20 November 2017, Volume 41 Issue 11
    

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  • Hot Deformation Induced Multi-scale Microstructure Effect in High-performance Bismuth Telluride Based Thermoelectric Material
    ZHAI Renshuang, WU Yehao, ZHU Tiejun, ZHAO Xinbing
    Materials For Mechanical Engineering. 2017, 41(11): 1-12,18. https://doi.org/10.11973/jxgccl201711001
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    The preparation methods and intrinsic properties of bismuth telluride based alloy were briefly introduced. The multi-scale microstructure induced by hot deformation in bismuth telluride based alloy, including atom-scale intrinsic point defects, lattice line defects, nano-scale lattice distorted regions, micro-scale texture and grains were summarized. The effect of the multi-scale microstructure on thermoelectric properties of bismuth telluride based alloys was reviewed.
  • Electrochemical Behavior and Discharge Performance of AZ31 Magnesium Alloy in Al(NO3)3 Solution
    XIA Xingyan, ZHANG Ya, SUN Yingdi, ZHOU Xuehua, CHEN Qiurong, ZHANG Tengfei
    Materials For Mechanical Engineering. 2017, 41(11): 13-18. https://doi.org/10.11973/jxgccl201711002
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    The electrochemical behavior and discharge performance of AZ31 magnesium alloy in different concentration of Al(NO3)3 solution were investigated by the testing and analysis of hydrogen evolution, open circuit potential, potentiodynamic polarization curve, alternating current impedance and constant-current discharge performance. The results indicate that with the increase of concentration of Al(NO3)3 solution, the open circuit potential and the free corrosion potential shifted negatively, the alternating current impedance decreased and the electrochemical activity enhanced. Compared with magnesium salt solutions, AZ31 magnesium alloy had higher constant current discharge voltage, more stable discharge curve, higher discharge efficiency and larger discharge capacity in 0.6 mol·L-1 Al(NO3)3 solution. 2Mg(OH)2·Al(OH)3 was generated on the surface of the AZ31 magnesium alloy electrode in the progress of discharge which promoted the Mg(OH)2 to fall off from electrode surface easily and helped the electrolyte contact with the electrode surface. The AZ31 magnesium alloy electrode had high discharge activity and discharge stability.
  • CNTs/Al Interfacial Reaction Degree and the Relationship with Mechanical Performance of Composite
    LI Zhongwen, LIN Renbang, HU Li, YU Ziyun, YAN Laipeng, TAN Zhanqiu, FAN Genlian, LI Zhiqiang, ZHANG Di
    Materials For Mechanical Engineering. 2017, 41(11): 19-22,28. https://doi.org/10.11973/jxgccl201711003
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    The evolution of interfacial reaction degree with different sintering time of mass fraction 2% CNTs/5083Al composite was studied by the electrochemical dissolution-gas chromatography method. The relationship of interfacial reaction degree and mechanical performance was discussed. The results show that with sintering time increasing from 1 h to 6 h, interfacial reaction degree of 2%CNTs/5083Al composite increased from 5.5% to 24.1% and showed a certain linear relationship with sintering time when the composite was sintered at 570℃. Young's modulus, yield strength and tensile strength of the composite increased at first and then decreased, while the elongation decreased slightly at first and then increased continuously with the increase of sintering time.
  • Microstructure and Performance of SnO2-C Composite Coating with Network Structure Used for Lithium Ion Batteries Anode
    WANG Na, YANG Qi, CUI Shuai, YANG Lu
    Materials For Mechanical Engineering. 2017, 41(11): 23-28. https://doi.org/10.11973/jxgccl201711004
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    The dimethylformamide (DMF) solution containing SnCl2, polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) was coated on the surface of Cu foils by simple knife coating, and then calcined in vacuum. The SnO2-C composite coating with three dimensional network structure was fabricated successfully. The micro-structure of the composite coating was characterized and the performance of network structure SnO2-C composite coating as lithium ion batteries anode was tested. The results show that the coating presented the continuous network structure formed by interconnected carbon based branches with width of 0.1-1 μm which consisted of amorphous carbon matrix, SnO2 nano-particles with size of 10-150 nm and micro-pores with size of 1-5 nm. When the composite coating was employed as anodes of lithium ion batteries, after 100 times cycling under current density of 50 mA·g-1, the composite coating electrodes exhibited specific capacity of 642 mAh·g-1 without capacity fading during the cycling. The specific capacity of the electrodes under current density of 10 A·g-1 was 43% of the specific capacity under current density of 50 mA·g-1. The composite coating had the good electrochemical performance.
