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      20 May 2012, Volume 0 Issue 5 Previous Issue    Next Issue
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    Microstructure and Mechanical Properties of As-cast Mg-Zn-xCu-Ce Alloys
    HU Yao-bo, ZHAO Chong, WU Fu-zhou, LI Ya-ni
    2012, 0 (5): 1-5.  
    Abstract ( 905 ( PDF (2634KB)( 451 Citation
    The effect of Cu element on microstructure and mechanical properties of as-cast Mg-Zn-xCu-Ce alloy was investigated by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers-hardness tester. The results show that the grain size significantly refines from 135μm to 86μm with Cu added. In the case of Cu mass fraction less than Zn, the thin layer of eutectic phases comprises α-Mg and CuMgZn at interdendritic. The Mg2Cu second phase appears in eutectic and the microstructure of eutectic phases begins to coarsen when Zn, Cu mass ratio equals to 1 With the content of Cu further increases (mass fraction of Cu greater than Zn), eutectic (α-Mg+CuMgZn+Mg2Cu) forms at interdendritic, and eutectic changes thin layer into the honeycomb on morphology. The microhardness of as-cast alloy increases with Cu added.
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    Effects of Nd:YAG Laser Welding on Microstructure and Texture of Aluminum-lithium Alloys
    CUI Li, LI Xiao-yan, HE Ding-yong, CHEN Li, GONG Shui-li
    2012, 0 (5): 6-9.  
    Abstract ( 821 ( PDF (2355KB)( 419 Citation
    5A90 aluminum-lithium (Al-Li) alloy thin sheets, machined with a square butt weld preparation, were welded by Nd:YAG laser. Microstructure and texture characterization in the laser welds were studied by means of optical microscope (OM), scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), electron back scattered diffraction (EBSD), and compared with the unaffected base metal. The results show that the weld metal (WM) microstructure is displayed significant changes in solidification structure, and microtexture. The predominantly fine equiaxed dendritic microstructure in the WM zone is observed and rationalized on the basis of solidification mechanism and heterogeneous nucleation mechanism. The pole figures of 5A90 Al-Li sample exhibit a typical cold rolling textures structure of FCC metals, while the laser welds in 5A90 Al-Li alloys are shown to exhibit a randomly textured microstructure.
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    Simulation of Optimum Parameter in Horizontal Planetary Ball Mill
    ZHU Fei, ZHANG Lin-jin, CAI Dao-lin, YE Xu-chu
    2012, 0 (5): 10-14.  
    Abstract ( 765 ( PDF (2252KB)( 331 Citation
    Simulation of the mean contact force of grinding balls in the horizontal planetary ball mill and relation between the mean contact force and factors including ball filling ratio, grinding ball diameter, milling pot radius and revolution radius were done using the distinct element method for particle system, and with the experimental results for comparative analysis. The results show that the grinding rate of the horizontal planetary ball mill can be determined by the mean contact force, logarithm of the grinding rate is linear function about the mean contact force and the gradient is 0.087. With fill rate increasing, the mean contact force of grinding balls decreases gradually; the mean contact force of grinding balls increases linearly with the grinding ball diameter, milling pot radius and revolution radius, and the gradient is 2.5, 0.14 and 0.03 respectively, the grinding ball diameter is primary factor, meanwhile.
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    Pitting Mechanism for Aluminum Electrolytic Capacitor High Voltage Foil
    WANG Zhi-shen, HE Ye-dong, SUN Zhi-hua, LIU Ming, ZHANG Xiao-yun, LU Feng
    2012, 0 (5): 15-19.  
