20 January 2020, Volume 44 Issue 1
    

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  • Research Progress on Influence of Service Environment on Fatigue Damage Behavior of High Strength Aluminum Alloy
    CHEN Yuqiang, ZHANG Hao, ZHANG Wentao, PAN Suping, LIU Wenhui, SONG Yufeng
    Materials For Mechanical Engineering. 2020, 44(1): 1-7. https://doi.org/10.11973/jxgccl202001001
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    The research status of fatigue damage behavior of high strength aluminum alloys under different environments from the aspects of temperature, humidity, corrosion medium, gaseous medium, loading condition are reviewed, and the effect mechanisms of environment factors on fatigue damage behavior of high strength aluminum alloys are revealed. The problems and future development direction about the fatigue damage behavior research of high strength aluminum alloy are pointed out.
  • Effect of KOH Content on Structure and Bonding Strength of Red Mud Plasma Electrolytic Oxidation Composite Ceramic Coatings
    LIU Shifeng, ZENG Jianmin
    Materials For Mechanical Engineering. 2020, 44(1): 8-15. https://doi.org/10.11973/jxgccl202001002
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    Plasma electrolytic oxidation (PEO) of 5005 aluminum alloy was carried out in KOH-red mud electrolytes. Effects of KOH mass concentration (CKOH=1.0, 2.0, 3.0, 4.0, 5.0 g·L-1) on the critical arcing voltage of PEO and the thickness, phase composition, morphology and bonding strength of the ceramic coating were analyzed. The results show that the ceramic coatings prepared in electrolytes with different KOH content were mainly composed of γ-Al2O3 and α-Al2O3, but a small amout of CaCO3, SiO2 and Fe2O3 phases also appeared. When KOH content increased, the positive and negative critical arcing voltages of PEO decreased rapidly; the coating thickness showed a growth trend of "semi-parabolic" shape; the γ-Al2O3 content in the ceramic coating increased first, then decreased and then increased, the change trend of α-Al2O3 content was just the opposite, and the CaCO3, SiO2, Fe2O3 content increased first and then decreased; the surface porosity of the ceramic coating decreased first and then increased, the surface roughness kept increasing and the hardness and bonding strength increased first and then decreased.
  • Effect of Crack Source Location on High Cycle Fatigue Life of 6005A Aluminum Alloy Extruded Profiles
    ZHANG Lan, ZHAO Hongjin, LI Shengci, YE Qing, LI Dehua
    Materials For Mechanical Engineering. 2020, 44(1): 16-20,28. https://doi.org/10.11973/jxgccl202001003
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    The effect of crack source location on high cycle fatigue life of 6005A-T6 aluminum alloy extruded profiles was studied by high cycle fatigue tests. The results show that the median fatigue strength of 6005A-T6 aluminum alloy extruded profiles was 164.5 MPa at the stress ratio of 0.1; the fatigue strength was relatively high, but the fatigue life distribution was relatively dispersal. Under the maximum stress of 200 MPa, the fatigue crack source region of samples with different fatigue lives was small; the fatigue crack propagation region consisted of fatigue strips and secondary cracks; the area of transient fracture region was large, and the region consisted of holes and dimples. The main reason for the difference in fatigue life under the same maximum stress was the difference location of fatigue crack source. Under the maximum stress of 200 MPa, the fatigue life of the sample with fatigue crack source in holes was the longest, which was one order of magnitude larger than that with fatigue crack source on oxide inclusions, and the fatigue life of the sample with the fatigue crack source in Al7(CrFe) second phase particles was between the two.