  • Effect of Solution Temperature on Corrosion Resistance of ZK60 Magnesium Alloy
    LI Qingfen, WU Yuanzhi, DENG Bin, LI Li, LIU Anmin
    Materials For Mechanical Engineering. 2017, 41(11): 29-32,38. https://doi.org/10.11973/jxgccl201711005
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    ZK60 magnesium alloy was solution-treated at different temperature (200-300℃). The microstructure was observed by scanning electron microscope (SEM) and corrosion resistance of the alloy in mass fraction of 3.5% NaCl solution was studied by the mass loss method and electrochemical method. The results indicate that the content of second phase in the alloy decreased with the increase of solution temperature, and the distribution of second phase changed from continuity into discontinuity. The corrosion rate increased first and then reduced with the increase of solution temperature. The optimal corrosion resistance was obtained at solution temperature of 300℃, and the corrosion rate, free corrosion current density and free corrosion potential were 4.575 2 mm·a-1, 0.011 639 mA·cm-2, -1.511 0 V, respectively.
  • Influence of Current Mode on Microstructure and Mechanical Properties of Nano-TiN/Ni Composite Coatings
    HE Jie, WU Menghua, LI Lintai
    Materials For Mechanical Engineering. 2017, 41(11): 33-38. https://doi.org/10.11973/jxgccl201711006
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    Nano TiN/Ni composite coatings were prepared on 45 steel substrate by the ultrasonic-electrodeposition method with a nickel sulfamate electroplating solution containing nano-TiN particles. The effects of the three current modes of direct current, single pulse and positive-negative pulse on surface morphology, nano-TiN content and distribution, interface binding force, microhardness and friction-wear performance of the coatings were compared and studied. The results show that compared to those by direct current electrodeposition, the grains of the pusle electrodeposited coating were finer, the surface was smoother, the surface cracks was fewer and the interface binding force was higher. The interface binding force of the positive-negative pulse electrodeposited coating was higher than that of single pulse electrodeposited coating. It was relatively easy for the pulse electrodeposition to deposite nano-TiN particles. The nano-TiN particle deposition rate by positive-negative pulse electrodeposition was higher than that by single pulse electrodeposition. The microhardness of the positive-negative pulse electrodeposited coating was the highest and its friction-wear performance was the best, while those of the direct current electrodeposition coating were the worst.
  • Fatigue Crack Propagation Rates in Different Zones of TA2 Titanium Alloy Welded Joint
    WEN Leilei, ZHOU Changyu, LI Jian, LU Lei
    Materials For Mechanical Engineering. 2017, 41(11): 39-44. https://doi.org/10.11973/jxgccl201711007
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    The fatigue crack propagation rate, fatigue fracture morphology and microstructure in base metal, fusion line, weld center and heat affected zone of TA2 titanium alloy welded joint were studied. The results show that the fatigue crack propagation rates in different zones of the joint had small difference and thus could be directly presented by the crack propagation rate of the weld zone. The fracture of samples from different zones illustrated typical fatigue fracture morphology. The average grain size of the base metal was about 62.8 μm, and that of the heat affected zone was about 110 μm. The grain size had little influence on the fatigue crack propagation rate.
  • Forming Reason and Resolving Measures of Island Defects on the Surface of Zirconium Alloy Plate
    XU Bin, GAO Feng, MA Qian, TONG Longgang, GONG Xiaotong
    Materials For Mechanical Engineering. 2017, 41(11): 45-47,52. https://doi.org/10.11973/jxgccl201711008
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    The reason of island defects on the the surface of zirconium alloy plate after pickling was analyzed by morphology observation of island defects, chemical composition analysis and surface treatment tests. The resolving measures was risen to avoid the island defects. The results show that the island defects were formed because the inclusion and oxide layer on the surface of plate resulted in the different pickling rates. The island defects could be avoided by adding the polishing before pickling to uniform the plate surface and using zirc-alloy with niobium to form NbF film during picking that could reduce the amount of island defects.