    Abstract ( 734 ( PDF (3774KB)( 305 Citation
    Pitting mechanism for aluminum electrolytic capacitor high voltage foil in strong acidic solution was investigated by means of polarization curve and scanning electron microscopy(SEM). The results indicate that pitting can generate on the surface of Al foil under open circuit, and its corrosion potential measured is pitting potential. Pitting potential appears on the polarization curves of Al foil with tunnel pits, and there is linear relationship between the pitting over-potential and the tunnel length. According to micro-cell model of pitting and the corrosion polarization diagrams of micro-cell, it is thought that the surface of Al foil with tunnel pits transforms from cathode to anode during anodic polarization, and the critical point of the transformation is the measured pitting potential.
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    Wear Resistance of In-situ Fe-Cr-V-C Hardfacing Alloys Fabricated by Plasma Transferred Arc Weld-surfacing Process
    ZONG Lin, LIU Zheng-jun, LI Le-cheng
    2012, 0 (5): 20-23.  
    Abstract ( 781 ( PDF (8940KB)( 395 Citation
    Fe-Cr-V-C hardfacing alloys with different Cr contents were prepared under plasma transferred arc (PTA). The phases constitution, carbide morphology were investigated by means of scanning electron microscopy(SEM) and X-ray diffraction(XRD). The effect of Cr contents on the wear resistance of hardfacing alloys was detected by using Rockwell hardometer and wear testing machine. In addition, the abrasion wear mechanism was discussed. The results show that the microstructure consists of martensite, ferrite and austenite, carbides such as primary M7C3, VC. As the Cr contents increase, the wear resistance first decreases because of the little changes of content and morphology for M7C3 and VC hard phases and the decrease of acicular martensite with high hardness, afterwards, the wear resistance increases when Cr content reaches a particular value as a result of the increase of M7C3 contents. When Cr mass fraction is 27.2%, a high volume fraction of hexagonal (Fe,Cr,V)7C3 complex carbides and a small amount globular VC particles in the microstructure form a substantial wear resistant structure, which leads to an excellent wear resistance.
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    Structure and Wear Properties of Plasma Sprayed Al2O3-30%TiO2 Micro/Nano-composite Coatings
    YI De-liang, YE Yin-ping, LIU Guang, YIN Bin, ZHOU Hui-di, CHEN Jian-min
    2012, 0 (5): 24-29.  
    Abstract ( 1010 ( PDF (3978KB)( 431 Citation
    Al2O3-30%(mass fraction)TiO2 nanocomposite powders with different particle sizes were synthesized by sol-gel method. The nano-powders were then spray dried, and series of Al2O3-TiO2 composite coatings were prepared by plasma spraying using the spray dried powders, the coatings’ structure was characterized and performance was tested. The analysis results on the morphologies and structures of the composite coatings indicate that the prepared coatings have micro/nano-composite structures and the initial powders’ particle size has little impact on the coatings’ structure and density. The friction and wear properties of the coatings indicate that the wear rate decreases with the increasing of the initial particle size. The micro/nano-composite coating deposited by powder with particle size of 100nm has the minimum wear rate. The wear mechanism of the Al2O3-30%TiO2 micro/nano-composite coating is mainly due to the spalling caused by crack propagation.
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    Effect of Deposition Time on Microstructures and Properties of ZrTiN coatings
    YAN Pei, DENG Jian-xin, LIAN Yun-song, ZHAO Jun, CHEN Zhen
    2012, 0 (5): 30-34.  
    Abstract ( 915 ( PDF (2375KB)( 423 Citation
    Multi arc ion plating ZrTiN hard coatings were deposited on WC/TiC/Co and WC/Co cemented carbide substrate with independent Ti and Zr targets. The effect of deposition time on morphology, phase composition, thickness, hardness and adhesive strength of the coatings was investigated, respectively. The results show that only face centered cubic structure phase forms in the coatings and the crystal orientation maintains (111). Grain size of the coating is around 10nm without changing during experimental process. Microhardness and adhesive strength of the coatings decline evidently when deposition time is 120min.
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    Influence of Initial Stress on Surface Stress Measurement of 45 Steel by Rayleigh Wave
    LIU Bin, DONG Shi-yun, XU Bin-shi, HE Peng, YAN Shi-xing
    2012, 0 (5): 35-38.  