  • Shear Rheological Properties of Polyurethane-Based Magnetorheological Gel
    YANG Huijing, CHEN Wei, CHEN Dong, ZHANG Guang
    Materials For Mechanical Engineering. 2020, 44(1): 21-28. https://doi.org/10.11973/jxgccl202001004
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    Polyurethane-based magnetorheological gels (MRG) with different mass fractions of carbonyl iron powder (50%,70%,80%) were prepared. The static and dynamic shear rheological properties of the MRG with a wide shear stress range under different magnetic induction intensities, shear rates and strain amplitudes were studied, and Herschel-Bulkley constitutive model parameters were identified based on the test results. The results show that the shear stress of MRG with 80wt% carbonyl iron powder had the widest range, and megnetorheological effect was the most obvious. The yield shear stress of MRG with 80wt% carbon iron powder increased with the magnetic induction intensity; the kinetic viscosity at different magnetic induction intensities decreased with the increase of shear rate. The MRG was a non-Newtonian fluid with yield shear stress and shear thinning characteristics, and its rheological properties satisfied Herschel-Bulkley shear thinning model. The storage or loss modulus was greatly affected by the shear strain amplitude and magnetic induction intensity, but had a weak dependence on the frequency. The megnetorheological effect and linear viscoelastic critical strain amplitude both increased with the increase of magnetic induction intensity. The effect of magnetic induction intensity on normal stress was more significant than that of shear rate and shear strain amplitude.
  • Effect of Heat Input and Annealing Holding Time on Grain Size of Overheating Area in 409L Ferritic Stainless Steel TIG Welded Joint
    ZHAO Zhenzhen, GUO Yonghuan, ZHAO Jianye, JIANG Peng, FAN Hui
    Materials For Mechanical Engineering. 2020, 44(1): 29-32. https://doi.org/10.11973/jxgccl202001005
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    409L ferritic stainless steel plates were welded by tungsten inert gas arc (TIG) welding under different heat inputs (1 145.5-5 248.0 J·mm-1), and then the joints were annealed at 830℃ for different holding times (0-13 min). The effect of heat input and annealing holding time on microstructure and grain size of the overheating area of joints was studied by homogeneous design method. The results show that the microstructures of the overheating area of welded joints before and after annealing were both coarse ferrite under different heat inputs, and with the increase of heat input, network ferrite and wisterite were found in the microstructure. The grain size of the overheating area of joints after annealing was almost the same as that before annealing. When the heat input increased from 1 145.5 J·mm-1 to 5 248.0 J·mm-1, the grain size of the overheating area increased from 58.64 μm to 160.97 μm. The annealing holding time had little effect on the grain size. The heart input had a nonlinear effect on the grain size of overheating area, and the effect was much larger than that of annealing holding time.
  • Microstructure and Filler Metal Element Diffusion Behavior of TiZrCuNi Filler Metal Vacuum Brazing Pure Titanium TA1 Joint Interface
    LIU Song
    Materials For Mechanical Engineering. 2020, 44(1): 33-38. https://doi.org/10.11973/jxgccl202001006
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    The microstructure and filler metal element diffusion behavior of brazing joint interface were studied after titanium TA1 was vacuum brazed with Ti-37.5Zr-15Cu-10Ni titanium-based amorphous filler metal. The results show that the brazing joints consisted of brazing joint, interface region between brazing joint and base metal, diffusion region of small needle and strip, diffusion region of dense flake and diffusion region of large flake, and the corresponding microstructures were β phase, β phase+small strip α phase, widmanstatten, coarse widmanstatten+(Ti, Zr)2(Cu, Ni) intermetallic compound and α phase+Ti2(Cu, Ni)+TiNiFe intermetallic compound, respectively. The diffusion distance to titanium matrix of Ni was the longest, the diffusion distance of Cu was the second, and the diffusion distance of Zr was the shortest. Zr could form continuous solid solution with α-Ti and β-Ti, but the ability of β phase to dissolve Zr atoms was stronger than that of α phase; Cu and Ni were mainly both solubilized in β phase.
