25 September 2023, Volume 44 Issue 9
    

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  • LIU Xia-lin, AN Shi-zhong, WANG Bo, REN Feng-zhang
    Transactions of Materials and Heat Treatment. 2023, 44(9): 1-14. https://doi.org/10.13289/j.issn.1009-6264.2023-0089
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    Magnesium-air batteries have attracted much attention in green and clean energy due to their advantages such as low cost, high energy density and high electrochemical equivalence. The research and development of magnesium-air batteries are still greatly hindered, mainly due to the problems of low battery discharge voltage, low anode utilization efficiency and high self corrosion rate in the application process of magnesium alloys. The reasons for these problems lie in the negative difference effect, passivation of discharge products and uneven microstructure of magnesium alloys themselves. Focusing on the anode materials of magnesium-air batteries, the anodic reaction mechanism and existing problems of magnesium alloys are summarized, and then the improvement methods for the electrochemical performance of magnesium alloys are reviewed from three aspects:alloying, processing technology and heat treatment process. Finally, the future development direction of magnesium-air battery anode materials is prospected.
  • TIAN Gao-long, XU Liu-jie, LI Zhou, ZHANG Lian-jie
    Transactions of Materials and Heat Treatment. 2023, 44(9): 15-32. https://doi.org/10.13289/j.issn.1009-6264.2023-0078
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    TZM alloy has the characteristics of high melting point, high strength, low linear expansion coefficient, good corrosion resistance, and good high-temperature mechanical properties.It is one of the most widely used molybdenum alloys and plays an irreplaceable role in many fields.Based on the research status of TZM alloy and on the basis of molybdenum alloy hot working forming and strengthening theory, the preparation methods, mechanical properties control methods, microstructure control methods and the latest research progress of TZM alloy are reviewed in this paper.The control strategies, such as changing doping and sintering processes, and alloy elements and second phases control, are introduced.In addition, the relationship between these interfaces and the properties of TZM alloy is also discussed.Finally, the future research direction and development of TZM alloy are prospected based on the strengthening and toughening mechanism.
  • JIAO Yan-ke, XIONG Yi, YAO Huai, REN Feng-zhang
    Transactions of Materials and Heat Treatment. 2023, 44(9): 33-42. https://doi.org/10.13289/j.issn.1009-6264.2023-0048
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    Effect of solution treatment on microstructure and properties of Mg-2.0Zn-0.4Mn-xAl alloy was studied by means of optical microscope(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and universal material testing machine, and the corrosion resistance of the alloy in 3.5%NaCl solution was studied by static mass loss experiment and electrochemical test. The results show that the number and size of the second phase in the alloy increase with the increase of Al content, and the composition of the second phase changes from the nanoscale rod-like MgZn2 phase and elliptic Mg2(Zn, Al)11 phase(0-4 mass%Al) to Mg17Al12 phase(6 mass%Al).When the content of Al is 4.0 mass%, the alloy has good comprehensive mechanical properties and corrosion resistance, and its ultimate tensile strength, yield strength and elongation are(180.1±3.1) MPa,(124.7±2.8) MPa and(16.7±1.5)%, respectively. After immersion in 3.5% NaCl solution for 72 h, the average static corrosion rate and the hydrogen evolution corrosion rate of the alloy are(0.822±0.056) mm/y and(0.790±0.045) mm/y, respectively.
  • LI Mao-hua, CHEN Zhi-long, XU Yi-wen, LU Li-wei, YANG Yan-qing, SUN Jia-lin
    Transactions of Materials and Heat Treatment. 2023, 44(9): 43-50. https://doi.org/10.13289/j.issn.1009-6264.2023-0047
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    Effect of final aging on microstructure and mechanical properties of 7475 aluminum alloy during two-stage aging treatment was studied by means of transmission electron microscopy and universal material testing machine. The results show that when the first aging process is 120℃×5 h and final aging process is 160℃×14 h, the amount of precipitated phases in the alloy matrix is large, the precipitates are fine and dispersed, the precipitation free zone at the grain boundary is relatively narrow, and the precipitated phases at the grain boundary are discontinuously distributed. At this time, the tensile strength, yield strength and elongation of the alloy are the best, which are 509 MPa, 463 MPa and 12.4%, respectively. Compared with the untreated alloy, the tensile strength, yield strength and elongation increase by 4.5%, 9.2% and 11.7%, respectively. When the final aging temperature is 160℃, with the increase of the final aging time, the strength of the alloy first increases and then decreases, but the change is not significant. When the final aging temperature is greater than or equal to 165℃, the strength of the alloy decreases significantly with the increase of the final aging time, which is due to the significant broadening of the width of the precipitate free zone at the grain boundary and the significant coarsening of the matrix precipitated phase.
