20 March 2020, Volume 44 Issue 3
    

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  • Effect of Al-Cu Alloy Sheet on Microstructure and Properties of Steel/Aluminum Dissimilar Metal Laser-MIG Hybrid Welded Joint
    WU Yongliang, GU Lixia, LUO Lifeng
    Materials For Mechanical Engineering. 2020, 44(3): 1-7,12. https://doi.org/10.11973/jxgccl202003001
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    The dissimilar metal welding of Q890 steel/6063 aluminum alloy was carried out by laser-MIG hybrid welding process controlled by PLC system. The effect of the addition of Al-Cu alloy sheet to the steel side groove surface on the microstructure, hardness and tensile properties of the joint was studied. The results show that the laser-MIG hybrid welded joint had typical brazing characteristics. The interface layer of the joint without Al-Cu alloy sheets was composed of tongue-like Fe2Al5 phase and coarse needle-like Fe4Al13 phase with a thickness of about 18 μm. The interface layer with Al-Cu alloy sheet was composed of tongue-like (Fe,Cu)2Al5 phase and fine flocculent (Fe,Cu)4Al13 phase with a thickness of about 9 μm, and the microstructures of weld zone and the heat-affected zone were similiar with those without Al-Cu alloy sheet. The hardness of the interface layer of the joint with Al-Cu alloy sheet was about 59 HV lower than that without Al-Cu alloy sheet. The tensile strength of the joint with Al-Cu alloy sheet was 109.8% higher than that without Al-Cu alloy sheet; the fracture location of joints with and without Al-Cu alloy sheet both occurred in the interface layer.
  • Effect of Adding Cr, Al, Ti and Ni Alloy Elements on Properties of Fe-17Mn Damping Alloy
    CAO Ping, CAI Zhigang
    Materials For Mechanical Engineering. 2020, 44(3): 8-12. https://doi.org/10.11973/jxgccl202003002
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    5wt%Cr, 1wt%Al, 1wt%Ti or 1wt%Ni were added to the Fe-17Mn binary alloy which had the best damping property, and then Fe-Mn, Fe-17Mn, Fe-17Mn-5Cr-1Al, Fe-17Mn-5Cr-1Ti and Fe-17Mn-5Cr-1Ni alloys were prepared by vacuum induction smelting. After forging and solution treatment, the effect of Cr, Al, Ti, Ni elements on damping property, mechanical properties and corrosion resistance of the alloys was studied. The results show that after adding Cr element, the strength of the alloy increased significantly and the corrosion resistance was improved; the damping property increased at low strain amplitude (200×10-6-900×10-6), and decreased at high strain amplitude (greater than 900×10-6). The corrosion resistance of the alloy after adding 1wt% Al element or Ti element into Fe-17Mn-5Cr alloy changed little, but the strength decreased; the damping property of the alloy after adding Ti became worse, but the damping property after adding Al changed little. Compared with Fe-17Mn alloy, the strength and the damping property of the alloy after adding 1wt%Ni element into Fe-17Mn-5Cr alloy changed little; the corrosion resistance was reduced slightly, but still better than that of Fe-17Mn alloy. Fe-17Mn-5Cr-1Ni alloy had the best comprehensive properties.
  • Effect of Na2CO3/C6H12O6 in Electrolyte on Microstructure and Corrosion Resistance of AZ31 Magnesium Alloy Anodized Film
    ZHANG Fenggang, SONG Peiwei, WANG Yongshan
    Materials For Mechanical Engineering. 2020, 44(3): 13-17. https://doi.org/10.11973/jxgccl202003003
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    After adding different content of Na2CO3 and C6H12O6 into NaOH-Na2SiO3-Na2B4O7 basic electrolyte, AZ31 magnesium alloy was treated by direct current anodizing and then the microstructure and corrosion resistance in neutral salt spray of the magnesium alloy anodized film were studied. The results show that all magnesium alloy anodized film consisted of MgO and Mg2SiO4 phase. After adding Na2CO3 and C6H12O6 into electrolyte, the micropores evenly distributed on the surface of the anodized film, and the size decreased; the thickness of the anodized film increased. When the mass concentration of Na2CO3 increased from 10 g·L-1 to 30 g·L-1, the size of micropores increased, and the thickness of anodized film decreased. When the mass concentration of C6H12O6 increased from 5 g·L-1 to 15 g·L-1, the size of micropores decreased, and the thickness of anodized film increased. The main corrosion form of magnesium alloy anodized film was pitting, which presented a distribution of fluvial pattern. After adding 10 g·L-1 Na2CO3 into the electrolyte, the micropores had the smallest size with the diameter of 1-3 μm, and the thickness of the anodized film reached 16 μm; the anodized film had relatively good corrosion resistance.