  • Dynamic CCT Behaviour of 600 MPa Grade Hot-Rolled Dual Phase Steel and Optimization of Hot-Rolled Coiling Process
    ZHAO Nan, LIU Xuewei, SUN Mingjun, HUANG Xuchuan
    Materials For Mechanical Engineering. 2020, 44(1): 39-43,56. https://doi.org/10.11973/jxgccl202001007
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    The chemical composition of medium temperature coiling type hot-rolled dual phase steel was designed by appropriately reducing the content of chromium and molybdenum elements on basis of the composition of traditional 600 MPa grade dual phase steel. The dynamic continuous cooling transformation behaviour of the test steel was analyzed by thermo-simulation. The hot-rolled coiling process was optimized according to the thermo-simulation results, and a trial industrial production was conducted. The microstructure and properties before and after optimization were studied. The results show that when the cooling rate was greater than 15℃·s-1, the microstructure of the test steel mainly consisted of ferrite, martensite and a small amount of bainite; with the increase of cooling rate, bainite changed from granular to lath-shape, and martensite content increased. The grains of hot-rolled dual phase steel produced by optimal medium temperature coiling whole intensive cooling process was finer than that before optimization, and martensite content was higher. The yield strength, tensile strength and hardness of hot-rolled dual phase steel produced by optimal process were all higher than those before optimization; percentage elongation after fracture and hole expansion rate were both lower than those before optimization, but still satisfied the standard requirement, indicating that trial-produced hot-rolled dual phase steel had good comprehensive mechanical properties.
  • Microstructure and Properties of Ni-Fe-base Superalloy for 700 ℃ Advanced Ultra Supercritical Unit Final Superheater
    YUAN Yong, DANG Yingying, YANG Zhen, ZHANG Peng, YIN Hongfei, HUANG Jinyang, ZHOU Yongli, YAN Jingbo, LU Jintao, GU Yuefeng, ZHAO Haiping, WANG Tingting, XU Songqian
    Materials For Mechanical Engineering. 2020, 44(1): 44-50. https://doi.org/10.11973/jxgccl202001008
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    The microstructure and properties of a new Ni-Fe-base HT700T superalloy for 700℃ A-USC unit final superheater were studied. The results show that HT700T alloy was a precipitation-hardening alloy, and the microstructure stability of HT700T alloy at 750℃ was stable. The yield strength at 750℃ was 598 MPa, and remained about 400 MPa after thermal exposure for 3 000 h. The creep rupture strength of the alloy at 750℃/105 h was 103 MPa. The impact energy at room temperature of the alloy after thermal exposure at 750℃ for 104 h was 50 J·cm-2, which was slightly lower than that before thermal exposure. The resistance to steam oxidation at 750℃ reached the complete oxidation resistance level, and the metal corrosion thickness in simulated flue gas and coal ash at 750℃/2×105 h was 0.2 mm. The comprehensive performance of HT700T alloy could basically meet the service performance requirements of 700℃ A-USC unit final superheater; the industrial manufactured alloy boiler tube had been running normally on the test platform for over 15 000 h.
  • Effect of Laser Bulk Energy Density on Densification Behavior of TC4 Titanium Alloy by SLM
    SUN Jing, ZHU Xiaogang, LI Peng, WANG Xuqin, QIU Lianfang, WANG Fei, WANG Lianfeng, WU Wenheng, GU Zheming
    Materials For Mechanical Engineering. 2020, 44(1): 51-56. https://doi.org/10.11973/jxgccl202001009
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    The TC4 titanium alloy was prepared by selective laser melted (SLM) technique, and the effect of laser bulk energy density on surface quality and densification behavior of the alloy was studied. The results show that when the laser bulk energy density increased from 33 J·mm-3 to 80 J·mm-3), the surface roughness of the alloy decreased, indicating the surface quality was improved; the surface balling effect was improved significantly. With the increase of the laser bulk energy density, the amount of voids inside the alloy decreased and the relative density increased from 90.5% to 99.3%; but excessive flow of the melt at an over high laser bulk energy density affected the dimensional accuracy and properties of the formed parts. The optimum parameter for preparing the alloy was the laser bulk energy density of laser 66 J·mm-3, namely the laser effect of 250 W and scanning velocity of 500 mm·s-1, and the alloy had good surface quality and densification.
