10 January 2022, Volume 45 Issue 12
    

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  • Research Status of Pulse Current Treatment and Assisted Metal Manufacturing Technology
    SUN Fujian, WAN Shang, XIAO Gang, LI Shichun, LIU Yiliang, WAN Keqian
    Materials For Mechanical Engineering. 2021, 45(12): 1-6. https://doi.org/10.11973/jxgccl202112001
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    When pulse currents are applied to metal materials, thermal and non-thermal effects will occur.The coupling of the two effects can promote dislocation movement and atom diffusion and increase the mobility of vacancy diffusion, leading to the evolution of microstructure of metal materials and forming an electroplastic effect.On the basis of the basic theory of electroplastic effects, the research progress on the pulse current treatment regulating the microstructure of metal materials and the application of pulse currents in auxiliary plastic processing and cutting processing are reviewed.It is pointed out that future researches are focused on the coupling mechanism of thermal effects and non-thermal effects in pulse current treatment and pulse current assisted processing, and current density distribution in application to complex structure parts, etc.
  • Welding Cold Crack Sensitivity of Q690ZM Medium-Mn Steel
    QI Xiangyu, YAN Ling, ZHANG Peng, WANG Xiaohang, DU Linxiu
    Materials For Mechanical Engineering. 2021, 45(12): 7-12,18. https://doi.org/10.11973/jxgccl202112002
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    The sensitivity of welding cold crack of medium-Mn steel was investigated by a maximum hardness test and Y-groove welding cracking test through Ar-CO2 gas shielded welding.The results show that when the welding heat input increased from 10 kJ·cm-1 to 20 kJ·cm-1 or the preheating temperature increased from 20 ℃ to 200 ℃, the microhardness of the welding heat affected zone of medium-Mn steel decreased slightly, and the maximum hardness was higher than 430 HV, indicating the steel had a severe welding cold cracking tendency.The surface crack and root crack of test weld in Y-groove welding cracking test disappeared and the section crack rate decreased to 9.09%, when the welding heat input was 15 kJ·cm-1 and the preheating temperature increased from 100 ℃ to 200 ℃.In order to prevent welding cold crack formation, the preheating at 150-200 ℃ before welding medium-Mn steel and post-weld heat treatment should be carried out.The large martensitic lath in coarse-grained heat affected zone had little difference in crystallographic orientation and had a low density of large angle grain boundaries, which had weak resistance to cleavage crack propagation; thus, the welding cold crack extended along the coarse-grained heat affected zone adjacent the fusion line after initiation.
  • Effect of Hydrogen on Surface Morphology and Mechanical Properties of As-cast Mg-14Li Alloy
    LIU Li, XU Daokui, MU Yongliang, WANG Shuo, XU Xiangbo
    Materials For Mechanical Engineering. 2021, 45(12): 13-18. https://doi.org/10.11973/jxgccl202112003
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    Cathodic hydrogen charging was conducted on the as-cast Mg-14Li alloy with hydrogen charging times of 0-18 h.The surface morphology and tensile properties of the alloy before and after hydrogen charging were compared and analyzed.The results show that pitting corrosion occurred on the surface of as-cast Mg-14Li alloy after cathodic hydrogen charging, and the LiCO3 corrosion product film was destroyed.The depth of corrosion pits and the quantity of corrosion products increased with the hydrogen charging time.However, no microcracks were found in the alloy after hydrogen charging, indicating that the hydrogen embrittlement sensitivity of β-Li phase was low.With the increase of hydrogen charging time, the yield strength, tensile strength and percentage elongation after fracture of as-cast Mg-14Li alloy decreased, and the dimples on the fracture surface decreased and the cleavage surface increased in amount, indicating that the fracture mode of as-cast Mg-14Li alloy changed from ductile fracture to brittle fracture.