  • Effect of High Voltage Direct Current Electric Field on Corrosion Behavior of 5052 Aluminum Alloy Under Simulated Seawater Cyclic Wet-Dry Condition
    CAI Jianbin, CAI Zhencai, ZHUANG Jianhuang, LIN Deyuan, CHEN Yunxiang, SHAO Yanqun, ZHENG Yuesheng
    Materials For Mechanical Engineering. 2020, 44(3): 18-24,31. https://doi.org/10.11973/jxgccl202003004
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    The corrosion behavior of 5052 aluminum alloy under simulated seawater (3.5wt% NaCl solution) cyclic wet-dry condition at direct current electric field intensity of 0-400 kV·m-1 was studied. The results show that with the increase of electric field intensity, the mass loss per unit area and corrosion rate of aluminum alloy increased. With the increase of corrosion time, the mass loss per unit area increased, but the corrosion rate decreased. In the early corrosion (0-7 d), the pitting occurred on the surface of aluminum alloy; with the increase of electric field intensity, the pitting was intensified. In the middle stage of corrosion (7-15 d), the exfoliation corrosion occurred; the larger the electric field intensity, the more serious the peeling. In the late stage of corrosion (15-30 d), the passivation, passive film cracking, micro-couple corrosion, exfoliation corrosion alternately occurred.
  • Effect of Heat Treatment on Microstructure and Corrosion Resistance of Plasma Sprayed Fe-based Amorphous Alloy Coating
    WANG Qijie, YI Yu, WANG Miqi, JIANG Siqi, WU Lintao, ZHOU Zehua, YANG Guangheng
    Materials For Mechanical Engineering. 2020, 44(3): 25-31. https://doi.org/10.11973/jxgccl202003005
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    Fe48Cr15Mo14C15B6Y2 amorphous alloy coating was prepared on Q235 steel substrate by plasma spraying technique, and the coating was heat treated at 200, 300, 500, 600, 700℃. The effect of heat treatment on the microstructure, electrochemical corrosion resistance and uniform corrosion resistance of the coating was studied. The results show that with the increase of heat treatment temperature, the amorphous phase content in the coating decreased, and the porosity decreased first and then increased; the porosity of the coating heat-treated at 300℃ was the lowest, and lower than that of the unheat-heated coating. The crystal phases in the coating after heat treatment mainly included α-Fe, Fe-Cr, Fe63Mo37, Fe3C. With the increase of heat treatment temperature, the free corrosion current density of the coating decreased first and then increased; the free corrosion current density of the coating heat-treated at 300℃ was the smallest, and the electrochemical corrosion resistance was the best. After heat treatment, the mass loss per unit area of the coating immersed in NaCl solution for 31 d decreased; the higher the heat treatment temperature, the smaller the mass loss per unit area, indicating the uniform corrosion resistance of the coating was improved.
  • Effect of Structural Size on Fatigue Properties of 7050 Aluminum Alloy Lug
    SUN Weiwei, CAI Ling, ZHANG Jianbo, YUAN Lu, LIU Jianzhong
    Materials For Mechanical Engineering. 2020, 44(3): 32-35. https://doi.org/10.11973/jxgccl202003006
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    Fatigue tests at three stress levels were conducted on 7050 aluminum alloy lug samples with different sizes. The fatigue stress-life (S-N) curves of the lugs were obtained by the least square method. The effects of ratio of ear hole diameter to lug width d/W (d had a fixed value, 24 mm; d/W=0.67, 0.50, 0.40) and ratio of longitudinal margin to transverse margin of ear hole y/x (y/x=1.0, 1.6) on fatigue properties and fracture morphology of the lugs were studied. The results show that under the same stress, the fatigue life of 7050 aluminum alloy lugs increased first and then decreased with the decrease of d/W (namely increasing W). The larger of the y/x value, the longer of the fatigue life of the lugs. The fatigue fracture of the lugs with different sizes all had typical fatigue fracture characteristics. The cracks initiated on surfaces and at corners.