  • Effects of Mn Content on Microstructure and Properties of Biomedical Ti-29Nb-6Ta-5Zr Alloy
    SI Yi
    Materials For Mechanical Engineering. 2017, 41(11): 48-52. https://doi.org/10.11973/jxgccl201711009
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    Ti-29Nb-6Ta-5Zr-xMn(x=0,1,2,4,mass fraction/%) alloys were fabricated by nonconsumable electrode vacuum arc furnace and treated by solid solution. The effects of Mn content on the microstructure, mechanical properties and electrochemical corrosion resistance of the alloy were studied. The results show that the microstructures of all tested alloys were composed of a single β phase with equiaxed grains. The average grain size and lattice constant decreased with increasing content of Mn. The tensile strength, yield strength and hardness of the tested steel increased with increasing content of Mn and reached the largest values of 609 MPa, 585 MPa and 252 HV with 4wt% Mn, improved by 75.2%,70.1% and 58.4% comparing to those without Mn, respectively. The elongation and elastic modulus first decreased and then increased slightly with increasing content of Mn, however, the increase range was small. The corrosion potential of tested alloy containing 4wt% Mn was the highest, indicating the minimal tendency of corrosion.
  • Development of 38MnVS Non-quenched and Tempered Steel Automobile Semi-Axle
    SUN Hua, LI Shen, ZHOU Lei, MAO Xiangyang, ZHAO Xiuming
    Materials For Mechanical Engineering. 2017, 41(11): 53-58. https://doi.org/10.11973/jxgccl201711010
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    The 38MnVS non-quenched and tempered steel semi-axle was developed. The effect of cooling rate after hot forging on microstructure and mechanical properties of 38MnVS non-quenched and tempered steel semi-axle was studied and cpmpared with 42CrMo quenched and tempered semi-axle. The main factors affecting the fatigue life of the semi-axle were discussed. The results show that the size of ferrite and pearlite lamellar spacing of 38MnVS non-quenched and tempered steel reduced by force air cooling after hot forging, and the impact toughness increased from 16.8 J after air cooling to 43.7 J after force air cooling. 38MnVS non-quenched and tempered steel had good hardenability. The fatigue life of 38MnVS non-quenched and tempered steel semi-axle was equivalent to that of the 42CrMo quenched and tempered steel semi-axle, and the fatigue life of 38MnVS non-quenched and tempered steel semi-axle could reach more than 300 000 times by reducing the spline modulus, increasing spline root fillet radius and increasing the depth of the hardened layer appropriately that could replace 42CrMo quenched and tempered steel semi-axle.
  • Microstructure and Hardness Distribution of Electron BeamWelded Joint of 60 mm Thick Q345 Steel Plate
    DENG Zenghui, LI Dong, TONG Shaohui, FANG Hu
    Materials For Mechanical Engineering. 2017, 41(11): 59-62. https://doi.org/10.11973/jxgccl201711011
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    Q345 steel plates with thickness of 60 mm were joined by electron beam welding and the microstructure and microhardness distribution in the weld zone were studied. The results show that the 60 mm thick Q345 steel plates were welded with full penetration by the single pass electron beam welding. The welded joints in good shapes and without obvious defects such as pores and cracks were obtained. The weld depth-to-width ratio was as high as 15:1. The microstructure at the top of weld zone consisted of proeutectoid ferrite, side-plate ferrite and acicular ferrite. Along the depth of the weld, the amount of ferrite decreased while that of the lath martensite and acicular ferrite increased, the spacing between acicular ferrites became smaller and the grain size was reduced. From top layer to root layer of the weld, the hardness in the weld center showed a fluctuant increasing trend. The microhardness of the weld zone was higher than that of base material and heat affected zone. The increasing rate of the hardness in the weld zone increased obviously along the depth.
  • Properties of Al2O3/ZrO2 Composite Structural Thermal Barrier Coating Prepared by Plasma Spraying Method
    YANG Hongbo, LIU Zhaohui, YI Tongbin, LIU Na, SHU Xin, LUO Ping
    Materials For Mechanical Engineering. 2017, 41(11): 63-67,72. https://doi.org/10.11973/jxgccl201711012
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    Three kinds of thermal barrier coating were prepared on the surface of 304 stainless steel by plasma spraying method with NiCrAlY served as metal bonding layer material and Al2O3 and ZrO2 served as the ceramic layer materials. The microscopic morphology and crystalline phase of the coating was characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The high temperature oxidation resistance and thermal shock resistance of the coating were also studied. The results show that NiCrAlY/Al2O3/ZrO2 composite structural thermal barrier coating surface did not have any hole and crack, and there were Mg2Zr5O12 and (Fe, Mg) (Cr, Fe)2O4 crystalline phase in the coating after high temperature oxidation. NiCrAlY/ZrO2 coating had the best high temperature oxidation resistance because of the oxygen barrier effect of Al2O3. The thermal expansion coefficient of interlayer material in NiCrAlY/ZrO2 coating had a gradient trend and the coating exhibited the best thermal shock resistance.