    Abstract ( 696 ( PDF (1226KB)( 342 Citation
    Based on Rayleigh wave acoustoelastic theory, surface stress measurement of 45 steel and the influence of initial stress state on stress measurement were introduced. Two Rayleigh wave transducers with 5MHz frequency, the fixed distance, were employed to detect the surface of 45 steel as an emitter and a receiver. The difference in time of flight between free loaded signal and loaded signal corresponding to different tensile stress was determined with normalized cross correlation function. Results show that the influence of initial stress state on relationship between propagation velocity of Rayleigh wave and tensile stress is faint, the propagation velocity of Rayleigh wave increases linearly with tensile stress increasing, when tensile stress attains a value, the relationship between velocity of Rayleigh wave propagating in the surface of 45 steel and tensile stress is nonlinear further. Nominal Rayleigh wave acoustoelastic coefficients corresponding to different initial stress state of 45 steel are obtained, and they are 0.838 and 1.041, respectively.The stress corresponding to the maximum difference in time of flight is also different, the relative error of stress measurement corresponding to different initial stress state is about 22%.
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    Defect Quantitative Identification and Image Reconstruction Based on Thermal Wave Inspection
    SONG Yuan-jia, ZHANG Wei, WANG Dong-dong, TIAN Gan, JIN Guo-feng
    2012, 0 (5): 39-46.  
    Abstract ( 672 ( PDF (6571KB)( 313 Citation
    Debond defects between shell and insulation layer of solid rocket motor (SRM) were inspected by numerical analysis and experiment based on thermal wave nondestructive testing (TWNDT) technique. In order to gain intuitionistic and accurate image of defects, the homomorphic filtering was used to enhance the image quality and the particle swarm optimization fuzzy clustering method (PSO-FCM) was applied to segment the defect. Then the size and depth were estimated quantificationally. On this basis, the defects can be 3D reconstructed by volume rendering. The results show that homomorphic filtering has higher peak signal to noise ratio(PSNR)and can improve image quality; the PSO-FCM can achieve the better effect of image segmentation; it could be detected quantitatively and 3D reconstructed effectively for the defects, which establish basis for future research of defect auto-identification.
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    Fatigue Model for Foamed Metals with High Porosity and Corresponding Experimental Study
    LIU Pei-sheng, MA Xiao-ming
    2012, 0 (5): 47-53.  
    Abstract ( 754 ( PDF (21283KB)( 292 Citation
    In the light of the simplified structural model of open-cell foamed metals with high porosity, the bearing structure-fatigue model was established for this type of materials under cyclic loading by force analysis, and the evaluating index was derived for the corresponding fatigue property. Based on the above mentioned model, the fatigue property of this type of materials was experimentally studied with the index from this model to evaluate the fatigue property of the nickel foam with open-cell structure. Using two sorts of loading experiments of pressing-pressing and bending cycles, the obtained index weighing the fatigue property was validated to be feasible. The results show that the similar stress fatigue property decreases when the porosity increases for the nickel foam under loading cycle of pressing-pressing, but the similar strain fatigue property is improved when the porosity increases and the pore diameter decreases for this experimental material under cyclic bending loading.
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    Microstructure of FSW Joint of Die-casting AZ91D Magnesium Alloy
    YOU Guo-qiang, ZHANG Jun-cheng, WANG Xiang-jie, CHEN Yong
    2012, 0 (5): 54-58.  
    Abstract ( 1111 ( PDF (2457KB)( 985 Citation
    Die casting plates of AZ91D magnesium alloy, with thickness of 4mm, were welded by friction stir welding,with a rotating speed of 1500r/min and welding speed of 120mm/min. The joint microstructure was studied by OM and SEM.The results show that the appearance of the welding joint is good, but there is a tunnel defect in the joint. The joint microstructure exhibits noticeable deformation characteristics: the grains of weld nugget zone are fine and recrystallized.Thermo-mechanically affected zone shows partially recrystallized microstructure. The microstructure of heat affected zone is similar to that of the base metal while the grains are a little coarser. Moreover, the transition between the weld nugget zone and the thermo-mechanically affected zone in the advancing side is discontinuous, while that in the retreating side is gradient.
