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Structures and macrosegregation of a 2024 aluminum alloy fabricated by direct chill casting with double cooling field

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China Foundry 2022年第1期19卷 1-8页

作者： Cheng zhu Zhi-hao Zhao qing-feng zhu Gao-song Wang Yu-bo Zuo Gao-wu Qin Research Center for Metallic Wires School of Materials Science and EngineeringNortheastern UniversityShenyang 110819China Key Laboratory of Electromagnetic Processing of Materials Ministry of EducationNortheastern UniversityShenyang 110819China Key Laboratory of Anisotropy and Texture of Materials Ministry of EducationNortheastern UniversityShenyang 110819China

Central region coarse grains and centerline segregation are common defects in aluminum ingots fabricated by direct chill(DC)casting.A double cooling field was introduced into the DC casting process to reduce these defects,whereby the external cooling was supplied by the mold and water jets,and intercooling was achieved by inserting a rod of the same alloy into the molten pool along the central axis of the ingot.Rather than forming a good metallurgical interface during solid-liquid compound casting,in the present work,the purpose of inserting the rod is to enforce internal cooling and consequently decrease the sump depth.Moreover,the insertion provides more nucleation sites with the unmoltenα-Al particles.The structure and the macrosegregation of 2024 Al alloy ingots prepared by DC casting with and without the inserts were investigated.Results show that when the inserting position is 50 mm above the upper edge of the graphite ring,significant grain refinement in the central region of the ingot and a reduced centerline segregation are achieved.

关键词： aluminum alloy direct chill casting double cooling field grain refinement macrosegregation

Line profile studies of hydrodynamical models of cometary compact H II regions

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Research in Astronomy and Astrophysics 2015年第6期15卷 828-848页

作者： feng-Yao zhu qing-feng zhu Department of Astronomy University of Science and Technology of China Key Laboratory for Research in Galaxies and Cosmology University of Science and Technology of China Chinese Academy of Sciences

We simulate the evolution of cometary H II regions based on several champagne flow models and bow shock models, and calculate the profiles of the [Ne II] fine-structure line at 12.81 μm, the H30α recombination line and the [Ne III] finestructure line at 15.55 μm for these models at different inclinations of 0°, 30° and 60°. We find that the profiles in the bow shock models are generally different from those in the champagne flow models, but the profiles in the bow shock models with lower stellar velocity （≤ 5 km s^-1） are similar to those in the champagne flow models. In champagne flow models, both the velocity of peak flux and the flux weighted central velocities of all three lines point outward from molecular clouds. In bow shock models, the directions of these velocities depend on the speed of stars. The central velocities of these lines are consistent with the stellar motion in the high stellar speed cases, but they are opposite directions from the stellar motion in the low speed cases. We notice that the line profiles from the slit along the symmetrical axis of the projected 2D image of these models are useful for distinguishing bow shock models from champagne flow models. It is also confirmed by the calculation that the flux weighted central velocity and the line luminosity of the [Ne III] line can be estimated from the [Ne II] line and the H30α line.

关键词： H II regions -- ISM kinematics and dynamics clusters -- line profiles

A Class of Backward Doubly Stochastic Differential Equations with Discontinuous Coefficients

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Acta Mathematicae Applicatae Sinica 2014年第4期30卷 965-976页

作者： qing-feng zhu Yu-feng SHI School of Mathematic and Quantitative Economics Shandong University of Finance and Economics Institute for Financial Studies and School of Mathematics Shandong University School of Statistics Shandong University of Finance and Economics

In this work the existence of solutions of one-dimensional backward doubly stochastic differential equations （BDSDEs） with coefficients left-Lipschitz in y （may be discontinuous） and Lipschitz in z is studied. Als... 详细信息

关键词： backward doubly stochastic differential equations backward stochastic integral comparisontheorem

Infinite Horizon Forward-Backward Doubly Stochastic Differential Equations and Related SPDEs

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Acta Mathematicae Applicatae Sinica 2021年第2期37卷 319-336页

作者： qing-feng zhu Liang-quan ZHANG Yu-feng SHI School of Mathematics and Quantitative Economics Shandong University of Finance and EconomicsandShandong Key Laboratory of Blockchain FinanceJinan 250014China Institute for Financial Studies and School of Mathematics Shandong UniversityJinanChina School of Science Beijing University of Posts and TelecommunicationsBeijing 100876China

A type of infinite horizon forward-backward doubly stochastic differential equations is studied.Under some monotonicity assumptions,the existence and uniqueness results for measurable solutions are established by means of homotopy method.A probabilistic interpretation for solutions to a class of stochastic partial differential equations combined with algebra equations is given.A significant feature of this result is that the forward component of the FBDSDEs is coupled with the backward variable.

关键词： infinite horizon forward-backward doubly stochastic differential equations homotopy stochastic partial differential equation

As-cast structure of DC casting 7075 aluminum alloy obtained under dual-frequency electromagnetic field

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International Journal of Minerals,Metallurgy and Materials 2014年第2期21卷 150-154页

作者： Zhi-hao Zhao Zhen Xu Gao-song Wang qing-feng zhu Jian-zhong Cui The Key Laboratory of the Ministry of Education of China for Electromagnetic Processing of Materials Northeastern University

We have experimentally determined the as-cast structures of semi-continuous casting 7075 aluminum alloy obtained in the pres-ence of dual-frequency electromagnetic field. Results suggest that the use of dual-frequency electromagnetic field during the semi-continuous casting process of 7075 aluminum alloy ingots reduces the thickness of the surface segregation layer, increases the height of the melt menis-cus, enhances the surface quality of the ingot, and changes the surface morphology of the melt pool. Moreover, low-frequency electromag-netic field was found to show the most obvious influence on improving the as-cast structure because of its high permeability in conductors.

