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THE INVESTIGATION ON THE RHEOLOGICAL BEHAVIOR OF SEMI-SOLID ALUMINUM ALLOY DURING DIE CASTING

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Acta Metallurgica Sinica(eng.ish Letters) 2002年第6期15卷 511-516页

作者： X.J. Yang and J.Liu School of mech.nic & electron.c eng.neering, Nanchang University, Jiangxi 330029, China School of mech.nic & electron.c eng.neering, Shanghai University, Shanghai 200072, China Sch. of mech. and electron. eng. Nanchang Univ. Nanchang 330029 China Sch. of mech. and electron. eng. Shanghai Univ. Shanghai 200072 China

Under the condition of die casting and reheating temperature of 570-580 degC, the rheological behavior of semi-solid aluminum alloy (A356) is pseudoplasticity at the shearrate of 2X10^-1X10^4s^(-1), and also shows dil... 详细信息

关键词： shear rate apparent viscosity viscosity model thixocasting

Water-Air Mixing Jet Produced by Electro-hydraulic Impulse Technology Streng.hening the Quality of Surface of Metal Materials

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Journal of Materials Science & Technology 2002年第3期18卷 194-196页

作者： Zhenfang LIAO and Shijin ZHANGcoll.ge of mech.nical eng.neering, Chongqing University, Chongqing 400044, China [ Manuscript received September 10, 2001, in revised form October 26, 2001] coll. of mech. eng. Chongqing Univ. Chongqing 400044 China

Electro-hydraulic impulse water-air mixing jet by which the quality of metal materials can be improved is described in this paper. The experimental results proved that the hardness and the micro-hardness of the surface layer of metal materials can be improved with this method, for example, the microhardness of CrWMn can be increased by 35.62 percent.

关键词： Electro-hydraulic impulse Water-air mixing jet Quality of surface

Study on Laser Transformation Hardening of HT250 by High Speed Axis Flow CO_2 Laser

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Journal of Materials Science & Technology 2003年第2期19卷 170-173页

作者： Yunxia YE, Yonghong FU and Yongkang ZHANGmech.nical eng.neering coll.ge, Jiangsu University, Zhenjiang 212013, China mech. eng. coll. Jiangsu Univ. Zhenjiang 212013 China

In this article, laser transformation hardening of HT250 material by high speed axis flow CO2 laser was investigated for first time in China. Appropriate laser hardening parameters, such as laser energy power P(W), laser scanning rate V(m/min), were optimized through a number of experiments. The effect of the mentioned parameters on the hardened zone, including its case depth, microhardness distributions etc., were analyzed. Through the factual experiments, it is proved that axial flow CO2laser, which commonly outputs low mode laser beam, can also treat materials as long as the treating parameters used are rational. During the experiments, the surface qualities of some specimens treated by some parameters were found to be enhanced, which does not coincide with the former results. Furthermore in the article, the abnormal phenomenon observed in the experiments is discussed. According to the experimental results, the relationship between laser power density q and scanning rate V is shown in a curve and the corresponding formulation, which have been proved to be valuable for choosing the parameters of laser transformation hardening by axial flow CO2 lasers, was also given.

关键词： Laser transformation hardening Hardened case Laser parameters Cast iron

Modification Effects of Lanthanum-Rich Mischmetal on A357 Alloy

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Journal of Rare Earths 2001年第1期19卷 49-52页

作者：李华基刘昌明李革胜薛寒松 coll. of mech. eng. Chongqing Univ. Chongqing 400044 China

A357 alloy was modified with lanthanum -rich mischmetal, and modification effects of the mischmetal on its as-cast and heat-treated structures, mech.nical properties and hydrogen content were investigated and compared with that of strontium metal. It is shown that the modification effect of La-rich mischmetal is better than that of strontium in the aspects of refining eutectic silicon, ejecting hydrogen from the melt and improving comprehensive mech.nical properties of the alloy. Therefore Al-Si-Mg alloy with high streng.h and improved toughness can be obtained by modification with La-rich mischmetal.

