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Excellent plasma electrolytic oxidation coating on AZ61 magnesium alloy under ordinal discharge mode

Journal of Magnesium and Alloys 2022年第9期10卷 2460-2474页

作者： Weiyi Zhang yunhui du Peng Zhang School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China

In the preparation of plasma electrolytic oxidation(PEO)coating,the rapid heating of freely-happened electron avalanche under traditional discharge(TD)mode inevitably results in a strong eruption of electric breakdown *** PEO coating is loose and invariably composed of a very thin inner dense layer and an outer loose layer,as a result of which its properties and application have been limited *** this work,for purpose of weakening the eruption of breakdown melt,thickening the inner dense layer,densifying the outer loose layer and improving the performance of PEO coating,ordinal discharge(OD)mode of PEO coating is developed by regulating the mass ratio of MgF_(2) to MgO(α)and voltage in the PEO investigation on AZ61 magnesium alloy in KF-KOH *** formation mechanism under different discharge mode,electrochemical corrosion and wear of PEO coatings are *** results show that the suitableαand voltage for effective OD are 1.3 and 130 V under which the freely-happened electron avalanche in MgF_(2) under TD mode can be restricted by the adequate adjacent *** with TD mode,the inner dense layer,in which the(10¯1)plane of MgF_(2) is parallel to the(111)plane of MgO at their well-knit semi-coherent interface,is thickened to 2.4∼7.2 times,the corrosion potential(E_(corr))improvement is enlarged to 3.6∼13.2 times and the corrosion current intensity(I_(corr))is reduced from 10.8∼9.499 to 0.433(10^(−6) A/cm^(2)).The outer loose layer is densified and the wear rate is lessened 65.5%∼89.8%by the evident melioration in surface porosity,impedance and *** work deepens the understanding about the discharge of PEO coating and provides an available OD mode for preparing excellent PEO coating.

关键词： Magnesium alloy Plasma electrolytic oxidation coating Ordinal discharge Microstructure Performance

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Radial Distribution of SiC Particles in Mechanical Stirring of A356-SiC_p Liquid

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Journal of Materials Science & Technology 2012年第10期28卷 951-955页

作者： yunhui du Peng Zhang Jun Zhang Shasha Yao School of Mechanical&Controlled Engineering Beijing Jiaotong UniversityBeijing 100044China

The mechanical stirring of A356-2.5 vol.% SiCp liquid was conducted in a cylindrical crucible by a straight-blade stirrer. The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25 deg. for gradient angle α of blade and 10 mm/s for speed of moving up and down of stirrer, The results show that there exists a nonlinear relationship between rotating speed of stirrer and radial relative deviation of SiCp content in A356 liquid between the center and the periphery of crucible. The greater the rotating speed of stirrer is, the bigger the radial relative deviation of SiCp content in A356 liquid becomes and the more nonhomogeneous the radial distribution of SiC particles in A356 liquid turns. In addition, when the rotating speed of stirrer is about 200 r/min, the vertical distribution of SiC particles in A356 liquid is relative uniform. It can be seen that the nonhomogeneous distribution of SiC particles in A356 liquid results from the nonhomogeneous radial distribution of SiC particles in A356 liquid in straight-blade mechanical stirring ultimately.

关键词： Radial distribution Straight-blade mechanical stirring Relationship

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Modeling and Optimizing of Deformed Steel Bars Hot Rolling

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International Journal of Minerals,Metallurgy and Materials 1999年第4期13卷 289-291页

作者： Peng Zhang yunhui du Xueping Ren(Material Science and Engineering School, University’ of Science and Technology’ Beijing, Beijing 100083) Material Science and Engineering School University of Science and Technology Beijing Beijing 100083 China

Based on experimental data, a nonlinear model about tensile strength and technical parameters such as Mn and St content, finishing rolling speed and finishing rolling temperature for deformed steel bars in the process of hot rolling was established by using artificial neural networks. The model can be optimized with a genetic algorithm. The optimum rolling parameters were obtained.

