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EFFECT OF GRAIN REFINING ON PRIMARYαPHASE IN SEMI-SOLID A356 ALLOY PREPARED BY LOW SUPERHEAT POURING AND SLIGHT ELECTROMAGNETIC STIRRING

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Acta Metallurgica Sinica(English Letters) 2008年第1期21卷 57-64页

作者： z. liu W.M. Mao z.D. z.ao Faculty of Material and Chemical Engineering Jiangxi University of Science and Technology Ganzhou 341000 China School of Material Science and Engineering University of Science ＆ Technology Beijing Beijing 100083 China

The semi-solid slurry of A356 alloy, which is grain-refined by Al-Ti-B master alloy, is prepared by low superheat pouring and slight electromagnetic stirring. The effects of grain refining on the morphology and the grain siz. of the primary α phase in the slurry manufactured are researched. The results indicate that the slurry with particle-like and rosette-like primary α phases can be prepared by low superheat pouring and slight electromagnetic stirring from liquid A356 alloy grain-refined, in which the pouring temperature can be suitably raised. Compared with the A356 samples without grain refining, the grain siz. and particle morphology of primary α phase as well as the distribution of the grain with particle-like or rosette-like along radial in the ingot in A356 are markedly improved by grain refining.

关键词： Semi-solid Grain-refined Low superheat pouring Slight electromagnetic stirring A356 alloy Al-Ti-B

MODELING OF STRAIN-INDUCED PRECIPITATION KINETICS IN Nb MICROALLOYED STEELS

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Acta Metallurgica Sinica(English Letters) 2006年第5期19卷 385-390页

作者： X. G. z.ou z. Y. liu D. Wu z. Li C.M. Li State Key Lab. of Rolling and Automation Northeastern University Shenyang 110004 China Baoshan Iron ＆ Steel Co. Ltd. Shanghai 201900 China Engineering ＆ Research Incorporation Limited WISDRI （Wuhan Iron ＆ Steel Design and

On the basis of the thermodynamic calculation of precipitation and considering the effect of strain on the precipitation behavior and chemical composition （Si and Mn）, the kinetics of precipitation from austenite has been investigated for different temperatures and strains. Nucleation theory and the solubility product of niobium, carbon, and nitrogen in austenite have been used to derive equations for the start time of precipitation as a function of temperature and composition. The value of n in Avrami equation was determined using the available experimental data from the published reports, which indicated that n is a constant independent of temperature and the end time of precipitation is a function of n and the start time of precipitation. The values of the start time and end time of precipitation predicted by the new model are compared with the experimental values and a good agreement was obtained between both.

关键词： strain-induced precipitation start time of precipitation end time ofprecipitation precipitation kinetics

Revealing the high-frequency attenuation mechanism of polyurea-matrix composites

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Acta Mechanica Sinica 2020年第1期36卷 130-142页

作者： J.Cheng z.L.liu C.C.Luo T.Li z.J.Li Y.Kang z.z.uang Applied Mechanics Laboratory School of Aerospace EngineeringTsinghua UniversityBeijing100084China Key Laboratory of Advanced Materials of Ministry of Education Department of Chemical EngineeringTsinghua UniversityBeijing100084China School of Materials Science and Engineering Tsinghua UniversityBeijing100084China

In this paper,a method for analyz.ng the high-frequency attenuation property of polyurea-matrix composites is developed by combining experimental,computational and theoretical ***,the ultrasonic experimental platform is established by solving the difficulties of high-frequency ultrasonic testing as high-frequency signal distortion,insufficient driving voltage and sampling rate failure,to study the dynamic mechanical properties(1-5 MHz.of pure polyurea and polyurea-matrix ***,the influences of composite parameters including the siz. and volume fraction of inclusions on wave attenuation performance under different frequencies are obtained and further verified by numerical ***,the contribution of inclusions to the wave attenuation performance is also theoretically *** is found that the increase of inclusion volume fraction and inclusion diameter will increase the attenuation coefficient of the *** the attenuation of composites with the inclusions of a 150-μm diameter and 30%as volume fraction can be 82%higher than pure *** amplifying attenuation effect of inclusions is mainly attributed to the scattering effect,which is verified by comparing numerical and theoretical results.

关键词： Polyurea Viscoelastic Dynamic mechanical properties Ultrasound

MICROSTRUCTURE TRANSFORMATION IN THE WELDING HEAT AFFECTED z.NE OF 800MPa GRADE ULTRA FINE STRUCTURED STEEL

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Acta Metallurgica Sinica(English Letters) 2004年第3期17卷 238-246页

作者： J.B. liu L.J. Hu Y.T.Wang z. Q. liu K. Miao z.L. Tian Huaz.ong University of Science and Technology Wuhan 430074 China Technology Center of Wuhan Iron and Steel (Group) Corporation Wuhan 430080 China Central Iron and Steel Research Institute Beijing 100080 China

The transformation behavior and microstructure development in the heat affected z.ne(HAz.of 800MPa grade ultra fine structured steel was *** was found that the HAz.has intermediate temperature transformation characteristics in a wide range of cooling rates,with the bainite sheaves consisting of bainite ferrite plates without carbide precipitation and retained austenite in the fast cooling *** relatively high cooling rates,which corresponded to low heat inputs,the hardness of the simulated HAz.was above that of the base *** the cooling rate was below 9C/s,the welding HAz.would have an obvious *** analysis of transformation rates in continuous cooling processes was completed by numerical differential *** result indicated that the microstructure transformation rate of the HAz.in 800MPa grade ultra fine structured steel changed sharply to slow speeds when the cooling time t8/5 is longer than 7s.

