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Research on microstructure in as-cast 7A55 aluminum alloy and its evolution during homogenization

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Rare Metals 2011年第6期30卷 664-668页

作者： LV Xinyu guo erjun LI Zhihui WANG guojun The School of Materials Science and Engineering Harbin University of Science and Technology Harbin 150080 China Northeast light alloy Co. Ltd. Harbin 150060 China State Key Laboratory of Nonferrous Metals and Processes General Research Institute for Nonferrous Metals Beijing 100088 China

The microstructure of the as-cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and differential scanning calorimetry （DSC） analysis. The results indicate that the microstructure of the as-cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AIZnMgCu eutectic phases, and intermetaUic compounds MgZn2, Al2CuMg, Al7Cu2Fe, and Al23CuFe4. After homogenization at 470℃ for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting-point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy The high melting-point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470℃/72 h.

关键词： 7A55 aluminum alloy as-cast constituents homogenization

Rotary impeller refinement of 7075Al alloy

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Rare Metals 2009年第3期28卷 309-312页

作者： WANG Liping guo erjun HUANG Yongchang LU Bin School of Materials Science and Engineering Harbin University of Science and Technology Harbin 150080 China

The effects of four parameters, gas flow, rotational speed, refining time, and stewing time, on the rotary impeller refinement of 7075 Al were studied. The effects of C2Cl6 refining, rotary impeller refining, and composite refining of 7075 Al alloy were compared with each other. The results showed that the greatest impact parameter of rotary impeller refinement was rotational speed, followed by gas flow, refining time, and stewing time. The optimum purification parameters obtained by orthogonal analysis were as follows： rotor speed of 400 r/min, inert gas flow of 0.4 mL/h, refining time of 15 min, and stewing time of 6 min. The best degassing effect can be obtained by the composite refining of C2Cl6 and rotary impeller. The degassing rate of C2Cl6, rotary impeller, and composite refining was 34.5%, 69.2%, and 78%, respectively. The mechanical properties of the specimen refined by rotary impeller were higher than those by C2Cl6 refining, but lower than those by composite refining.

关键词： aluminum alloys refinement technology processing parameters mechanical properties

Effect of Bi on graphite morphology and mechanical properties of heavy section ductile cast iron

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China Foundry 2014年第2期11卷 125-131页

作者： Song Liang guo erjun Tan Changlong School of Materials Science and Engineering Harbin University of Science and Technology

To improve the mechanical properties of heavy section ductile cast iron, bismuth(Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidifi cation cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the fi ve castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture.

关键词： heavy section ductile cast iron Bi addition cooling rate graphite morphology mechanical properties

Effects of RE,V,Ti and B composite modification on the microstructure and properties of high chromium cast iron containing 3% molybdenum

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Rare Metals 2009年第6期28卷 606-611页

作者： guo erjun WANG Lihua WANG Liping HUANG Yongchang School of Materials Science and Engineering Harbin University of Science and Technology Harbin 150080 China

The effects of RE, V, Ti and B on the microstructure and properties of high chromium cast iron containing 3% molybdenum under as-cast and heat treatment conditions were investigated with the method of comparing experiments. The results show that with the increase of RE content, the primary austenite of high chromium cast iron is obviously refined. The morphology of carbide is changed from netlike and lath to small multiangular isolated blocks or massive blocks, the isolated degree of carbide is improved obviously, and the size is significantly refined. The addition of V and B into high chromium cast iron can refine the microstmcture, reduce coarse columnar crystals and make the carbide smaller and uniform. Through composite modification with RE, V, Ti and B, the hardness, wear resistance and impact toughness of high chromium cast iron are increased conspicuously. After heat treatment, the hardness of high chromium iron is increased significantly, but the toughness and wear resistance do not show great improvement.

关键词： high-chromium cast iron rare earth composite modification microstructure mechanical properties

Influences of different degassing processes on refining effect and properties of 4004 Al alloy

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China Foundry 2013年第2期10卷 104-107页

作者： Wang Liping Cao guojian guo erjun Wang guojun Lü Xinyu School of Materials Science and Engineering Harbin University of Science and Technology China Northeast Light Alloy Co. Ltd.

In order to improve the plasticity of 4004 Al alloy and subsequently the productivity of 4004 Al foil, the research studied in detail the influence of the rotary impeller degassing process on the refining effect of 4004 Al alloy, in which the impacts of four major parameters: gas flow, rotational speed, refining time, and stewing time, on degassing rate of 4004 Al alloy was systematically studied by using an orthogonal experiment methodology. Results show that the rotational speed has the greatest impact on the degassing of 4004 Al alloy, followed by gas flow and refining time; stewing time has the least impact. The optimum purification parameters obtained by current orthogonal analysis were: rotor speed of 500 r·min-1, inert gas flow of 0.4 mL·h-1, refining time of 15 min, and stewing time of 6 min. Degassing rate using the optimum parameters reaches 68%. In addition, the comparison experiments among C2Cl6 refining, rotary impeller degassing, and combined treatment of C2Cl6 refining and rotary impeller degassing for 4004 Al alloy were performed. The experimental data indicated that the combined treatment of C2Cl6 refining and rotary impeller degassing has the best degassing effect. Degassing rate of C2Cl6 refining, rotary impeller degassing and combined refining treatment is 39%, 69.1% and 76.9%, respectively. The mechanical properties of the specimen refined by rotary impeller degassing were higher than those by C2Cl6 refining, but lower than those by combined refining treatment.