  • YU Cong, CHEN Le-ping, ZHOU Quan, YUAN Yuan-ping
    Transactions of Materials and Heat Treatment. 2023, 44(9): 51-60. https://doi.org/10.13289/j.issn.1009-6264.2023-0130
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    7075 aluminum alloy was subjected to T6 aging treatment and electron pulse treatment(EPT) with different current densities(50-125 A/mm2) and different electrification time(480-600 ms).Microstructure and mechanical properties of the alloy after different process treatments were studied by means of scanning electron microscopy, transmission electron microscopy and universal testing machine. The results show that compared to traditional T6 aging treatment, electron pulse treatment with appropriate current density and electrification time can reduce the number and size of precipitates in the alloy, but can increase dislocation density and subgrain quantity. And with the increase of current density and electrification time, the number of second phase resolution and subgrains continuously increases, but the dislocation density first increases and then decreases with the increase of current density, and continuously decreases with the increase of electrification time. The tensile strength and elongation of the alloy first increase and then decrease with the increase of current density and electrification time, and after solution treatment+EPT(470℃×3 h+100 A/mm2×560 ms), the tensile strength and elongation of the alloy reach the highest, which are 555 MPa and 18%, respectively. Compared with T6 aging treatment, the tensile strength decreases by 2.6%, but the elongation increases by 100%. The strengthening mechanism of the alloy after electron pulse treatment is a composite strengthening mechanism of solution strengthening, dislocation strengthening and fine grain strengthening.
  • HE Zhi-rong, ZHANG Wei, ZHANG Kun-gang, DU Yu-qing
    Transactions of Materials and Heat Treatment. 2023, 44(9): 61-68. https://doi.org/10.13289/j.issn.1009-6264.2023-0073
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    In order to develop Ti-Ni based multicomponent shape memory alloys with narrow temperature hysteresis and good shape memory properties, the phase transformation behavior, tensile properties and shape memory behavior of annealed Ti-45Ni-5Cu and Ti-45Ni-5Cu-0.3Cr shape memory alloys were compared and studied by differential scanning calorimeter and tensile test. The results show that the Ti-45Ni-5Cu and Ti-45Ni-5Cu-0.3Cr alloys annealed at 350-700℃ have the same transformation type during cooling and heating, both of which are B2⇆B19'(B2-parent phase, CsCl-type structure; B19'-martensite, monoclinic structure). At room temperature, the tensile curves of the two alloys are similar, showing shape memory effect(SME). With the increase of deformation temperature, SME →SE(superelasticity) transition occurs in both alloys. Compared with the Ti-45Ni-5Cu alloy, the Ti-45Ni-5Cu-0.3Cr alloy has lower martensite transformation temperature, narrower temperature hysteresis, lower tensile strength, higher elongation, higher shape memory platform stress, and lower SME → SE transformation temperature. The Ti-45Ni-5Cu-0.3Cr alloy annealed at 350-700℃ exhibits better SE when deformed at 60℃. The plasticity of the Ti-45Ni-5Cu-0.3Cr alloy annealed at 650℃ is the best, with an elongation of 67.6%.