关键词： ultra fine structured steel weld heat affected z.ne transformation rate microstructure

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Az.1D EXTRUDED TUBE

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 203-208页

作者： B.Y. Yu C.L. Bao H.W. Song z. liu H.P. Yu School of Materials Science and Engineering Shenyang University of Technology Shenyang 110023 China

The effect of extrusion ratio on microstruetures and mechanical properties of magnesium alloy Az.1D extruded tube at 430℃ has been studied. After the evolution of microstracture and mechanical properties of Az.1D during extrusion were studied, the following parameters were obtained： tensile strength reached the climax value of 306.9MPa and elongation peak value of 10.1% at an extrusion ratio of 7.125, and with the increase of the extrusion ratio to 7.45, yield strength reached a top value of 285.795MPa with decreased tensile strength and elongation. It was concluded that mechanical properties of magnesium alloys Az.1D could be enhanced by adjusting the extrusion ratio near recrystalliz.tion.

关键词： magnesium tube microstructure tensile property

NUMERICAL SIMULATION OF MOLTEN POOL AND CONTROL STRATEGY OF KISS POINT IN A TWIN-ROLL STRIP CASTING PROCESS

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Acta Metallurgica Sinica(English Letters) 2008年第6期21卷 459-468页

作者： G.M. Cao C.G. Li z. Y. liu D. Wu G.D. Wang X.H. liu State Key Laboratory of Rolling ＆ Automation Northeastern University Shenyang 110004 China

Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

关键词： Twin-roll strip casting Coupled temperature and flow field Numerical simulation Kiss point Control strategy

Wide Absorption Spectrum Measuring Methods by DFB-LDs in Water Vapor Detection System

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Photonic Sensors 2014年第3期4卷 230-235页

作者： Y. N. liu J. CHANG J. LIAN Q. WANG G. P. LV W. J. WANG z. liu X. z. liu S. S. z.ANG z. L. WANG S. JIANG C. G. z.U W. WEI B.N. SUN School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology andApplication Shandong University Jinan 250100 China Institute of Automation Shandong Academy of Sciences Jinan 250014 China

Two measuring methods of the wide absorption spectrum by distributed feedback laser diodes （DFB-LDs） are presented in detecting the water vapor absorption line. One is the subsection scanning method, and it takes advantage of the wide spectrum tuning range by the temperature modulation and fast spectrum tuning speed by current modulation. Specifically, this method is realiz.d by dividing a target spectral region into several sections which correspond to the specific temperature of DFB-LD, scanning every section by current modulation for hundreds times, and averaging the data to raise the signal to noise ratio （SNR）, then combining all sections to get the whole spectrum. An accuracy of 10ppmv had been obtained in the measurement of water vapor with a 10-cm path length by this method. Another is data fitting method, based on the absorption line-shape function; the absorption line can be described by fitting with partial measured data. The fitting absorption line was fitted well with the measured data, and the square of correlation coefficient （R-square） was no less than 0.99.

关键词： DFB-LD wide spectrum subsection scanning data fitting water vapor detection

Structural Evolution of Fullerene during Mechanical Milling

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Journal of Materials Science & Technology 1999年第5期15卷 405-409页

作者： z. G.liu H. Ohi K. Tsuchiya and M. Umemoto(Department of Production Systems Engineering, Toyohashi University of Technology, Tempaku-cho,Toyohashi 441-8580, Japan To whom correspondence should be addressedE-mail: liuz.@umelab-61.tutpse.tut.ac.jp） K.Mas Toyohashi Univ Technol Dept Prod Syst Engn Toyohashi Aichi 4418580 Japan Toyama Natl Coll Technol Dept Mech Engn Toyama 939 Japan

Mechanical milling of fullerene (C60(C70)) was investigated to understand the structural evolu-tion. Mechanical milling could not destroy the molecular structure of C60(C70), while the longrange periodicity of the fCc crystalline structure was easiIy damaged. Longer miIIing time couldresult in the formation of C60(C70) polymer, including C60 dimer.

关键词： Figure Structural Evolution of Fullerene during Mechanical Milling Wang

Portfolio Construction for Value Appreciation

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Journal of Applied Mathematics and Physics 2016年第4期4卷 662-668页

作者： Michael Ha George z. liu Lihui z.eng Financial Mathematics Programme Xi’an Jiaotong-Liverpool University Suzhou China Risk Strategy & Derivatives Asia Pacific Allianz Global Investors Hong Kong China Risk Management Department Huatai-Pinebridge Fund Management Co. Ltd. Shanghai China

Background: While working as risk consultants at Barra in 1990’s, the first two authors decided to start collaborating on a research project with its first paper titled “Application of Volatility in Portfolio Construction” [1]. The third author was then a risk manager of a financial institution which was a client of Barra’s. Bringing his expertise in portfolio risk management, he joined the research team. Aim: The core of this paper lies in the construction of an investment portfolio with a main objective of value appreciation while examining its tracking error [1]-[3], a risk measurement with reference to a benchmark [1] [4]. The authors believe, while tracking error measurement is a common tool for portfolio risk management, total risk measurement is more important. The management goal is to minimiz. drawbacks using the technique of risk budgeting. These topics will be discussed in future research papers.

关键词： Tracking Error Beta Valuation Exposure Monitoring Rebalance