  • Fretting Wear Property of 25CrNi2MoV Steel
    HUANG Liman, ZHANG Yalong, QU Shengguan, QIN Haidi, LAI Fuqiang, LI Xiaoqiang
    Materials For Mechanical Engineering. 2020, 44(3): 36-41. https://doi.org/10.11973/jxgccl202003007
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    The fretting wear test of new type 25CrNi2MoV steel for high-speed and heavy-duty drive shaft was carried out by fretting friction and wear tester under dry friction condition. The fretting wear property of the steel under different loads (50-200 N) and frequencies (15-30 Hz) was studied. The results show that the average friction coefficient of 25CrNi2MoV steel decreased from 0.766 to 0.661, and the wear volume increased from 19.65×10-3 mm3 to 75.83×10-3 mm3 when the load increased from 50 N to 200 N at the frequency of 20 Hz. Under the load of 30 N, when the frequency increased from 15 Hz to 30 Hz, the average friction coefficient increased from 0.790 to 0.905, and the wear volume increased from 11.43×10-3 mm3 to 23.88×10-3 mm3. Under different test parameters, the oxidation and ploughing appeared on the wear surface of 25CrNi2MoV steel, indicating that the wear mechanism contained oxidation wear and abrasive wear. The wear mechanism of 25CrNi2MoV steel was mainly adhesive wear under the load of 50,100 N, and was fatigue wear under the load of 150, 200 N at the frequency of 20 Hz. Under the load of 30 N, the wear mechanism was mainly abrasive wear at the frequency of 15, 25 Hz, and was mainly fatigue wear at the frequency of 30 Hz.
  • Pore Structure and Mechanical Property of Porous Materials Prepared by Direct Sintering of Silicon Slag and Glass Powder
    JIANG Longxiang, LU Jinshan
    Materials For Mechanical Engineering. 2020, 44(3): 42-46,50. https://doi.org/10.11973/jxgccl202003008
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    Porous materials were prepared by the powder direct sintering method with silicon slag and glass powder as raw materials. The effect of sintering temperature (700-900℃), sintering time (15-120 min) and heating rate (10-100℃·min-1) on the apparent density, porosity, phase composition and compressive strength of the porous materials was investigated. The results show that the uniformity of pore structure deteriorated with the increase of sintering temperature. The apparent density decreased first and then increased with the increase of sintering temperature, increased with the extension of sintering time and decreased with the increase of heating rate. The variation of porosity was opposite to that of apparent density. The main phases of porous materials included glass phase and crystalline phases of Si, SiC, SiO2 and Ca2Al2SiO7, and the crystallinity decreased with the increase of sintering temperature. The compressive strength increased and then decreased with increasing sintering temperature. When the powder mixture was sintered at 750℃ for 30 min with heating rate of 30℃·min-1, the obtained porous material had main crystalline phases of Si and Ca2Al2SiO7, the maximum compressive strength of 1.60 MPa, the apparent density of 0.43 g·cm-3 and the porosity of 80%.
  • Effect of Cooling Temperature in Controlled Rolling and Cooling on Microstructure and Tensile Properties of Q550D High Strength Steel
    LEI Bo, HE Yu, HUANG Xianbin
    Materials For Mechanical Engineering. 2020, 44(3): 47-50. https://doi.org/10.11973/jxgccl202003009
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    Controlled rolling and cooling process was conducted on hot-rolled Q550D steel plates. The effect of six groups of start cooling temperatures and final cooling temperatures on the microstructure and tensile properties of the test steel was studied. The results show that the matrix microstructures of the test steel all consisted of bainite+ferrite+martensite/austenite (M/A) island at six groups of cooling temperatures. At the same finish cooling temperature, when the start cooling temperature decreased, the ferrite content in the test steel increased significantly and the M/A island content increased slightly; the yield ratio decreased. At the same start cooling temperature, when the finish cooling temperature decreased, the ferrite conten decreased slightly while the M/A island content increased obviously; the yield ratio increased. When the start cooling and finish cooling temperatures were lowered at the same time, the content of ferrite and M/A island increased synchronously, but the increase in M/A island content was smaller; the yield ratio decreased. The test steel had the best tensile properties at the start cooling temperature of 755℃ and finish cooling temperature of 395℃.