  • Microstructure and Tensile Properties of Arc Additive Manufacturing 4043 Aluminum Alloy Thin-Walled Parts by CMT with Addition of Pulse
    JIANG Qi, ZHANG Peilei, LIU Zhiqiang, YU Zhishui, SHI Haichuan
    Materials For Mechanical Engineering. 2020, 44(1): 57-61. https://doi.org/10.11973/jxgccl202001010
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    4043 aluminum alloy thin-walled parts were obtained by arc additive manufacturing under the conditions of cold metal transition with addition of pulse (CMT+P). The forming performance of thin-walled parts prepared under different parameters were compared. The microstructure and tensile properties of thin-walled parts with good forming performance were studied, and compared with those prepared by CMT process. The results show that when the welding speed was 8 mm·s-1 and wire feeding speed was 4 m·min-1, the forming performance of thin-walled parts prepared by CMT+P process was the best, and the forming effect was close to that prepared by CMT process. The microstructure of single layer of thin-walled parts prepared by CMT+P process consisted of fine-grained area in the upper layer and coarse-grained area in the lower layer, and there were coarse columnar dendrites growing through the interface between weld beads. The microstructure prepared by CMT process was fine columnar crystals with uniform distribution. The tensile properties of thin-walled parts prepared by CMT+P process were better than those under CMT process condition. The fracture modes of longitudinal and transverse tensile samples under CMT+P process condition were both ductile fracture and anisotropy percentage of longitudinal and transverse tensile streagth was only 4%, indicating there was no anisotropy in mechanical properties of thin-walled parts.
  • Microstructure and Mechanical Properties of In-situ Synthesized TiC and TiB Reinforced Titanium Matrix Composites
    XU Huan, GUO Xianglong, Lü Weijie
    Materials For Mechanical Engineering. 2020, 44(1): 62-67,73. https://doi.org/10.11973/jxgccl202001011
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    The different contents of in-situ synthesized TiC, TiB and TiC+TiB (volume proportion of 1:1)/Ti titanium matrix composites were prepared by vacuum consumable melting, forging and annealing process, and the microstructure, tensile properties at room temperature and high temperature (300℃) and compression properties at room temperature were studied. The coupling relationship between the strengthening effects of TiC and TiB during stretching at room temperature was analyzed. The results show that the matrix structure of composites was deformed α structure; TiC presented fine equiaxed shape and slightly thick ellipsoidal shape, and TiB presented short fiber shape. When the total volume fraction of reinforcements was fixed, the strengthening effect of TiC and TiB was higher than that of TiC or TiB, and increased with the increase of volume fraction of reinforcements; however, the plasticity of composites decreased obviously. The main tensile fracture mode of composites at room temperature was bearing failure of reinforcements, while the fracture mode at high temperature included bearing failure of reinforcements and debonding of some TiB short fibers with matrix. The relationship of strengthening effects between TiC and TiB reinforcements and fine-grain met the superposition of coupling coefficient of 1.5 during stretching at room temperature.
  • Effect of Sintering Temperature on Structure and Properties of Powder Metallurgy Fe-Cu-C Alloy under Industrial Condition
    LUO Haiyu, LIU Bo, HUANG Zhihong, YANG Xiaokang
    Materials For Mechanical Engineering. 2020, 44(1): 68-73. https://doi.org/10.11973/jxgccl202001012
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    Fe-Cu-C alloy was prepared by powder metallurgy technology under practical industrial condition, and the effect of sintering temperature (1 060-1 160℃) on density, microstructure, phase composition and mechanical properties of the alloy was studied. The results show that with the increase of sintering temperature, the density of the alloy increased first and then decreased, and reached the maximum value of 7.02 g·cm-3 at 1 140℃. With the increase of sintering temperature, the spherification degree of particles in structure of the alloy increased, and the mount and size of pores both decreased; the microstructure tended to be stable; the diffraction peak of copper phase disappeared, while the Fe4Cu3 phase appeared. The tensile strength and hardness had the same trend with sintering temperature as that of density, and both reached the maximum values of 460 MPa and 185 HRB at 1 140℃, respectively; all tensile fractures were mainly characterized by brittle fracture. The mechanical property indexes of the prepared alloy indexes industrial condition were almost the same with those under laboratory condition.
