.展开更多
基金supported by the European Space Agency through the Bl-inter 09 473220the National Natural Science Foundation of China(Nos.51571056 and 51690164)+1 种基金the "Shuguang Program" from Shanghai Municipal Education Commissionthe Shanghai Science and Technology Committee Grant(No.15520710900)
文摘Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However,when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction(EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.
基金the National Natural Science Foundation of China(Nos.51571056,51690164 and 51904183)the Technological Innovation Projects of Universities in Guangdong Province(Nos.2017KTSCX177 and 2020KQNCX084)+2 种基金China Postdoctoral Science Foundation(No.2020M683463)Guangdong Basic and Applied Basic Research Foundation(No.2019A1515110135)the Natural Science Foundation of Guangdong Province(No.2018A030310024)。
文摘The effect of different scales thermoelectric magnetic convection(TEMC)on the radial solidification microstructure of hypereutectic Al alloy has been investigated under transverse static magnetic field during directional solidification,focusing on the formation of freckle.Our experimental and numerical simulation results indicate that the TEMC circulation at sample scale under transverse static magnetic field leads to the enrichment of solute Al on one side of the sample.The TEMC and the solute enrichment degree increase with the increase of magnetic field when the magnetic field increases to 0.5 T.The enrichment degree of solute elements under magnetic field is affected by temperature gradient and growth rate.The non-uniform distribution of solute Al in the radial direction of the sample results in the non-uniform distribution of primary dendrite arm spacing(PDAS).Moreover,the applied magnetic field can lead to freckle formation and its number increases with the increase of magnetic field.The change of freckle is consistent with the anisotropy TEMC caused by the anisotropy of primary dendrite or primary dendrite network under magnetic field.Finally,the mechanism of synergism effect of the anisotropy TEMC,the distribution of solute Al and the PDAS on freckle formation and evolution is studied during directional solidification under magnetic field.
基金Project supported by the Guangdong Basic and Applied Basic Research Foundation (2019A1515110135,2021A1515010587)the Young Innovative Talents Projects of Universities in Guangdong Province(2020KQNCX084)the Guangdong Start-up Funds of DGUT (GC300502-52)。
文摘Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult to make significant breakthrough in conductivity performance.The hypoeutectic Al-5Ni alloy also possesses sound castability and is expected to be applied in thermal management applications.In this study,the effects of ytterbium(Yb element) at 0-0.5 wt% on the microstructures as well as the electrical/thermal conductivity and mechanical properties of the Al-5Ni alloy were systematically investigated.The experimental results indicate that the addition of Yb at a relatively low amount not only reduces the secondary dendrite arm spacing of the α-Al grains,but also modifies the morphology and distribution of eutectic boundary phase.Moreover,it is found that the dosage of Yb at 0.3 wt% in the Al-5Ni alloy can simultaneously improve the yield strength,ultimate tensile strength and electrical/thermal conductivity.The strengthening and toughening of the Al-5Ni alloy are mainly attributed to the decrease of secondary dendrite arm spacing and the improvement of eutectic phases.The transmission electron microscopy/selected area electron diffraction(TEM/SAED) analysis indicates that the ytterbium in Al-5Ni alloy will form Al_(3)Yb phase,which mainly agglomerates in the Al_(3)Ni phase region.This phase is helpful to decrease the solubility of impurity elements(e.g.,Fe and Si) in the α-Al matrix,which is beneficial to electrical/thermal conductivity.The value of this study lays foundation for manufacturing Al-Ni alloys with high thermal conductivity and acceptable mechanical properties.
文摘This study proposes a framework to analyze the co-evolution between the remittance business for overseas Chinese and their institutions during 1860-1949. In particular, this paper focuses on the co-evolutions between their organizational fields and institutions. It shows that participants communicate, compete and cooperate through their organizational fields, and finally promote the remittance business. Since the three pillars of institutions---regulative, normative, and cultural-cognitive--correlate and interact with each other, it is found that institutions can promote the business of overseas remittance if the combination of these three pillars of institutions works well; otherwise, it ends the business with confusion.
