20 October 2019, Volume 43 Issue 10

    

• Select all
  |

• Select
  Research Progress on Flux-Cored Brazing Filler Metals

  DONG Bowen, LONG Weimin, ZHONG Sujuan, DONG Xian, Lü Dengfeng

  Materials For Mechanical Engineering. 2019, 43(10): 1-5,65. https://doi.org/10.11973/jxgccl201910001

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The research progress on preparation technology, morphology, modification and application of three kinds of commonly used flux-cored brazing filler metals including flux-cored aluminum brazing filler metals, flux-cored silver brazing filler metals and flux-cored copper brazing filler metals is briefly described. The shortcomings of current research are pointed out. The research direction on the flux-cored brazing filler metals in the future will mainly focus on the following aspects:research on numerical simulation technology based on flux-cored brazing filler metal forming; research on the synergistic reaction between brazing alloy and brazing flux, and seam filling mechanism; research on low-cost and non-corrosive brazing flux; research and development of low-silver and low-cost flux-cored silver filler metals.
• Select
  Corrosion Resistance of Superhydrophobic Structure on Magnesium Alloy Surface Prepared by Hydrochloric Acid-Laser Composite Etching and SA Modification

  XU Leiqiu, WAN Xiaofeng, DONG Jing, SONG Debao, WEI Kequan, LIANG Zhipeng

  Materials For Mechanical Engineering. 2019, 43(10): 6-10,58. https://doi.org/10.11973/jxgccl201910002

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  A superhydrophobic structure was prepared on the surface of as-polished AZ91 magnesium alloy by hydrochloric acid-laser composite etching and stearic acid (SA) modification. The surface morphology, wetting properties and corrosion resistance of the superhydrophobic structure were studied. The results show that a rough structure composed of micron-sized pits and tightly and orderly arranged convex was formed on the magnesium alloy surface after the composite etching; after subsequent SA modification, a micro-nano-scaled composite rough structure was formed. After the composite etching and SA modification, the surface exhibited superhydrophobicity with good water-repellent adhesion resistance. Compared with those of the as-polished magnesium alloy, the free corrosion potential of the superhydrophobic magnesium alloy obtained by the composite etching and SA modification increased, and the free corrosion current density decreased, showing good corrosion resistance. After soaking in 3.5wt% NaCl solution for 24 h, the superhydrophobic surface showed no obvious corrosion traces.
• Select
  Effects of CO₂ and H₂S on Electrochemical Corrosion Behavior of FV520B Stainless Steel in NaCl Solution

  LUO Sheji, ZHAO Qing, RAN Zhaohui, YIN Shuzheng, WANG Qingguo, LIU Jun, CHEN Yang

  Materials For Mechanical Engineering. 2019, 43(10): 11-14. https://doi.org/10.11973/jxgccl201910003

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Electrochemical corrosion behavior of FV520B stainless steel in 3.5wt% NaCl solution and in 3.5wt% NaCl solutions containing CO₂, H₂S and CO₂+H₂S, respectively, was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the open circuit potential of the test steel shifted to the negative direction, the polarization resistance decreased and the corrosion resistance became worse. The polarization curves of the test steel in four corrosive media showed anodic dissolution characteristics. In the 3.5wt%NaCl and 3.5wt%NaCl+CO₂ solutions, the corrosion was dominated by anodic reaction; in the 3.5wt%NaCl+H₂S solution, the corrosion was dominated by cathodic reaction; the corrosion was dominated by the anodic and cathodic reaction when H₂S and CO₂ coexisted in the 3.5wt%NaCl solution.
• Select
  Corrosion Behavior of Q235 Steel in Three Typical Soil Environments

  ZHU Yichen, LIU Guangming, LIU Xin, PEI Feng, TIAN Xu, GAN Hongyu

  Materials For Mechanical Engineering. 2019, 43(10): 15-19. https://doi.org/10.11973/jxgccl201910004

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  The near-neutral yellow brown soil from Wuhan, the alkaline saline-alkali soil from Tianjin and the acid red soil from Nanchang were selected as corrosive media. The indoor simulated accelerated corrosion test of Q235 steel was carried out. The corrosion rate, corrosion morphology and corrosion product composition of the test steel were compared, and the corrosion mechanism was analyzed. The results show that the test steel in all the three soils had uneven comprehensive corrosion and local pitting. The outer layer structure of the corrosion products was loose, mainly composed of Fe₂O₃ and FeOOH. The inner layer structure was dense and mainly composed of Fe₃O₄. In the alkaline saline-alkali soil, a structurally complete corrosion product layer was formed on the surface of the test steel, which inhibited the oxygen-consuming reaction of the cathode; the corrosion rate was the lowest. The higher concentration of H⁺ in acid red soil promoted the process of the cathodic hydrogen evolution reaction and the generation of cracks; the corrosion rate of the test steel was the highest. In the later stage of corrosion, the dense inner rust layer of Fe₃O₄ was formed on the surface of the test steel; the corrosion rate of the test steel during 15 d was higher than that during 30 d.
• Select
  Microstructure and Hardness of Pressure Boundary Welded Joint of Nuclear Reactor Steam Generator