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    Effects of Dieless Drawing Processing Parameters on Microstructure and Mechanical Properties of Silicon Bronze
    WANG Zhen, LIU Xue-feng, HE Yong, XIE Jian-xin
    2012, 0 (5): 59-63.  
    Abstract ( 717 ( PDF (1932KB)( 328 Citation
    QSi3-1 silicon bronze alloy wires were processed by dieless drawing with the feeding speed of 0.5mm?s-1, the drawing speed of 0.67-1.00mm?s-1 and the heating temperature of 600-800℃. Effects of drawing speed and heating temperature on microstructure and mechanical properties of the alloy were investigated. The results show that the average grain size of the alloy after dieless drawing is larger at a high heating temperature when the drawing speed and area reduction are given, while it is finer at a high drawing speed when the heating temperature is constant. The hardness and tensile strength of the alloy decrease rapidly at first and then slowly with the increase of heating temperature. Meanwhile, they increase slightly with increasing the drawing speed. The grains of the alloy undergo deformation refinement and subsequently swallowing up each other at a high temperature during dieless drawing process.
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    Comparative Analysis on Defects in Repeated Upsetting and Stretching Deformation with Extrusion Deformation of FGH96 Alloy
    ZHANG Min-cong, WANG Shu-yun, XIONG Hua-ping, CAO Chun-xiao, LIU Chen-yi, DONG Yun-peng
    2012, 0 (5): 64-69.  
    Abstract ( 782 ( PDF (3378KB)( 322 Citation
    The inclusion defects in repeated upsetting and stretching deformation and hot extrusion(HEX) deformation of FGH96 alloy were compared and the deformation characteristics of non-metallic inclusions were studied. The results show that the quantity of non-metallic inclusions which can be detected in forging increases variously and over-standard defects are multiplied in repeated upsetting and stretching process of FGH96 alloy. Moreover, the quantity of non-metallic inclusions which can be detected in forging reduces obviously and cleanliness level rises largely in HEX+HIF(Hot Isothermal Forging) process of FGH96 alloy. The sizes in the direction perpendicular to deformation of non-metallic inclusions increase in isothermal forging process. The non-metallic inclusions in repeated upsetting and stretching process get together and areas of inclusions increase. The non-metallic inclusions are pulled into a discontinuous line in extrusion direction and areas of inclusions in each direction are constricted in extrusion process of FGH96 alloy. The deformation characteristics of inclusions in HEX+HIF process of FGH96 alloy is conditioned by the state of the inclusions in extrusion process. In summary, extrusion process of large extrusion ratio can break the non-metallic inclusions in FGH96 alloy effectively and improve forging quality.
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    Influences of Processing Parameters on Reciprocating Extrusion Process of AZ31 Magnesium Alloy
    LIU Jun, GUO Xue-feng, ZHANG Zhong-ming, YE Yong-nan
    2012, 0 (5): 70-75.  
    Abstract ( 766 ( PDF (4744KB)( 457 Citation
    The rigid visco-plastic finite element method was used for the study on the coupling thermal-mechanical numerical simulation of reciprocating extrusion process of AZ31 magnesium alloy. The influence of initial temperature of blank, extrusion velocity and friction factor on the equivalent strain, equivalent stress and temperature field of reciprocating extrusion process was investigated. The results show that the extrusion velocity has little effect on the peak value of equivalent strain, with the increasing of the extrusion velocity, the peak value of temperature within the workpiece ascends linearly, the temperature distribution becomes more inhomogeneous, while the peak value of stress first increases and then decreases. With the increasing of initial blank temperature, the peak value of equivalent stress decreases linearly; and the friction factor has little effect on the peak value of temperature; with the increasing of friction factor, the peak value of equivalent strain first increases and then remains stable, and the peak value of equivalent stress increases with decreasing amplitude.