  • Influence of Rolling Reduction on Interfacial Bonding Performance of Carbon Steel/Stainless Steel Clad Plate
    LI Tianmei, DING Wenhong, MING Yafei, WU Mengxian, YANG Yun
    Materials For Mechanical Engineering. 2021, 45(12): 19-25. https://doi.org/10.11973/jxgccl202112004
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    Q235 carbon steel/304 stainless steel clad plate was fabricated by non-vacuum rolling asymmetric billet with different total reductions (28%-70%).The microstructure, inclusion morphology, hardness and shear strength at interfaces of the clad plate were studied, and the competitive effects of inclusion and decarburization layer on the interface bonding strength were discussed.The results show that with increasing total rolling reduction, the inclusions at the interface of the clad plate changed from concentrated lump to uniform granular.When the total rolling reduction increased from 28% to 47%, the interface inclusion was the main factor affecting the bonding strength; increasing the rolling reduction was beneficial to improve the interface bonding strength.When the rolling reduction increased from 47% to 70%, the grain size on stainless steel sides decreased sharply, the thickness of decarburization layer at carbon steel side increased, and the interface bonding strength decreased; the decarburization layer become the dominant factor affecting the bonding strength.The competitive effects of interface inclusions and decarburization layers on bonding strength could be balanced by controlling the rolling reduction reasonably.
  • Effect of Graded Transition Layer on Tensile Strength and Ductility of Parallel Structures of Heterogeneous Resin Materials
    YANG Quanquan, CAO He, LI Yun, TANG Youcheng, ZHU Shuai
    Materials For Mechanical Engineering. 2021, 45(12): 26-30,41. https://doi.org/10.11973/jxgccl202112005
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    Seven resin materials with decreasing elastic moduli were selected.Tensile specimens with four interface structures were prepared by multi-material jet printing of two materials with the smallest and the largest elastic moduli; the two materials were connected parallelly.The interface structures were listed as follows:without transition layer, with homogeneous transition layer (composed of one material with mediate elastic modulus), and with 3 mm and 5 mm thick graded transition layers (composed of other five materials).The interface forming quality and tensile properties were analyzed.The results show the specimen without transition layer had grooves and much holes at interfaces, indicating a poor forming quality.With a homogeneous transition layer, the defects at the interface decreased in amounts, the tensile strength increased slightly, but the fracture strain decreased by 14.8%.With graded transition layers, the interface forming quality further increased, the tensile strength increased slightly and the ductility increased obviously.Comparing with that without transition layers, the fracture strains of specimens with 3 mm and 5 mm thick graded transition layers increased by 10.6%, 37.9%, respectively.
  • Effects of Welding Speed on Microstructure and Properties of 304 Stainless Steel Electron Beam Welded Joint
    YANG Tao, YUAN Mengyang, JIAN Hailin, LI Dong
    Materials For Mechanical Engineering. 2021, 45(12): 31-35. https://doi.org/10.11973/jxgccl202112006
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    304 stainless steel plates with thickness of 3 mm were welded by vacuum electron beam welding under accelerating voltage of 120 kV, focus current of 2 460 mA, and welding current of 12 mA.The effects of welding speed (10-40 mm·s-1)on microstructure and mechanical properties of the joints were studied.The results show that microstructures of the weld mainly consisted of columnar grains at both sides and equiaxed grains in center.With increasing welding speed, the grains size of the weld decreased, the volume fraction of ferrite increased, the hardness of all areas in joints increased, the tensile strength increased first and then decreased, and the fracture of joints all occurred at base metal after tension.Under the experimental conditions, the optimal welding speed for 304 stainless steel by the vacuum electron beam welding was 30 mm·s-1; at this time the welded joint had good forming quality with ferrite volume fraction of 7.4%, relatively high hardness, and the largest tensile strength of 640 MPa; the tensile fracture showed the characteristics of ductile fracture.
  • Influence of Lubrication Condition and Cylinder Liner Material on Friction and Wear Characteristics of Piston Ring-Cylinder Liner
    QU Lei, JIANG An, WANG Zhong, XIE Weian
    Materials For Mechanical Engineering. 2021, 45(12): 36-41. https://doi.org/10.11973/jxgccl202112007
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    Friction and wear tests were conducted on YH31 alloy cast iron piston ring and cylinder liner of different materials (high boron copper cast iron and CrMoAl cast iron)under lubrication conditions of lubricating oil without and adding 0.1wt% MoS2.Influence of the lubrication condition and cylinder liner material on the friction coefficient, volumetric wear loss and wear surface morphology was studied, and the wear mechanism was analyzed.The results show that adding MoS2 shortened the running in period of the piston ring and high boron copper cast iron cylinder liner, prolonged the stable wear period, decreased the friction coefficient and reduced the volumetric wear loss; the wear marks on the rubbing pair surfaces were finer and more shallow than those under the lubrication condition without MoS2, and no cracks were found.Under the lubrication condition without MoS2, the piston ring matched with CrMoAl cast iron cylinder liner entered the stable wear stage earlier than that matched high boron copper cast iron cylinder liner, but the stable wear stage lasted shortly, the average friction coefficient increased, and the volumetric wear loss increased greatly.The wear mechanism of the piston ring was polishing wear; the high boron copper cast iron and CrMoAl cast iron cylinder liner had abrasive wear+fatigue wear and abrasive wear mechanisms, respectively.