  SHI Yu, ZHANG Yingying, GUO Xiaoxiao, JI Qiang

  Materials For Mechanical Engineering. 2019, 43(10): 20-23,70. https://doi.org/10.11973/jxgccl201910005

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  According to the structure characteristics between the partition and positioning plates of the pressure boundary water chamber of nuclear reactor steam generator, the butt welding was conducted on Inconel600 alloy with an asymmetric X-groove design, and the microstructure and hardness of the welded joint were analyzed. The results show that the grain size in the heat affected zone of the welded joint was larger than that in the base metal. The structure of the fusion zone transitted well. The structure at the edge of the weld seam was composed of columnar crystal, growing perpendicularly to the fusion line toward the center of the weld seam, and the structure of the center of the weld seam was composed of columnar crystal and equiaxed crystal. More equiaxed crystals were formed in the remelting zone between the front and back sides of the weld seam. The phase composition of the weld seam consisted of γ phase, γ' interstitial phase and carbides, the same as that of the base metal. The hardness in the weld remelting zone was the highest while that of the heat affected zone was the smallest.
• Select
  Development and Application of Flux Cored Wire for Wire-Arc Additive Manufacturing of 460 MPa Grade Building Ten-Directional Steel Point

  DAI Yili, YU Shengfu, SHI Yusheng, LIU Shu

  Materials For Mechanical Engineering. 2019, 43(10): 24-29,52. https://doi.org/10.11973/jxgccl201910006

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Based on the nominal chemical composition of Q460 steel, the composition of a special flux cored wire was designed for the wire-arc additive manufacturing of building ten-directional steel point. The flux cored wire was prepared and its process performance was studied. The building ten-directional steel point was fabricated by the wire-arc additive manufacturing technique with this flux cored wire, and the dimensional accuracy, microstructure and mechanical properties were studied. The results show that the flux cored wire prepared by the experiments had stable arc and small spatter during the wire-arc additive manufactuning. No cracks, pores and other defects were formed in the depositing metal. The forming accuracy of the ten-directional building steel point by the wire-arc additive manufacturing with the flux cored wire met the requirements. The microstructure consisted of fine ferrite and little pearlite. The tensile properties and impact performance at room temperature and -40℃ met the mechanical property requirements of the traditional building ten-directional steel point of Q460 steel.
• Select
  Fatigue Property and Fracture Mechanism of 5754 Aluminum Alloy GTAW and FSW Joints

  QIAO Yaxia, ZHAO Lei, XU Lianyong, ZHANG Hao, ZHANG Pengfei, HAN Yongdian

  Materials For Mechanical Engineering. 2019, 43(10): 30-34,40. https://doi.org/10.11973/jxgccl201910007

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  5754 aluminum alloy with thickness of 10 mm was welded by gas tungsten arc welding (GTAW) and friction stir welding (FSW) using a double-sided synchronization welding method. The fatigue property of welded joints at stress amplitudes of 162, 135, 117, 108,99 MPa was compared and studied, and fracture mechanism was analyzed. The results show that the fatigue strength of GTAW joint at given stress amplitudes was obviously larger than that of FSW joint. The fatigue strength eigenvalues at 50% and 95% survival percent of GTAW joint increased by 26.3% and 24.4%, respectively, compared with those of FSW joint, indicating that the fatigue property of GTAW joint was better than that of FSW joint. The fatigue failure mechanism of GTAW and FSW joints was almost the same. The fatigue cracks all initiated at the outer surface of fusion zone of joints. With the decrease of stress amplitude, the proportion of the fatigue crack propagation zone increased. At the same stress amplitude, the proportion of crack propagation zone of GTAW joint was larger than that of FSW joint. The spacing of fatigue striations in GTAW joint was narrower, indicating that the fatigue life of GTAW joint was larger than that of FSW joint.
• Select
  Microstructure and Mechanical Properties of Single-and Double-Pass Friction Stir Welded T-Joints of 5083/6082 Dissimilar Aluminum Alloys

  ZHOU Faquan, JI Hua, DENG Jianfeng, LI Wenxiao, GUO Weiqiang, XU Hongyong, HONG Xiaoxiang

  Materials For Mechanical Engineering. 2019, 43(10): 35-40. https://doi.org/10.11973/jxgccl201910008