  • Properties of Tantalum Coating Prepared via Double Glow Plasma Surface Metallurgy Technique on Thick Diamond Film Surface
    LU Mingjie, ZHENG Ke, GAO Jie, HEI Hongjun, WU Yucheng, SHU Xuefeng, TANG Bin, YU Shengwang
    Materials For Mechanical Engineering. 2020, 44(3): 51-55. https://doi.org/10.11973/jxgccl202003010
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    Tantalum coating was prepared on mechanically polished thick diamond film via double glow plasma surface metallurgy technique. The surface and section morphology, micro-area composition, phase composition and bonding property of the coating were studied. The results show that the tantalum coating was continuous and uniform, consisting of tantalum metallic layer and compound layer at the interface. The coating thickness was about 1.7 μm, and the coating structure was composed of columnar crystal. A 1.1 μm thick diffusion zone with tantalum and carbon distributed in gradient was formed at the interface of the tantalum coating and the thick diamond film, and two compounds of TaC and Ta2C were formed here. The polishing scratches on the thick diamond film were filled up by tantalum atoms, and therefore reduced the surface roughness from 128 nm to 57 nm. The obtained tantalum coating had good plasticity and good bonding performance with the thick diamond film.
  • Intergranular Corrosion Performance at Pulse Current Crack Arresting Area of Austenitic Stainless Steel and Its Evaluation Method
    ZHANG Zhuwu, PAN Guangguo, JIANG Yan, XU Chengwei
    Materials For Mechanical Engineering. 2020, 44(3): 56-61,77. https://doi.org/10.11973/jxgccl202003011
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    The intergranular corrosion performance at pulse current crack arresting area of 304 stainless steel before and after sensitization was studied by oxalic acid electrolytic etching test and potentiostatic polarization test, and a method suitable for evaluating the intergranular corrosion performance at crack arresting area was determined. The results show that there was no carbide precipitated at grain boundaries in the solidification zone, fine-grained zone and deformed martensite zone at crack arresting area; after potentiostatic polarization, the passive film at grain boundaries was intact, indicating intergranular corrosion didn't occur at the crack arresting area. The corrosion occurred at grain boundaries of different areas at crack arresting area of the sensitized specimen, indicating that the oxalic acid electrolysis method failed to distinguish the difference in intergranular corrosion performance among different micro-zones after pulse crack arrest. After potentiostatic polarization test, the passivation films at grain boundaries in the solidification zone and fine-grained zone at crack arresting area of the sensitized specimen had better stability and a certain ability to resist intergranular corrosion. The severe intergranular corrosion occurred in the defermed martensite zone. The potentiostatic polarization method can be used to evaluate the intergranular corrosion performance at pulse current crack arresting area of austenitic stainless steels.
  • Numerical Simulation of Properties of Auxetic Elliptical Porous AlSi10Mg Alloy Prepared by Selective Laser Melting
    WANG Xiao, WANG Huaiming, QI Junfeng, LI Zhijie, ZHANG Yang
    Materials For Mechanical Engineering. 2020, 44(3): 62-67. https://doi.org/10.11973/jxgccl202003012
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    A simplified design method of auxetic elliptical porous material was pointed out with major/minor axis ratio and semi-minor axis length of ellipse, and initial cell edge length as design parameters. The mathematical model between Possion's ratio of the material and the design parameters was established by geometric relation, and the mathematical model between elastic moduli and design parameters was established on basis of Gibson-Ashby model. The Possion's ratio mathematical model of auxetic elliptical porous AlSi10Mg alloy prepared by selective laser melting technique was verified by quasi-static compressing experiments, and the constant C of the elastic moduli mathematical model was also determined. The results show that the Possion's ratios of auxetic elliptical porous AlSi10Mg alloy calculated by the mathematical model of Possion's ratio and design parameters were consistent with the test results, and the relative error was 10%-15%. The ratio of major/minor axis, semi-minor axis length were negatively correlated with Posssion's ratio, and the initial cell edge length was postively correlated with Possion's ratio. The constant C of the elastic moduli mathematical model of auxetic elliptical porous AlSi10Mg alloy obtained by calculation was about 4.123.