  • Effect of Rare Earth Element La on Microstructure and Mechanical Properties of A356 Aluminum Alloy for Automobile Wheel Hub
    XU Heng
    Materials For Mechanical Engineering. 2017, 41(11): 68-72. https://doi.org/10.11973/jxgccl201711013
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    The effect of rare earth element La on microstructure and mechanical properties of A356 aluminum alloys for automobile wheel hub was investigated by optical microscope, scanning electron microscope and tensile testing machine. The results show that the primary phase α-Al in the A356 aluminum alloy was refined after rare earth element La added. The morphology of eutectic Si changed from coarse acicular or lath-like into tiny fibrous. The mean area and aspect ratio of eutectic Si reduced from 126 μm2 and 18.2 to 7.8 μm2 and 1.8, respectively. AlSiLa intermetallic compound was obtained in the A356 aluminum alloy after rare earth element La added. The tensile strength and elongation increased first and then decreased with the increase of content of rare earth element La in the aluminum alloy. When the mass fraction of rare earth element La was 0.6%, the aluminum alloy had the maximum tensile strength and elongation which were 215 MPa, 5.4%, respectively.
  • Effect of Friction Pressure on Mechanical Properties of Friction Welding Joint of 2A12 Aluminum Alloy
    YANG Feng, ZHANG Dekun, SHI Duanhu, XIA Xiaolei, LU Xinghua
    Materials For Mechanical Engineering. 2017, 41(11): 73-76,81. https://doi.org/10.11973/jxgccl201711014
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    2A12 aluminium alloy was welded by the friction welding under different friction pressure. The microstructure of welding zone was analyzed by optical microscopy and electron backscattered diffraction technique. The influence of the friction pressure on the mechanical properties of the joints was discussed. The results show that the dynamic recrystallization occurred in the welding zone, grains were refined and predominantly bounded by high angle boundaries. The tensile strength of joint increased first and then decreased with the increase of friction pressure. When the friction pressure was 60 MPa, the tensile strength was maximum and the value was 412 MPa. The distribution of microhardness all showed "W" type under different friction pressure, and soften behavior appeared in heat affected zone because of the transformation and coarsening of the strengthening phase S'.
  • Microstructure and Tensile Properties of 6061 Aluminum Alloy/Q235 Galvanized Steel Brazing Welded Joint Prepared by Cold Metal Transfer
    WANG Yan, YANG Shanglei, ZOU Yuguo, JIANG Yishuai, YANG Zhihua
    Materials For Mechanical Engineering. 2017, 41(11): 77-81. https://doi.org/10.11973/jxgccl201711015
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    6061 aluminum alloy and Q235 galvanized steel were butt welded by cold metal transition(CMT) brazing. The microstructure and tensile properties of welded joints were studied. The results show that the welded joint surface was well formed. The welded joint was composed of fusion zone, heat-affected zone and interface layer. The fusion zone consisted of α-Al solid solution and aluminum-silicon eutectic structure. The microstructure of heat-affected zone was coarser than that of the parent metal. Intermetallic compound (IMCs) was formed in the interface layer, the layer thickness was about 8 μm, and the layer grew unidirectionally to the melting zone. The hardness of the heat-affected zone on the side of 6061 aluminum alloy base metal was the lowest (42 HV), and the hardness of the IMCs layer was the highest (365 HV). The tensile strength of the welded joint was 161 MPa, which was about 0.69 times as that of 6061 aluminum alloy, and was improved obviously compared with lap joints.
  • Finite Element Simulation for Welding Deformation and Residual Stress in Pressure Wheel of Road Roller
    FANG Yuanbin, WANG Yong, WANG Can, LU Yongneng
    Materials For Mechanical Engineering. 2017, 41(11): 82-85,90. https://doi.org/10.11973/jxgccl201711016
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    On the basis of thermo elastic plastic theory and finite element analysis method, the finite element model of the press wheel was established and the welding deformation and residual stress distributions of the pressure wheel were simulated. The residual stresses of the pressure wheel were measured by a blind-hole method and compared with those by simulation. The results show that two sealing plates had a convex shape due to the welding deformation. The maximum deformation amount was 5.732 mm. The residual stresses at the welding arc and weld seam of the pressure wheel after welding were relatively large. The peak value of stresses was 416.40 MPa. With increasing distance from the free edge of circular plate, the residual stress at the straight weld center of the circular plate first increased then decreased and then increased. The measured residual stresses coincided well with those from the simulation, indicating the accuracy of the simulation.