关键词： artificial neural networks modeling genetic algorithm, optimizing

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The Uniform Distribution of SiC Particles in an A356-SiC_p Composite Produced by the Tilt-blade Mechanical Stirring

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Acta Metallurgica Sinica(English Letters) 2013年第1期26卷 69-74页

作者： yunhui du Peng ZHANG Yujie WANG Jun ZHANG Shasha YAO Chengyu LI School of Mechanical & Controlled Engineering Beijing Jiaotong University

The tilt-blade mechanical stirring of A356-2.5vol.%SiCp liquid was conducted in a cylindrical crucible to solve the problem of nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring. The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25° for horizontal tilt angle α of the blade, 200 r/min for rotating speed of stirrer and 10 mm/s for speed of moving up and down of stirrer. The results show that there exists a nonlinear relationship between circumferential tilt angle β of the blade and radial relative deviation d of SiCp content in A356 liquid. When β is smaller than 20°, the d of SiCp content in A356 liquid between the center and the periphery of crucible decreases with increasing β. Conversely, when β is bigger than 26°, d increases with increasing β. Only when β is about 20°, d can be equal to nought i.e. uniform radial distribution of SiC particles can be realized. It can be seen that the nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring can be eliminated in this tilt-blade mechanical stirring of A356-SiCp liquid.

关键词： Tilt-blade mechanical stirring Relationship Uniform distribution

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Quick Surface Treatment of AZ31B by AC Micro-arc Oxidation

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Journal of Wuhan University of Technology(Materials Science) 2014年第4期29卷 773-779页

作者：王胜林张鹏 du yunhui WANG Yujie HAO Zhiqiang School of Mechanical & Controlled Engineering Beijing Jiaotong University

In order to explore an effective way to shorten treatment time and enhance the quality of treatment coating, AC micro-arc oxidation was conducted to treat the surface of AZ31 B deformation magnesium alloy in KF＋KOH treatment solution. The infl uences of micro-arc oxidation parameters such as concentration of KF, concentration of KOH, output voltage of booster, temperature of treatment solution, and treatment time on treatment coating thickness were raveled out under different conditions. The structure and composition of treatment coating were determined, the growth mechanism of treatment coating was discussed, and the quick surface treatment technology for compact treatment coating with maximum thickness was developed. The experimental results show that： A maximum 33 μm-thick compact treatment coating, consisting of MgF2 and MgO mainly, can be formed on AZ31 B in 112 s under the conditions of 1 132 g/L KF, 382 g/L KOH, 66 V for output voltage of booster and 34 ℃ of treatment solution which were optimized by a genetic algorithm from the model established by artifi cial neural networks. There are no ＂crater-shaped＂ pores in this treatment coating as the heat shock resulting from the smooth variation of AC sinusoidal voltage is far smaller than that of the rigidly varied DC or pulse current. The treatment time is only one sixth of that adopted in the other surface treatment technology at best, principally for the reason that the coating can always grow irrespective of the electric potential of AZ31 B. This investigation lays a fi rm foundation for the extensive application of magnesium alloy.

关键词： AZ31B deformation magnesium alloy quick surface treatment AC micro-arc oxidation

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Effect of Relative Reduction on Property of Steel-Mushy Cu-Graphite Composite

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Journal of Materials Science & Technology 2005年第4期21卷 589-592页

作者： Peng ZHANG yunhui du Hanwu LIU Daben ZENG Jianzhong CUI Limin BA Department of Mechanical Engineering Beijing 3iaotong University Beijing 100044 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China Metal Forming Department Northeastern University Shenyang 110004 China Anshan Automobile Fittings Factory Anshan 114014 China

The rolling treatment of steel-mushy QTi3.5-3.5 graphite composite was conducted under different relative reduction at room temperature. The effect of room-temperature rolling on interracial mechanical property of steel-mushy QTi3.5-3.5 graphite composite was studied and the relationship between interracial shear strength and relative reduction was established. The results show that, for steel-mushy QTi3.5-3.5 graphite composite, which consists of 1.2 mm-thick 08AI steel plate and 2.8 mm-thick QTi3.5-3.5 graphite layer, there is a nonlinear relationship between interracial shear strength and relative reduction in graphite layer. When relative reduction is smaller than 1.1%,interracial shear strength increases with increasing the relative reduction. When relative reduction is larger than 1.1%, interracial shear strength decreases with increasing the relative reduction. When relative reduction is 1.1%,the largest interracial shear strength of 145.2 MPa can be obtained.

关键词： Rolling Relative reduction Interracial shear strength Steel-mushy Cu-graphite composite

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Semi-solid Processing of Al-7Graghite Composite

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Journal of University of Science and Technology Beijing 2001年第3期8卷 203-206页

作者： Peng Zhang, yunhui du, Daben Zeng Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China Department of Mechanical Engineering Tsinghua University Beijing 100084 China

Al-7graphite composite was processed using Al-7graphite mushy prepared by electromagnetic-mechanical stirring method, and the influence of solid fraction on the distributing of graphite particles in ingot was studied. The results shows that the relationship between solid fraction and stirring temperature of mushy is: f(s) = 591.5-0.897 t (where f(s) is the solid fraction, t is the stirring temperature). For Al-7graphite composite, with the increasing of solid fraction, the aggregation extent of graphite particles reduced gradually, and when solid fraction was larger than 30%, graphite particles could distribute evenly in ingot.