  • Finite Element Simulation of Mechanical Properties of Selective Laser Melted Ti-6Al-4V Alloy at High Strain Rates
    LI Ying, WANG Shaohui, ZHANG Ting, LIU Chuanxin, WU Haihui, CHAI Xianghai
    Materials For Mechanical Engineering. 2020, 44(3): 68-72. https://doi.org/10.11973/jxgccl202003013
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    Ti-6Al-4V alloy was prepared by selective laser melting (SLM) technique. After post vacuum annealing and hot isostatic pressing treatment, the mechanical properties of the alloy at quasi-static and high strain rates (500-3 000 s-1) were studied. The calibration of bi-linear material model was implemented; the obtained material parameters were applied to the finite element simulation of Hopkinson compression test, and the simulation results were compared with the test results. The results show that the microstructure of SLM formed alloy after vacuum annealing and hot isostatic pressing treatment was composed of α phase and β phase with the net basket structure morphology. Compared with that under quasi-static condition, the percentage elongation after fracture of the SLM formed alloy at high strain rates was improved significantly. The normalized true stress-true strain curve obtained by simulation was consistent with test results, and the average relative error was 2.5%, indicating the material parameters was recommended for the subsequent transient impact simulation analysis.
  • Reason for Lamellar Cracking of 700 MPa Grade Hot-Rolled High Strength Steel during Shearing Process
    LIU Ying, ZHOU Chaogang, WANG Yunhui
    Materials For Mechanical Engineering. 2020, 44(3): 73-77. https://doi.org/10.11973/jxgccl202003014
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    During shear process, lamellar cracking appeared on the shear section of 700 MPa grade hot-rolled high strength steel plate. The causes of lamellar cracking were analyzed by means of morphology and microstructure observation, chemical composition analysis,micro area composition analysis and tensile property testing. The results show that the serious ferrite-pearlite banded structure caused by composition segregation in the high strength steel was the direct cause of lamellar cracking, and the growth of small holes near the large-sized second phase particles or inclusions in the deformation area at crack tip aggravated the crack growth. By controlling the starting speed and stable casting speed of the continuous caster, adjusting the precision of the roller gap in the sector section, and taking various measures to improve the purity of liquid steel, there was no lamellar cracking in the high strength steel during shear process.
  • Early Fracture Cause of H13 Hot Die Steel Punch
    YU Shijie, CHEN Meng, OUYANG Zhiying
    Materials For Mechanical Engineering. 2020, 44(3): 78-82,86. https://doi.org/10.11973/jxgccl202003015
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    An H13 hot die steel punch fractured during extracting after drilling and forming of drill pipe. The reason for the fracture of the punch was studied by fracture morphology observation, chemical composition analysis, microstructure observation and micro-area composition analysis. The results show that the fracture type of the punch was early fatigue brittle failure. The locations of large inclusions of Al2O3, MnS, VC and defects such as pore and porosity in the outer wall area of the punch work site were easy to produce stress concentration, and became the fatigue crack source. Under cyclic thermal stress, tensile stress, compressive stress and bend load, the lateral microcracks intiated and extended rapidly in divergence form, which eventually led to the fracture of the punch. The content of Mo and V of the punch was far below the lower limit of standard values, resulting in decrease of high temperature mechanical properties of the punch, and then the fatigue fracture of the punch was accelerated.
  • Fracture Cause of Reciprocating Methane Compressor Crankshaft
    MA Xiaoming, WANG Xueting
    Materials For Mechanical Engineering. 2020, 44(3): 83-86. https://doi.org/10.11973/jxgccl202003016
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    The crankshaft of a reciprocating methane compressor ruptured during operation. The fracture cause of the crankshaft was studied by macroscopic and microscopic fracture morphology observation, chemical composition analysis, microstructure observation and mechanical property testing. The results show that the torsional fatigue fracture occurred in the crankshaft. Under the alternating torsonal stresses, the irregular and rough transition fillets of the crankshaft main journal and the rough machining marks near the oil hole produced stress concentration, leading to the initiation of microcracks. The severe banded tempered troostite, non-uniform grains and non-metallic inclusions in the structure caused the poor mechanical properties and accelerated the fatigue crack growth. It was recommended to strictly control the heat treatment and manufacturing process of the crankshaft and optimize the design of the crankshaft structure to prevent similar accidents.
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