关键词： electromagnetic fields： semi-continuous casting aluminum alloys as-cast structure

Investigation on Reaction Interface between the Aluminum and K2ZrF6 by Freezing the Molten Salt Reaction

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Acta Metallurgica Sinica(English Letters) 2017年第5期30卷 433-437页

作者： qing-feng zhu Fei Li Lei Li Wen-Jing Wang Gao-Song Wang Jian-Zhong Cui Key Laboratory of Electromagnetic Processing of Materials Ministry of EducationNortheastern UniversityShenyang 110819China School of Materials Science and Engineering Northeastern UniversityShenyang 110819China

A reaction interface between the aluminum and K_2ZrF_6 during molten salt reaction process was frozen by quenching the mold in water, and the interface structure was analyzed to determine the formation process of Al_3Zr. Results show that a clear conical interface existed between the K_2ZrF_6 and aluminum. A zirconium accumulation layer with the thickness of about 2–3 lm was formed at the aluminum side of the interface. Many initially formed Al_3Zr particles（with the size of 0.4–16 lm） distributed in this layer, most of which located at the interface. The morphology of Al_3Zr particles is closely related with their size. For the size of 0.4–1 lm, the Al_3Zr appeared as globular and ellipsoid shapes. When it grew to the size of 1–2 and 2–16 lm, it exhibited the rule cube shape, and rule cuboids shape, respectively.

关键词： Molten salt reaction Interface Aluminum Al3Zr particle Solidification

Dynamic and Static Aging Precipitation of β-Mg_(17)Al_(12) in the AZ80 Magnesium Alloy During Multi-directional Forging and Subsequent Aging

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Acta Metallurgica Sinica(English Letters) 2017年第10期30卷 941-948页

作者： qing-feng zhu Gao-Song Wang En-Ge Zhang Fan-Zheng Liu Zhi-Qiang Zhang Jian-Zhong Cui Key Laboratory of Electromagnetic Processing of Materials Ministry of EducationNortheastern University School of Materials Science and Engineering Northeastern University

Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.

关键词： Dynamic strain aging Precipitation AZ80 magnesium alloy Multi-directional forging Dynamic recrystallization

Effect of cooling rate on morphology and type of vanadium-containing phases in Al-10V master alloy

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China Foundry 2019年第5期16卷 300-306页

作者： qing-feng zhu Yi Meng Yan-lei Kang Shu-ping Kong Yang-peng Ou Yu-bo Zuo Key Laboratory of Electromagnetic Processing of Materials Ministry of Education Northeastern University Shenyang 110819 China School of Materials Science and Engineering Northeastern University Shenyang 110819 China School of Mechanical and Materials Engineering North China University of Technology Beijing 100144 China

Effects of cooling rates on the morphology, sizes and species of primary vanadium-containing phases in Al-10V master alloys were investigated. The results show that the primary vanadium-containing phases with different morphologies and compositions present in Al-10V master alloys at different cooling rates with the pouring temperature of 1,170 °C. When the Al-10V master alloy is solidified in the refractory mold at a cooling rate of 2 °C·s-1, the vanadium-containing phases are mainly plate-like Al10V phases, with the average size of 100.0 μm in the center and 93.2 μm at the edge of the ingot. When the master alloy is solidified in the graphite mold at a cooling rate of 24.3 °C·s-1, the primary vanadium-containing phases are dendritic Al3V phases, with the average length of 297.0 μm for the first dendrite in the center and 275.0 μm at the edge of the ingot. The secondary dendrite arm spacing (SDAS) is 9.5 μm in the center and 9.3 μm at the edge of the ingot, respectively. When the solidification is carried out in the copper mould at a cooling rate of 45.7 °C·s-1, the primary vanadium-containing phases are also Al3V phases but with smaller size, compared with that prepared at the cooling rate of 24.3 °C·s-1. As a result, the average length is 190.0 μm for the first dendrite in the center and 150.0 μm at the edge of the ingot. The SDAS is 9.8 μm in the center and 4.4 μm at the edge of the ingot, respectively.

关键词： Al-V master alloy cooling rate vanadium-containing phase solidification

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

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Acta Metallurgica Sinica(English Letters) 2015年第6期28卷 725-732页

作者： Lei Li Bo Xu Wei-Ping Tong Hui Zhang Chun-Yan Ban Li-Zi He Zhi-Hao Zhao Yu-Bo Zuo qing-feng zhu Jian-Zhong Cui Key Laboratory of Electromagnetic Processing of Materials Ministry of Education Northeastern University School of Metallurgy and Energy Hebei United University

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid （Pb）/ liquid （Sn） diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field （〈0.3 T）. When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level （0.8-5 T）, the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.

关键词： Microstructural evolution Crystallization behavior Dendrite growth Diffusion behavior Magnetic field Solidification pattern