关键词： rare earths A357 alloy modification microstructure mech.nical properties

BREAKING WAVE FORCES ON VERTICAL CYLINDERS

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Journal of Hydrodynamics 2002年第4期14卷 110-112页

作者： Ma Ru-jian, Li Gui-xi Department of mech.nical and electron.c eng.neering, Jinan University, Jinan 250022, China Dept. of mech. and electron. eng. Jinan Univ. Ji'nan 250022 China

The breaking wave forces on vertical cylinders in shallow waters were studied by means of experimental methods. The results indicate that the breaking wave pressure is distributed exponentially with respect to water depth. An experimental formula was given using the test data. Compared with test data, the calculated breaking wave forces are in good agreement with the test data.

关键词： breaking wave forces pressure distribution of breaking waves experimental study

Heat transfer analysis for the roller shell under the condition of periodic thermal shock

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Journal of University of Science and Technology Beijing 2003年第6期10卷 44-47页

作者： Lihua Zhan and Xiaoqian Licoll.ge of Electro-mech.nical eng.neering, Central South University, Changsha 410083, China coll. of Electro-mech. eng. Central South Univ. Changsha 410083 China

According to the actual working conditions of roller shell in the process ofcontinuous roll casting, the Fourier heat transfer law is used to conduct the simulating analysisfor the temperature distribution of the roller shell under the condition of periodic thermal *** temperature variation law inside the roller shell is studied during the process of continuousroll casting, and the steady temperature distributions of the roller shell at different castingvelocities have been obtained when the thermal contact conductance between the roller shell and thecasting strip is considered.

关键词： roller shell thermal contact conductance (TCC) periodic thermal shock

Microstructure and Properties of Low Temperature Composite Chromized Layer on H13 Tool Steel

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Journal of Materials Science & Technology 2005年第2期21卷 251-255页

作者： Cuilan WU, Cheng.ing LUO and Ganfeng.ZOU coll.ge of mech.nical eng.neering, South China University of Technology, Guangzhou 510641, China coll. of mech. eng. South China Univ. of Technol. Guangzhou 510641 China

Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.

关键词： H13 tool steel Low temperature composite chromizing Nitride and carbide of chromium Microhardness Wear resistance

Microstructure and tensile behavior of hot extruded AZ91 alloys at room temperature

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Journal of University of Science and Technology Beijing 2002年第5期9卷 352-355页

作者： Yuanyuan Li, Datong Zhang, Ying Liu, Yan Long, and Weiping Chencoll.ge of mech.nical eng.neering, South China University of Technology Guangzhou 510640, China coll. of mech. eng. South China Univ. of Technol. Guangzhou 510640 China

AZ91 alloys were prepared by hot extrusion and its microstructure and tensile behavior at room temperature were investigated. Compared to as-cast ingot, the grain size of hot-extruded material is more refined, the intermetallic phase MgnAl12 is broken and dispersed discontinuously. Both streng.h and elongation of AZ91 are improved by hot extrusion. Tensile behavior and fracture surface of the experimental material were studied. Due to the change in microstructure, the fracture mech.nism of extruded material is different from that of as-cast ingot, the latter is mainly a brittle fracture. Ductile fracture plays a role in hot-extruded AZ91 failure at room temperature.

关键词： magnesium alloy hot extrusion microstructure tensile behavior

Thermal Oxidation Resistance of Rare Earth-Containing Composite Elastomer

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Journal of Rare Earths 2001年第3期19卷 192-197页

作者：邱关明张明周兰香中北里志井上真一冈本弘 Dept. of Mat. and Chem. eng. Coll. of Optics and Fine Mech. Changchun 130022 China

The rare earth-containing composite elastomer was obtained by the reaction of vinyl pyridine-SBR (PSBR) latex with rare earth alkoxides, and its thermal oxidation resistance was studied. After aging test, it is found that its retention rate of mech.nical properties is far higher than that of the control sample. The results of thermogravimetric analysis show that its thermal-decomposing temperature rises largely. The analysis of oxidation mech.nisms indicates that the main reasons for thermal oxidation resistance are that rare earth elements are of the utility to discontinue autoxidation chain reaction and that the formed complex structure has steric hindrance effect on oxidation.

关键词： rare earths composite elastomer thermal oxidation resistance discontinue autoxidation steric structure