  • Remelting and Wire Cladding Process by TIG Cold Welding on Surface of 1Cr17 Stainless Steel and Microstructures and Properties of Modified Layers
    ZHENG Shaoxian, WANG Junping, YANG Meijuan, E Xin
    Materials For Mechanical Engineering. 2021, 45(12): 42-48. https://doi.org/10.11973/jxgccl202112008
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    Process tests for remelting and cladding of ER347L stainless steel wires by tungsten inert gas arc (TIG)cold welding were carried out on surface of 1Cr17 stainless steel.The microstructure, microhardness and electrochemical corrosion property in 3.5wt% NaCl solution of the remelting layer and cladding layer were studied.The results show that for the TIG cold welding remelting, when the cold welding time was in the range of 200-150 ms, 150-100 ms, 100-50 ms, the required minimum cold welding current for obtaining well-formed remelting layer was 40, 70, 100 A, respectively.For the TIG cold welding cladding, when the cold welding time was 50, 100, 160, 200 ms, the required minimum cold welding current for obtaining well-formed cladding layer was 230, 190, 150, 120 A, respectively.The grains of heat affected zone (HAZ)formed in TIG cold welding remelting or cladding were not coarsened comparing with those of 1Cr17 stainless steel base metal, and the HAZ width did not exceed 250 μm.The microstructures of the remelting layer and cladding layer were finer than that of the base metal.The microhardness and corrosion resistance of the remelting layer and cladding layer were higher than those of the base metal.
  • Properties of Microalloying Low-Silver and Cadmium-Free Ag-Cu-Zn Brazing Filler Metal
    WANG Xiaofei, JIN Chengkai, FANG Yunqi, LI Jing, PENG Yutao, WANG Xiaorong, SHEN Hangyan, LIU Wei
    Materials For Mechanical Engineering. 2021, 45(12): 49-54. https://doi.org/10.11973/jxgccl202112009
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    The Ag-Cu-Zn brazing filler metal containing 21wt% Ag was microalloyed with Sn, P, Ni and In, and the melting performance, spreading performance and processing property for brazing filler metal, and the tensile strength and microstructure of the brazed red copper and 45 steel joint were studied.The results show that the optimum composition (mass fraction/%)of microalloyed Ag-Cu-Zn brazing filler metal was 21Ag-Cu-Zn-1.5Sn-0.2P-1.0Ni-2.5In.Compared with 21Ag-Cu-Zn-1.5Sn quaternary alloy brazing filler metal obtained by prior optimization, the solidus and liquidus temperatures decreased by 106 ℃ and 31 ℃, respectively, the spreading area per mass on red copper base metal increased by nearly 66%, and welding wire with diameter of 0.8 mm could be made by conventional hot extrusion and drawing.When the brazing filter metal was used for brazing red copper or 45 steel, a dense and defect-free brazing joint formed with a metallurgical bonding layer at the interface; compared with 21Ag-Cu-Zn-1.5Sn brazing filler metal, the tensile strength of the joint for brazing 45 steel increased by about 11%.
  • Interface Microstructure and Tensile Properties of Different-Bevel-Angle Galvanized Steel/Aluminum Alloy Joint by Laser Fusion Brazing
    YANG Yang, ZHOU Xin, YU Shuang, BAI Yujie, Lü Yanan
    Materials For Mechanical Engineering. 2021, 45(12): 55-61. https://doi.org/10.11973/jxgccl202112010
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    6061-T6 aluminum alloy plate and AISI 1045 galvanized steel plate were welded by laser fusion brazing with ER4043 welding wires; the bevel angle of the aluminum alloy plate was 30°, and that of the steel was 30° and 60°, respectively.The microstructure and micro-zone composition of the brazing interface on the steel side were studied, and the tensile properties of the joint were tested.The results show that zinc-rich areas and microvoids were formed at weld toe and weld root on the brazing interface of the joint when the bevel angle of steel plate was 60°, and a continuous intermetallic compound layer was formed at other areas on the interface.For the joint wth the steel plate bevel angle of 30°, zinc-rich areas were only formed at the weld toe, and a continuous intermetallic compound layer was formed at the entire brazing interface.In the two joints, the thickness of the intermetallic compound layer on the lower area of the steel plate groove surface was higher.The thickness of the intermetallic compound layer in the joint with the steel plate bevel angle of 30° was greater than that with the steel plate bevel angle of 60°.The average tensile strength of joints with the steel bevel angles of 30° and 60° was 120.3, 151.7 MPa, respectively.The two joints fractured at the steel/weld interface during tension, and both fractured in cleavage fracture form.