  • Deformation Behavior and Constitutive Equation Establishment of Low Carbon Steel at High Temperature
    WANG Lei, GU Lizhi
    Materials For Mechanical Engineering. 2017, 41(11): 86-90. https://doi.org/10.11973/jxgccl201711017
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    Deformation behavior of QD08 low carbon steel at high temperature was investigated by thermal simulator with strain rates of 0.1-10 s-1 at 1 000-1 200℃. The true stress-true strain curves of the low carbon steel at high temperature were obtained, the dynamic recrystallization behavior of QD08 low carbon steel was analyzed, and the constitutive equation of hot deformation was established based on the Arrhenius function with hyperbolic sine form. The results show that the peak stress increased with the decrease of deformation temperature or the increase of strain rate during deformation at high temperature. The predicted value of the peak stress calculated by the constitutive equation was in good agreement with the experimental results. The established constitutive equation could represent high temperature deformation behavior of QD08 low carbon steel.
  • Static Softening Behavior of Low Carbon High Niobium X100 Pipeline Steel
    XIA Dianxiu, NIU Yanlong, DU Hengke
    Materials For Mechanical Engineering. 2017, 41(11): 91-95,101. https://doi.org/10.11973/jxgccl201711018
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    The static softening behavior of low carbon high niobium X100 pipeline steel was studied by double pass hot compression test carried on thermal simulator. The static recrystallization kinetics model of the low carbon high niobium high strength pipeline steel was established. The results show that the static softening behavior of the tested steel was distinctly affected by deformation temperature and interval time. With the increase of deformation temperature and prolongation of the interval time, the static softening rate of the tested steel increased. When the deformation temperature was below 950℃, static recrystallization behavior did not occur.When the deformation temperature was higher than 1 000℃, the tested steel achieved complete static recrystallization. The activation energy of static recrystallization of the steel was 325 kJ·mol-1 which calculated by the kinetics model. And the result was consistent with that calculated by the empirical formula based on the chemical composition.
  • Numerical Simulation of Forming Limit of Hot Rolled Pickling Sheet Based on Maximum Second-order Principal Strain and Savitzky-Golay Smoothing Principle
    CHEN Yanxing, CHEN Jianjun, YUAN Weijie
    Materials For Mechanical Engineering. 2017, 41(11): 96-101. https://doi.org/10.11973/jxgccl201711019
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    Finite element software ABAQUS was used to simulate the hemispherical punch stretching tests of hot rolled pickling sheet. The location of global necking in the forming process of pickling sheet was analyzed. The first-order and second-order derivative of the principal strain were fitted by the Savitzky-Golay smoothing principle to obtain the curve of second-order principal strain with time. The forming strain limit of hot rolled pickling sheet was predicted based on the maximum second-order principal strain criterion, and compared with the experimental results. The results show that the forming limit based on finite element simulation and data fitting was slightly lower than the experimental results. The maximum error of the principal strains was 2.2%. The simulation results were in good agreement with the experimental results, which could be used to predict the forming limit of hot rolled pickling sheet.
  • Failure Analysis of 20Cr32NiNb Steel Hot Outlet Manifold
    NI Yingying, TANG Jianqun, GUO Xiaofeng, GONG Jianming
    Materials For Mechanical Engineering. 2017, 41(11): 102-105,110. https://doi.org/10.11973/jxgccl201711020
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    The hot outlet manifold of CO reformer used in a factory cracked prematurely after its service for 2 a. The failure analysis of the cracked outlet manifold was performed by macroscopic observation of the fracture, scanning electron microscope observation, chemical composition analysis and mechanical property tests. The results show that the failure type of the outlet manifold was creep cracking. Because the outlet manifold served at high temperature for a long time, creep cavities generated along grain boundaries and grew gradually at high temperature and stress. The adjacent cavities connected or merged together to form cracks. Cracks propagated gradually and finally the outlet manifold cracked under the stress.
  • Cracking Reason of Inconel 800 Alloy Bellows
    PAN Hengpei, XIA Shenlin, YANG Xiao
    Materials For Mechanical Engineering. 2017, 41(11): 106-110. https://doi.org/10.11973/jxgccl201711021
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    The cracks were found on the Inconel 800 alloy bellows in a petrochemical company after temporary stoppage. The cracking reason was analyzed by chemical composition analysis, macroscopic and microscopic morphology observation, scanning electron microscopy and energy spectrum analysis, transmission electron microscope analysis. The results show that the sensitization of bellows occurred during application and were in the polythionic acid environment during the stoppage time which resulted in the intergranular corrosion. The microcracks produced by intergranular corrosion were the source of cracks and eventually the microcracks extended and resulted in the formation of stress corrosion cracks under the action of stress.
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