关键词： aluminum alloys refinement technology rotary impeller degassing

Tribological properties of copper matrix composites reinforced with homogeneously dispersed graphene nanosheets

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Journal of Materials Science & Technology 2018年第10期34卷 1925-1931页

作者： Xin Gao Hongyan Yue erjun guo Shaolin Zhang Longhui Yao Xuanyu Lin Bao Wang Enhao Guan School of Materials Science and Engineering Harbin University of Science and Technology Department of Physics Dongguk University

Graphene reinforced copper matrix composites （Gr/Cu） were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3 wt~ Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.

关键词： Graphene nanosheets Copper matrix composites Tribological properties Microstructure

Physical modeling of spent-nuclearfuel container

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China Foundry 2012年第4期9卷 366-369页

作者： Wang Liping guo erjun Jiang Wenyong Xue Muyu Liu Dongrong Ren Shanzhi School of Materials Science and Engineering Harbin University of Science and TechnologyHarbin 150040China School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001China

A new physical simulation model was developed to simulate the casting process of the ductile iron heavy section spent-nuclear-fuel *** this physical simulation model,a heating unit with DR24 Fe-Cr-Al heating wires was used to compensate the heat loss across the non-natural surfaces of the sample,and a precise and reliable casting temperature controlling/monitoring system was employed to ensure the thermal behavior of the simulated casting to be similar to the actual ***,a mould system was designed,in which changeable mould materials can be used for both the outside and inside moulds for different *** casting test was carried out with the designed mould and the cooling curves of central and edge points at different isothermal planes of the casting were *** show that for most isothermal planes,the temperature control system can keep the temperature differences within 6 ℃ between the edge points and the corresponding center points,indicating that this new physical simulation model has high simulation accuracy,and the mould developed can be used for optimization of casting parameters of spent-nuclear-fuel container,such as composition of ductile iron,the pouring temperature,the selection of mould material and design of cooling *** addition,to maintain the spheroidalization of the ductile iron,the force-chilling should be used for the current physical simulation to ensure the solidification of casting in less than 2 h.

关键词：计算机仿真计算机模拟铸造铸造工艺

Efect of residual Al content on microstructure and mechanical properties of Grade B+Steel for castings for locomotives

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China Foundry 2013年第6期10卷 391-395页

作者： Wang Kaifeng guo erjun Cao guojian Wang Liping Feng Yicheng Jiang Wenyong Tao Chunguo College of Materials Science and Engineering Harbin University of Science and Technology Qiqihar Railway Rolling Stock (Group) Co. Ltd.

The bogie made of Grade B+ steel is one of the most important parts of heavy haul trains. Some accidents were found to be the result of fracture failure of the bogies. It is very important to find the reason why the fracture failure occurred. Because Al was added for the final deoxidation during the smelting process of the Grade B+Steel, residual Al existed to some extent in the castings. High residual Al content in the bogie casting was presumed to be the reason for the fracture. In this work, the influence of residual Al content in the range of 0.015wt.% to 0.3wt.% on the microstructure and mechanical properties of the Grade B+ Steel was studied. The experimental results showed that when the residual Al content is between 0.02wt.% and 0.20wt.%, the mechanical properties of the steel meet the requirements of technical specification for heavy haul train parts, and the fracture is typical plastic fractures. If the residual Al content is less than 0.02wt.%, the microstructures are coarse, and the mechanical properties can not meet the demand of bogie steel castings. When the residual Al content is more than 0.2wt.%, the elongation, reduction of area, and low-temperature impact energy markedly deteriorate. The fracture mode then changes from plastic fracture to cleavage brittle fracture. Therefore, the amount of Al addition for the final deoxidation during the smelting process must be strictly controlled. The optimum addition amount needs to be controlled within the range of 0.02wt.% to 0.20wt.% for the Grade B+Steel.

关键词： bogie Grade B+Steel Al content mechanical properties

Zero thermal expansion in Cs_(2)W_(3)O_(10)

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Chinese Chemical Letters 2024年第7期35卷 538-541页

作者： Juan guo Mingyuan Fang Qingsong Liu Xiao Ren Yongqiang Qiao Mingju Chao erjun Liang Qilong Gao School of Physics&Microelectronics Key Laboratory of Materials Physics of Ministry of Education of ChinaZhengzhou UniversityZhengzhou 450052China

Zero thermal expansion materials are important for the practical applications due to their shape stability as changing *** reported concept of average atomic volume is an available method to hunt new zero thermal expansion ***,according to this concept,a tetragonal tungstate Cs_(2)W_(3)O_(10)with zero expansion has been *** is no structure phase transition as increasing temperature from 150 K to 573 *** coefficient of thermal expansion of axes and volume areαa=0.0074×10^(-6)K^(-1),αc=1.63×10^(-6)K^(-1),andαV=1.60×10^(-6)K^(-1),respectively,in the temperature range of 150~573 *** temperature-and pressure-dependent Raman spectra reveal that the vibrations of WO6octahedra libration modes with positive total anharmonicity and W-O-W bending mode with negative Grüneisen parameter are possibly the origin of zero thermal expansion in Cs_(2)W_(3)O_(10).

关键词： Zero thermal expansion Cesium tungstate Raman spectra Average atomic volume Temperature-dependent X-ray diffraction