关键词： Al-7graphite composite electromagnetic-mechanical stirring method distributing of graphite particles solid fraction stirring temperature

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Influence of Pressing Time on Steel-copper-graphite Bonding

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Journal of Materials Science & Technology 2006年第2期22卷 235-238页

作者： Peng ZHANG yunhui du Hanwu LIU Jun ZHANG Daben ZENG Jianzhong CUI Limin BA Department of Mechanical Engineering Beijing Jiaotong University Beijing 100044 China Department of Mechanical Engineering Tsinghua University Beijing 100084 China Metal Forming Department Northeastern University Shenyang 110506 China Anshan Automobile Fittings Factory Anshan 114014 China

The bonding of steel plate with QTi3.5-3.5 graphite slurry was studied by using pressing bonding technique. The influence of pressing time on the interracial mechanical property of bonding plate was researched. The results show that： under the conditions of 620℃ preheating temperature of steel plate, 530℃ preheating temperature of dies, 46% solid fraction of QTi3.5-3.5 graphite slurry and 50 MPa pressure, there exists a nonlinear relationship between pressing time and interracial shear strength. The interracial shear strength of bonding plate increases with increasing pressing time and reaches a largest value about 127 MPa when pressing time is longer than 120 s. At the interface with the best mechanical property, there exists a continuous Fe-Cu inter-diffusion zone and a metallurgical bonding.

关键词： Steel-copper-graphite bonding Pressing time Interracial shear strength

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Influence of stirring speed on SiC particles distribution in A356 liquid

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China Foundry 2012年第2期9卷 154-158页

作者： Yao Shasha Zhang Peng du yunhui Zhang Jun Lu Xiaopeng School of Mechanical&Controlled Engineering Beijing Jiaotong UniversityBeijing 100044China

A straight-blade mechanical stirrer was designed to stir A356-3.5vol%SiCp liquid in a cylindrical crucible with the capability of systematically investigating the influence of rotating speed of stirrer on the distribution of SiC particles in A356 liquid. The experimental results show that the vertical distribution of SiC particles in A356 liquid can be uniform when the rotating speed of stirrer is 200 rpm, but the radial distribution of SiC particles in A356 liquid is always nonhomogeneous regardless of the rotating speed of stirrer. The radial centdfugalization ratio of SiC particles in A356 liquid between the center and the periphery of crucible increases with the rotating speed of stirrer. The results were explained in the light of SiC particles motion subject to a combination of stirring and centrifugal effect.

关键词： straight-blade mechanical stirring influence centrifugalization distribution SiC particles

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Spatial Correlation and Ecological Characteristics Analysis of Man-agement Area for Biodiversity Conservation and Relevant Regionalization

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Chinese Geographical Science 2014年第1期24卷 71-82页

作者： WANG Wenjie ZHENG Hua XU Chao JIANG Weiguo du yunhui WANG Wei ZHANG Zhe LIU Xiaofu Chinese Research Academy of Environmental Sciences Key Laboratory of Systems Ecology Research Center for Eco-Environmental SciencesChinese Academy of Sciences State Key Laboratory of Earth Surface Processes and Resource Ecology Beijing Normal University Appraisal Center for Environment&Engineering Ministry of Environmental Protection

Formulation of different ecological zone plans according to the corresponding protection targets and the necessity of proper conservation policy is one of the measures to achieve the goal of ecological conservation in *** order to clarify the interrelation among key ecological zone plans,this paper carried out the research on spatial relation of priority areas of biodiversity conservation and three key ecological areas(key ecological function areas,key regions of ecological service function,national nature reserves)and the research on ecological conditions,based on multi-scale ecological spatial theme information,which incorporates elements like ecological quality and type,and by the aid of spatial information analysis and GIS *** results showed a contrastively fine spatial consistency with 68.8%of priority areas of biodiversity conservation overlapping with three key ecological *** the environment in priority areas of biodiversity conservation were in good conditions,protection pressure is also increasing,powerful supervision and protection should not be *** environmental conditions in the overlapping areas,as a whole,were superior to those in the non-overlapping *** two areas have different characteristics,targeted protection measures should be formulated based on this difference,which will be very important for biodiversity conservation in priority areas of biodiversity conservation.

关键词： biodiversity conservation ecological regionalization ecological pressure ecological service spatial correlation analysis

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