  • Engineering Estimation Method of Creep Fracture Parameter C for Axial Internal Surface Cracked Pipes under Internal Pressure
    LIU Changjun, CAI Jun, SUN Chunyan, TAN Jianping, SHAO Xuejiao
    Materials For Mechanical Engineering. 2021, 45(12): 62-66. https://doi.org/10.11973/jxgccl202112011
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    With axial internal surface cracked pipes under internal pressures as the research object, the creep fracture parameter C* estimation method proposed by Zahoor was improved by introducing the x0 parameter to make the J-integral full plastic solution independent of Norton indexes.The C* values under the conditions of different Norton indexes and different crack size were calculated by the improved method, Zahoor solution, and reference stress methods including R6 global solution and Kim solution, and were compared with the finite element calculation.The results show that the C* values calculated by the reference stress methods were two to eight times higher than those by the finite element calculation; the accuracy of the reference stress methods was poor.The ratios of the C* values calculated by the improved method to the finite element calculation results were close to 1; the accuracy of the improved method was relatively high.Comparing with the Zahoor solution, the improved method had higher calculation accuracy with the Norton index of 3.But as the Norton index increased, the calculation accuracy of the two methods tended to be the same.
  • Occupation of Hydrogen Atom in Intermetallic Compound θ-Al2Cu:A First-Principles Calculation
    SONG Lili, FU Gaosheng, LI Longze, WANG Huosheng
    Materials For Mechanical Engineering. 2021, 45(12): 67-71,77. https://doi.org/10.11973/jxgccl202112012
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    When hydrogen atoms dissolved into θ-Al2Cu unit cell, they could occupy octahedral interstitial site or tetrahedral interstitial sites.Influence of hydrogen dissolution on the θ-Al2Cu unit cell structure, system total energy, formation energy, and Mulliken bond population and bond length between neighboring atoms in interstitial structures was analyzed by first-principles method.The tendency of hydrogen atoms occupying positions in θ-Al2Cu was analyzed.The results show that when the hydrogen atom occupied the octahedral interstitial site, the system energy was the lowest, the formation energy was the smallest and negative, and the lattice distortion was the smallest; the bond population was positive and the bond lengths were the shortest between neighboring atoms, and the bond cooperation was the strongest.Therefore, when hydrogen atoms occupied θ-Al2Cu octahedral interstitial site, the structure was more stable.
  • Effect of Heat Input on Microstructure and Toughness of Welding Coarse-Grained Heat Affected Zone of 09MnNiDR Steel
    LI Jinmei, YANG Zhaoqing, LIANG Xiaowu, ZHANG Jianxiao, LEI Wanqing, CAO Rui
    Materials For Mechanical Engineering. 2021, 45(12): 72-77. https://doi.org/10.11973/jxgccl202112013
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    Thermal simulation tests were conducted on 09MnNiDR steel to prepare welding coarse-grained heat affected zone (CGHAZ)samples at different heat inputs by using a Gleeble-3800 thermal simulator.The effect of the heat input on microstructures, hardnesses and impact toughness of the samples was studied.The resutls show that with increasing heat input, the microstructure of the CGHAZ sample changed from lath bainite+granular bainite to granular bainite+massive ferrite, and the hardness decreased.The maximum impact absorbed energy at -70 ℃ of CGHAZ samples at different heat inputs was only 31 J, which did not meet the requirements; the granular bainite structure was the main reason for the deterioration of toughness.With increasing heat input, the grain size of prior austenite in CGHAZ samples decreased and then increased.Therefore, the impact absorbed energy at -70 ℃ of the samples increased and then decreased.