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  T-joints of 5083-O (wall plate)/6082-T6 (rib plate) dissimilar aluminum alloys were prepared by single-pass and reversed double-pass friction stir welding, and the microstructure and mechanical properties were studied. The results show that the lap interface of single-pass welded joints consisted of unconnected zone, effectively connected zone and kissing bond zone. After reversed double-pass welding, the kissing bond zone disappeared, and the effectively connected zone was broadened. The single-and double-pass welded joints both fractured in the base metal of the wall plate during T-direction tensile with the similar tensile strength, and fractured at the interface and in the heat affected zone of the rib plate, respectively, during L-direction tensile; moreover the double-pass welded joint had higher tensile strength. The single-pass welded joint yielded during the advancing side bending while brittlely fractured during the retreating side bending; the double-pass welded joint yielded during the advancing and retreating side bending. The microhardness of the single-and double-pass welded joints along the wall plate direction was kept at about 75 HV, and that along the rib plate direction decreased first, then increased and then was stabilized from the thermo-mechanical affected zone to the base metal.
• Select
  Effect of Accumulative Roll Bonding Process on Microstructure and Properties of AA3003 Aluminum Alloy

  LAI Chunming, LI Zezhi, QIN Nan, ZHANG Maiqiu, WANG Ming

  Materials For Mechanical Engineering. 2019, 43(10): 41-46. https://doi.org/10.11973/jxgccl201910009

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  AA3003 aluminum alloy sheet was processed by accumulative roll bonding with four passes. The microstructure, tensile properties and formability of the aluminum alloy sheet after different-pass accumulative roll bonding were studied. The results show that with the increase of roll bonding pass, the grains in the aluminum alloy sheet were refined and tended to be equiaxed, and the homogeneity of the microstructure increased in the sheet thickness direction. The rolling texture and shear texture were dominant in the central layer and the surface layer of the accumulative roll bonded aluminum alloy sheet, respectively. The accumulative roll bonding process improved the strength of the aluminum alloy sheet, but reduced the plasticity and formability. With the increase of roll bonding pass, the yield strength and tensile strength of the aluminum alloy sheet increased, the elongation changed little and the formability decreased slightly.
• Select
  Corrosion Behavior of Strip Casting B480GNQR Weathering Steel

  WU Jianchun, FANG Yuan

  Materials For Mechanical Engineering. 2019, 43(10): 47-52. https://doi.org/10.11973/jxgccl201910010

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Corrosion behavior of strip casting B480GNQR weathering steel was studied by 72 h alternate immersion accelerated corrosion test and electrochemical test in 0.01 mol·L^-1 NaHSO₃ solution, and compared with those of B800NQ weathering steel and DOCOL700 weathering steel as well as low carbon Q345B steel. The results show that the loss of mass per unit area of strip casting B480GNQR weathering steel was 11.888 mg·cm^-2 and the corrosion rate was 43% relative to low carbon Q345B steel. Strip casting B480GNQR weathering steel among the four bare steel samples had the highest free corrosion potential, indicating that it had the best corrosion resistance; its electrochemical impedance spectroscopy was characterized by the single capacitance resistance arc with a time constant. Strip casting B480GNQR weathering steel among the four rusty steel samples had the highest free corrosion potential, indicating that it had the best corrosion resistance; its electrochemical impedance spectroscopy was characterized by a capacitance resistance arc at the high frequency end and a diffusion arc of approximate 45° segment at the middle and low frequency ends. Phosphorus content at the location of 150~200 μm away from strip casting B480GNQR weathering steel casting band surface was the highest, showing typical negative segregation of phosphorus element, which greatly promoted the corrosion resistance.
• Select
  Effect of Cooling Rate on Microstructure and Mechanical Properties of X80 Pipeline Steel

  MA Jing, LI Wenjie, MA Anbo, ZHOU Peng, AN Na

  Materials For Mechanical Engineering. 2019, 43(10): 53-58. https://doi.org/10.11973/jxgccl201910011

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  X80 pipeline steel was heated to above the austenitizing temperature (920℃), held for 7 min, and cooled in different cooling media (10wt% NaCl solution, tap water, engine oil, air, cooling rate decreased in turn). The microstructure and mechanical properties were studied. The results show that with decreasing cooling rate, the strength and hardness of the test steel decreased, the plasticity increased, and the impact energy increased first and then decreased. After cooling at relatively high rates (in NaCl solution and tap water), bainite ferrite and a few martensite laths were formed in the microstructure, and many dislocation structures and a few carbides were found in martensite laths; the test steel had high strength and low deformability. After cooling at a relatively low rate (in air), polygonal ferrite, bainite ferrite and a few block martensite-austenite structures were formed in the microstructure; the strength and impact toughness of the test steel were low. After cooling at a moderate rate (in engine oil), a duplex structure of bainite and ferrite was formed in the microstructure; the multitude direction distributed bainite and high density dislocation ferrite adjacent to bainite led to good comprehensive mechanical properties and high resistance to large deformation of the test steel.
• Select
  Effects of Different Element Content on Precipitate Behavior of Precipitates in Haynes282 Alloy