  • Effect of Post-Weld Cooling Method on Performance of S20433 Austenitic Stainless Steel Plasma Arc Welded Joint
    WANG Weidong, BI Zongyue, XU Xueli
    Materials For Mechanical Engineering. 2020, 44(1): 74-77. https://doi.org/10.11973/jxgccl202001013
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    S20433 austenitic stainless steel plate was welded by plasma arc welding, and the microstructure and properties of joints by post-weld air cooling and water cooling methods were studied. The results show that the ferrite content in the joint by water cooling method was higher than that by air cooling method, and the heat affected zone was narrower. The hardness of the joint by water cooling method was slightly higher than that by air cooling method. The tensile strengths of joints by air cooling and water cooling methods were 693, 667 MPa, respectively, and the joint by air cooling method had better strength matching with base metal. No cracks appeared in the joint by air cooling method after bending tests, but the joint by water cooling method cracked during root bend tests due to the presence of oxide inclusions, indicating that joints by air cooling method had better toughness. The joints by two cooling methods both had good resistance to hydrogen-induced cracking. The joint by post-weld air cooling method had better comprehensive performance.
  • Cause of Scarring on Surface of 55SiCr Spring Steel Wire
    PAN Sheng, WANG Junyi, LIU Xinkuan, SHENG Rongsheng, LI Wenjun, FANG Zhou, CHEN Jie
    Materials For Mechanical Engineering. 2020, 44(1): 78-82. https://doi.org/10.11973/jxgccl202001014
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    During production of 55SiCr spring steel wire, the surface of the steel wire was scarred after shot peening and drawing. The reasons for scarring were analyzed by morphology observation, chemical composition analysis, microstructure observation and microhardness test. The results show that the surface scabs were formed during shot peening. During the long-term service, cast steel shots appeared angular and work hardening resulting in the reduction of toughness and increase of brittleness; cast steel shots were easy to crack, and then residual particles formed. During shot peening, residual particles of cast steel shot tended to be embed in the matrix of steel wire, leading to the surface scratches and deformation to form massive scarring on surface of steel wire during following drawing process.
  • Fracture Cause of Dissimilar Steel Tube Welded Joint of Final Boiler Reheater in a Power Plant
    LIU Kexiu, FENG Xiaoliang, MA Kuo, LU Zhongming, WANG Lian
    Materials For Mechanical Engineering. 2020, 44(1): 83-86. https://doi.org/10.11973/jxgccl202001015
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    12Cr1MoVG/TP304H dissimilar steel tube welded joint of final boiler reheater in a power plant fractured during service, and the fracture cause was analyzed by macroscopic morphology observation, chemical composition analysis, mechanical property test, microstructure observation, micro-area composition analysis. The results show that the brittle fracture occurred in dissimilar steel tube welded joints along the fusion line on 12Cr1MoVG steel tube side. After long-term service at high temperature, the carbon in the welded joint diffused and migrated, and then the carbide concentrated near the fusion line on 12Cr1MoVG steel tube side distributed along the grain boundaries; meanwhile, micro creep cracks formed, which seriously weakened the strength and toughness of the region. The thermal conductivity and the coefficient of linear expansion between 12Cr1MoVG steel and TP304H steel was very different, resulting in the formation of large thermal stress in the high temperature environment. Finally, the dissimilar steel welded joint underwent brittle fracture along the fusion line on 12Cr1MoVG steel tube side under the combination of high temperature steam pressure and thermal stress.
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