  • LIN Ying-zheng, YANG Hong-yu, CHEN Fang, YAN Jian-hui
    Transactions of Materials and Heat Treatment. 2023, 44(9): 69-78. https://doi.org/10.13289/j.issn.1009-6264.2023-0062
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    WMoNbCrTi high-entropy alloy is a high temperature structural material with great application potential. The addition of Si is expected to improve its comprehensive mechanical properties. WMoNbCrTiSix(x=0,0.1,0.25 and 0.5) high-entropy alloys were prepared by spark plasma sintering with high-energy ball milling powders as raw materials, and the effect of Si content on its microstructure and mechanical properties was studied. The results show that the microstructure of the high-entropy alloys after adding Si is composed of BCC solid solution, Laves phase and silicide. When x=0.1, Si mainly forms Ti5Si3. When x=0.25, most Si forms Ti5Si3 with Ti, and a few of Si forms Nb3Si with Nb. When x=0.5, Si mainly forms Ti5Si3, Nb3Si and Cr3Si. When x increases from 0 to 0.5, the hardness of the WMoNbCrTiSix high-entropy alloys increases from 9.84 GPa to 13.46 GPa, and the fracture toughness decreases from 6.68 MPa·m1/2 to 4.72 MPa·m1/2. The silicide in the WMoNbCrTiSi high-entropy alloys increases the hardness and reduces the fracture toughness. When x increases from 0 to 0.5, the maximum compressive strain of the alloys increases from 9.1% to 13.2%, and the compressive fracture strength increases from 1758 MPa to 2448 MPa, which is mainly due to the combined effect of grain refinement and silicide.
  • Lü Feng, HUANG Liang, LUO Jun-ming, HUANG You-lin
    Transactions of Materials and Heat Treatment. 2023, 44(9): 79-86. https://doi.org/10.13289/j.issn.1009-6264.2023-0059
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    In order to effectively utilize high abundance rare earths, Ce and La were added to the heavy rare earth diffusion source Dy60Co40 to replace Dy. The effect of different Ce and La additions on properties of Dy60Co40 grain boundary diffusion sintered Nd-Fe-B magnets was studied. The results show that both Dy30Ce30Co40 and Dy30(Ce0.4La0.6)30Co40 grain boundary diffusion can significantly enhance the coercivity of Nd-Fe-B magnets, with values of 1509 and 1527 kA/m, respectively. Compared with the original Nd-Fe-B magnet, the coercivity is increased by 31.7% and 33.2%, respectively, and the decrease in remanence and maximum magnetic energy product is not significant. The microstructure study shows that Ce is mainly distributed in the grain boundary phase to form a Ce-rich phase, which is not conducive to the diffusion of Dy. The addition of La restricts the entry of Ce into the main phase grains, promotes the diffusion of Dy, and further enhances the coercivity of the magnet. The thermal stability study found that the addition of Ce and La can improve the thermal stability of the magnet, but the improvement effect is not as obvious as that of the Dy60Co40 diffusion magnet, which is related to the Ce2Fe14B and La2Fe14B phases that form a low magnetocrystalline anisotropy field.
  • HU Hua-rong, GUO Yuan-jun, YAN Jian-hui, OU Bao-li, CHEN Fang
    Transactions of Materials and Heat Treatment. 2023, 44(9): 87-93. https://doi.org/10.13289/j.issn.1009-6264.2023-0076
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    Mo-12Si-8.5B alloy was prepared by spark plasma sintering method, and the dry friction and wear properties of the Mo-12Si-8.5B alloy paired with SiC were tested at 25-1000℃ using a high-temperature vacuum friction and wear tester. The results show that the temperature has a significant influence on the friction coefficient and wear rate of the Mo-12Si-8.5B/SiC friction pairs, which is related to the combination effect of SiC surface decomposition, graphitization of carbon and oxides generated on the friction pair surface at different temperatures. The friction coefficient of the Mo-12Si-8.5B alloy reaches its minimum value of 0.36 at 600℃, and the wear rate is the minimum at 800℃, which is 0.74×10-6 mm3/(N·m). In addition, the wear mechanism of the Mo-12Si-8.5B alloy is mainly adhesive wear and peeling wear within the range of 25-400℃, while in the high temperature range of 600-1000℃, it is mainly adhesive wear and oxidation wear.