  WANG Jinglin, YAO Zhihao, DONG Jianxin, JIANG He

  Materials For Mechanical Engineering. 2019, 43(10): 59-65. https://doi.org/10.11973/jxgccl201910012

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Thermodynamic calculation was conducted on Haynes282 alloy by using JMatPro software, and then the content of different precipitates in the alloy from 1 400℃ to 600℃ was obtained. The effects of chromium, cobalt, molybdenum, titanium, aluminum, carbon and boron on the precipitate behavior of precipitates were analyzed. The results show that the precipitate amount of carbides was mainly determined by carbon content. Chromium could enhance the stability of M₂₃C₆. Chromium, cobalt, molybdenum, titanium and aluminum could promote the precipitation and stability of σ phase. The increase of molybdenum content could promote the precipitation of μ phase, while boron, cobalt, chromium, titanium and aluminum inhibited the precipitation of μ phase. Boron had no effect on the stability of M₃B₂, but the increase of content improved the precipitate amount. Titanium contributed to the precipitation and stability of γ' phase, and aluminum improved the precipitate amount of γ' phase.
• Select
  Flow Stress Constitutive Equation of As-cast GCr15SiMn Bearing Steel

  PAN Guangyong, LUO Zhumei, LIN Chunlei

  Materials For Mechanical Engineering. 2019, 43(10): 66-70. https://doi.org/10.11973/jxgccl201910013

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Hot-compression test of as-cast GCr15SiMn bearing steel was carried out on a Gleeb-3500 thermal simulator. The effects of deformation temperature (1 223-1 423 K) and strain rate (0.1-10.0 s^-1) on flow stress were studied, and the microstructure was observed. The flow stress constitutive equation of the test steel was established by fitting the experimental data on the basis of the Arrhenius equation given by TEGART and SELLARS, and was verified. The results show that when deforming under test conditions, all the flow curves of the test steel showed a dynamic recrystallization characteristic; increasing the deformation temperature or reducing the strain rate could reduce the flow stress. At the strain rate of 1.0 s^-1, increasing the deformation temperature helped the dynamic recrystallization of the test steel and coarsened the grains. At the deformation temperature of 1 423 K and the strain rates of 0.1-1.0 s^-1, the greater the strain rate, the finer the dynamic recrystallized grains. The peak stresses were predicted by the established flow stress constitutive equation. The average relative error between the calculation value and the test value was 0.393%, indicating that the constitutive equation was relatively accurate.
• Select
  Fracture Cause of Inconel783 Alloy Bolt in Medium-Pressure Control Valve of an Ultra-supercritical Unit

  LUO Chang, QIAN Yujun, LIU Junjian, WU Yue, WANG Yan

  Materials For Mechanical Engineering. 2019, 43(10): 71-74,78. https://doi.org/10.11973/jxgccl201910014

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  Inconel783 alloy bolts in the medium-pressure valve of an ultra-supercritical unit fractured during service under high temperature and high pressure conditions. The cause of fracture was studied by macroscopic inspection, microstructure analysis, mechanical property test and phase analysis. The results show that the bolts fractured in a stress-accelerated grain boundary oxidation brittle fracture mode. Improper heat treatment of the bolt resulted in incomplete austenite grain boundaries without continuous β-AlNi phase. When the bolt was used under high temperature and high stress conditions, oxygen diffused along the grain boundary rapidly under stresses, resulting in the embrittlement of grain boundaries; therefore the intergranular cracks were initiated. The cracks propagated, and eventually led to the fracture of the bolt.
• Select
  Reason for Fracture of Commercial Vehicle Engine Timing Chain during Inspection after Long Storage

  XUE Xicai, SHAO Baiming, ZHU Lingbin

  Materials For Mechanical Engineering. 2019, 43(10): 75-78. https://doi.org/10.11973/jxgccl201910015

  Abstract ( ) Download PDF ( )   Knowledge map   Save

  An commercial vehicle engine suddenly stalled and could not start over a pre-sale inspection after long storage. After investigation, it was found that a timing chain fractured. The reason for fracture of the timing chain was studied by fracture morphology and microstructure observation, chemical composition analysis, hardness testing, and so on. The results show that during the storage, the stress corrosion fracture occured at one side of internal chain piece pin hole of the timing chain by the combination of vapor corrosion and tension stress, and then the fatigue fracture occured at the other side of the pin hole by working loads.