  • Numerical Simulation and Experimental Verification of Fatigue Life of Q420D High-Strength Steel Transverse-Cruciform Weld Joint
    CHENG Haigen, HU Cong, JIANG Yong
    Materials For Mechanical Engineering. 2021, 45(12): 78-83,89. https://doi.org/10.11973/jxgccl202112014
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    The fitting stress amplitude-fatigue life (S-N)curve of Q420D high-strength steel transverse-cruciform weld joint was obtained by fatigue tests (test fitting).The fatigue lives of the cruciform joint were predicted by the co-simulation of ANSYS and FE-SAFE softwares, and then the S-N curve was obtained by fitting (numerical fitting).The results by test fitting and numerical fitting were analyzed in contrast.The effects of current code evaluating the fatigue life of the cruciform joint were analyzed.The results show that the relative errors between the numerical fitted and the test fitted fatigue lives of the cruciform joint were not higher than 3.49%, and the relative error of the fatigue limit was 0.93%, indicating the application of ANSYS and FE-SAFE software co-simulation technique to predicting the fatigue life of the cruciform joint was reliable.The test fitted S-N curve (50% survival probability)was in good agreement with the ANSI code designed curve, while the test fitted curve at 95% survival probability was in good agreement with the DNV code designed curve.When the number of cycles was higher than 2×105 cycles, the EN code could better evaluate the fatigue life of the cruciform weld joint than the ANSI code, and had sufficient safety margins.
  • Effect of Heat Input on Welding Thermal Cycle and Residual Stress of V-joints at Different Positions of Motor Bracket
    LI Gang, GUAN Meng, ZHANG Yanmin, FAN Lingli, LI Lianhai, LIN Bin, YANG Kang
    Materials For Mechanical Engineering. 2021, 45(12): 84-89. https://doi.org/10.11973/jxgccl202112015
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    A tubular motor bracket model with six V-joints was established with a nonlinear finite element software Marc.The influence of heat input on the thermal cycle at the arcing end and the residual stress in welds of six V-joints were simulated and studied.The results show that the higher the heat input, the higher the peak temperature at the arcing end, and the more uniform the heat of the joint during heating and cooling processes.The heat input had a small effect on the welding residual stress at the front and end of the welds.For the middle of the welds, the greater the heat input, the smaller the welding residual stress; except for the joint II, the residual stresses in the middle of welds of other joints were all tensile stresses.
  • Reason for Explosion of Buffer Tank of a Liquefied Natural Gas Bus
    HUANG Huandong, SHEN Zhengxiang, CHEN Wenfei, ZHANG Hanlin, CHEN Hu
    Materials For Mechanical Engineering. 2021, 45(12): 90-92,102. https://doi.org/10.11973/jxgccl202112016
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    After breakdown of a liquefied natural gas bus, the cut-off valve of the gas cylinder was closed.And then the gas supply system experienced pipeline freezing and natural gas leakage.The buffer tank in the gas supply system exploded when the pipeline was deiced with normal temperature natural water.The explosion reason for the buffer tank was analyzed by chemical composition test, microstructure and fracture morphology observation, and stress checking.The results show that the liquefied natural gas experienced rapid phase transition during the deicing with normal temperature water, leading to sharply increased pressure in the system.When the pressure exceeded the explosion pressure of the buffer tank, the buffer tank exploded.It was suggested to install a secondary safety valve on the top of the buffer tank, and to set a vent pipe for the safety valve.The risk of explosion of the buffer tank could be effectively reduced by venting the pressure through the vent pipe.
  • Fracture Cause of High-Speed Carburized Gear Tooth in a Thermal Power Plant
    PENG Bo, ZHANG Bin, ZHANG Chuanzheng, SONG Zibo, HAN Zhewen, LI Ling, WANG Zhichun
    Materials For Mechanical Engineering. 2021, 45(12): 93-98. https://doi.org/10.11973/jxgccl202112017
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    Several gear teeth of a secondary driven carburized gear for a feed water pump coupler in a thermal power plant were broken.The fracture cause of gear teeth was analyzed by macro and micro morphology observation, chemical composition measuring, metallographic inspection and mechanical property testing.The results show that the surface hardness of the carburized layer of the gear tooth flank was insufficient, and the wear resistance and fatigue resistance were poor.The surface metal of the gear tooth flank peeled off to form spalling pits under long-term repeated contact stresses.Meanwhile flake defects existed in the microstructure of the gear.The comprehensive mechanical properties of the material were inadequate.During the high-speed rotation of the gear, the tooth flank was subjected to contact stresses, and cracks were initiated at stress concentration areas around the spalling pits and expanded rapidly, resulting in the brittle fracture of the gear teeth.
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