  • ZHANG Jing, ZHAO Zhi-bo, XIN Wen-bin, GU Jing-yuan, LUO Guo-ping, PENG Jun
    Transactions of Materials and Heat Treatment. 2023, 44(9): 94-105. https://doi.org/10.13289/j.issn.1009-6264.2023-0030
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    The dynamic continuous cooling transformation curves of Nb-V-Ti-N microalloyed steel were studied by using Gleeble-3800 thermal-mechanical simulator, and the effect of cooling rate after recrystallization deformation on its microstructure and properties was investigated. The results show that when the cooling rate increases from 0.1℃/s to 30℃/s, the phase transformation of ferrite, pearlite, bainite and martensite occurs in the experimental steel, and the corresponding cooling rate range is 0.1-30℃/s, 0.1-8℃/s, 3-30℃/s and 15-30℃/s, respectively. With the increase of cooling rate, the transformation temperatures of ferrite, pearlite and bainite decrease from 785, 682 and 498℃ to 625, 553 and 415℃, respectively, while the transformation temperature of martensite increases from 342℃ to 365℃. When the cooling rate increases from 3℃/s to 8, 20 and 30℃/s, the proportion of large angle grain boundaries in the steel decreases from 0.734 to 0.509, the average effective grain size first decreases from 10.62 μm to 7.46 μm and then increase to 9.61 μm, and the minimum value is obtained at 20℃/s. The average KAM value first decreases slightly from 0.419° to 0.407° and then increases to 0.691 °, and the minimum value is obtained at 8℃/s. In addition, when the cooling rate increases from 0.1℃/s to 30℃/s, the microhardness of the experimental steel gradually increases from(197±23.3) HV0.1 to(316±11.8) HV0.1, and the yield strength increases from(475±67.1) MPa to(818±33.9) MPa. The analysis shows that in order to obtain a good strength-toughness match, the appropriate cooling rate of the experimental steel after recrystallization deformation is 8℃/s.
  • WANG Xin, WANG Zun-cheng, AI Cheng-shen, MA Liang, CUI Pi-lin, PANG Qi-hang, LI Wen-zhu
    Transactions of Materials and Heat Treatment. 2023, 44(9): 106-113. https://doi.org/10.13289/j.issn.1009-6264.2023-0065
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    Effect of coiling temperature on hot-rolled microstructure evolution and mechanical properties of 12Cr1MoV heat-resistant steel was studied by means of scanning electron microscopy(SEM), transmission electron microscopy(TEM) and universal tensile testing machine. The results show that with the increase of coiling temperature, the tensile strength and yield strength of the experimental steel decrease, while the elongation increases. Only when coiling happens at 660℃, the stress-strain curve of the experimental steel shows continuous yielding, while yield plateau appears at other coiling temperatures. When coiling is carried out at 710℃, the 12Cr1MoV heat-resistant steel has the best comprehensive mechanical properties, with the tensile strength of 689 MPa, the yield strength of 597 MPa and the elongation of 17%. The strengthening and toughening of the experimental steel is the result of a comprehensive effect of various strengthening mechanisms such as fine grain strengthening, phase transformation strengthening and precipitation strengthening. Only an appropriate coiling temperature can simultaneously exert the effects of phase transformation strengthening and precipitation strengthening, ultimately achieving excellent comprehensive mechanical properties of the experimental steel.
  • WU Ying-tong, QIAO Gui-ying, XU Kai, XIAO Fu-ren
    Transactions of Materials and Heat Treatment. 2023, 44(9): 114-121. https://doi.org/10.13289/j.issn.1009-6264.2023-0072
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    Effect of hydrogen on tensile and fatigue properties of ferrite/bainite dual-phase X70 pipeline steel was studied by electrochemical hydrogen charging method. The morphology of tensile and fatigue fracture surfaces and microstructure near the fatigue fracture surface were observed by means of scanning electron microscopy(SEM) and electron backscatter diffraction(EBSD) technique. The results show that the hydrogen has little effect on the strength of the dual-phase X70 pipeline steel, but significantly reduces its plasticity, especially the elongation. After hydrogen charging, the tensile fracture changes from plastic dimple fracture to brittle quasi-cleavage fracture. Hydrogen significantly accelerates the initiation and propagation rate of fatigue cracks in the steel, reducing fatigue life. Hydrogen accelerates the aggregation of dislocations and other defects at grain boundaries and ferrite/bainite interfaces, which leads to the change of fracture mode, thus reducing the plastic and fatigue life of the steel.