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    Influence of Pulse Current Auxiliary Sintering and Hot-pressed Sintering on Microstructures and Mechanical Behavior of NiAl-Al2O3 Composite
    XU Gui-hua, LU Zhen, ZHANG Kai-feng
    2012, 0 (5): 76-80.  
    Abstract ( 868 ( PDF (2520KB)( 343 Citation
    NiAl-Al2O3 composite was synthesized by mechanical alloying, and further consolidated by pulse current auxiliary sintering (PCAS) and hot-pressed sintering (HPS) respectively. The mechanical behavior of sintered compacts was evaluated, and the influences of sintering methods on microstructures and mechanical behavior were analyzed from the perspective of sintering mechanisms. The results indicate that, compared with those sintered by HPS, the compact fabricated by PCAS has a higher density and finer grain, and its Al2O3 particles are remarkably spherized. The compact fabricated by PCAS shows not only higher room-temperature compressive yield strength, but also higher elevated-temperature compressive yield strength. Meanwhile, its room-temperature compressive plasticity and fracture toughness are much higher than that of the compact fabricated by HPS.
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    Influences of Synergistic Pretreatment with Microwave and Calcium Oxide on Water Loss Rate and Accessibility of Plant Fibers
    CHEN Xiao-chuan, LIU Min-yi, XIAO Li-ren, CHEN Rong-guo, CHEN Qing-hua
    2012, 0 (5): 81-86.  
    Abstract ( 702 ( PDF (1313KB)( 288 Citation
    Two plant fibers, i.e. hell-tong fiber and water hyacinth fiber, were sequentially pretreated by high-speed kneading with calcium oxide and microwave radiating to help them to be applicable to wood plastic composites (WPC). The influences of synergistic pretreatment condition of microwave and calcium oxide on the water loss rate and the accessibility of plant fibers were studied by investigating and analyzing the water loss rate, the water retention value and IR spectra of plant fibers. The variational rule of the change of accessibility along with the change of microwave irradiation time was mainly discussed for the two plant fibers. Moreover, a possible dehydration mechanism was proposed to the plant fibers that were synergistically pretreated with calcium oxide and microwave. The results show that synergistic pretreatment with microwave and calcium oxide can notablely postpone the dehydration of plant fibers and decrease their water loss rate as their accessibility is improved after the pretreatment.
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    Recent Progress of High-dielectric-constant Polymer Composites
    SHANG Ji-wu, ZHANG Yi-he, LU Feng-zhu
    2012, 0 (5): 87-92.  
    Abstract ( 1796 ( PDF (876KB)( 1528 Citation
    The main problems in high-dielectric-constant polymer composites are reviewed. The composites of polymers with ceramics, conductive particles (metal particles, graphite and carbon nanotubes) are summarized. The review also narrates copper phthalocyanine and polyaniline modified all-organic high-K composites. Meanwhile, problems facing the traditional high-K polymer composites are discussed. At last, the prospects of the possible developments in the future are proposed, that is to enhance the dielectric constant, energy density, and to decrease the dielectric loss and production cost.
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    Progress of Thermal Spray Cermet Coatings
    LI Zhuo-xin, ZHU Hong-bin, LI Hui, SUN Ri-chao
    2012, 0 (5): 93-98.  
    Abstract ( 940 ( PDF (8264KB)( 394 Citation
    The research progress in preparation, microstructure and comprehensive properties of cermet coatings is reviewed from three factors: spray technique, powder characteristic and spraying parameters. The three factors control the degradation, oxidation of the ceramic phase and deposition behavior of composite powders together, and they affect the microstructure, mechanical property and tribological property consequently. On the basis of these studies, choosing the appropriate spray technique, composite powders and spray parameters is the key to obtaining cermet coatings with excellent performance.
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