  • SUN Ying, HE Lian-fang, GAO Yu-feng, SUN Ran, LI Zhi-chao, LI Hui-ping
    Transactions of Materials and Heat Treatment. 2023, 44(9): 122-129. https://doi.org/10.13289/j.issn.1009-6264.2023-0056
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    Effect of different blanking temperatures(600-800℃) on microstructure, burnish zone width, dimensional accuracy and maximum punching force of BR1500HS boron steel gear-shaped blanking parts were studied by means of optical microscope, scanning electron microscopy and microhardness tester. The results show that when the blanking temperature is 600℃, the room temperature microstructure of the blanking parts is a mixture of ferrite, pearlite and bainite. When the blanking temperature is 650℃, the room temperature microstructure is a mixture of ferrite, bainite and a small amount of martensite. When the blanking temperature is 700-800℃, the room temperature microstructure is complete martensite, and the hardness is relatively high and stable at about 550 HV0.1. Taking into account the dimensional accuracy, cross-sectional quality, maximum punching force and microstructure of the blanking parts, the optimal hot blanking temperature for gear-shaped blanking parts is 800℃. At this time, the microstructure of the blanking parts is complete martensite, with good wear resistance, high strength and hardness. The width of the burnish zone of the blanking parts is the largest, the cross-sectional quality is the best, and the maximum punching force is the smallest, which can meet the technical requirements of the precision gear parts.
  • WANG Sun-zhong, PENG Xing-dong, ZHANG Peng, LIU Lei, XING Yu-jie
    Transactions of Materials and Heat Treatment. 2023, 44(9): 130-139. https://doi.org/10.13289/j.issn.1009-6264.2023-0057
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    Electron backscatter diffraction(EBSD) and scanning electron microscopy(SEM) were used to analyze the texture, recrystallization and fatigue fracture surface of EH36 ship plate steel treated by normalizing process. The fatigue crack propagation behavior, fatigue fracture mechanism and the effect of external load and stress ratio on the stress intensity factor amplitude of the normalized EH36 ship plate steel were studied by means of tensile test, fatigue crack propagation rate test, fatigue fracture toughness test and numerical simulation. The results show that the EH36 ship plate steel has strong {110} and {111} plastic texture components, the average grain size is 8.2 μm, the proportion of deformed grains is 4.1%, and the elongation is 33.3%. The fatigue crack propagation life prediction formulas for stress ratios of 0.03 and 0.1 are obtained through double logarithmic linear fitting, which are da/dN=1.07×10-9K)3.49 and da/dN=1.96×10-9K)3.35, respectively. The fatigue fracture toughness KJ0.2BL(30) of the normalized EH36 ship plate steel is 387 MPa·m1/2 calculated by J-integral method. The fatigue fracture mechanism of the experimental steel is a mixed fracture mechanism of cleavage transgranular fracture and microporous growth polymerization fracture. The multi-parameter simulation shows that under a constant maximum external load, the amplitude of stress intensity factor decreases with the increase of stress ratio under the same fatigue crack length. When the ratio of fatigue crack length to the length of the standard compact tensile specimen is 0.62, it can be used as a criterion for the experimental steel to enter the transient fracture zone.
  • HAN Dong, ZHAN Dong-ping, ZHANG Yang-peng, JIANG Hai-chang, RONG Li-jian
    Transactions of Materials and Heat Treatment. 2023, 44(9): 140-149. https://doi.org/10.13289/j.issn.1009-6264.2023-0049
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    G20CrNi2Mo bearing steel workpieces are prone to form banded structure, reducing their fatigue performance and service life. In order to understand the formation causes and elimination methods of banded structure, the effect of heat preservation process on the composition and structure of the banded structure of the G20CrNi2Mo bearing steel was characterized and analyzed by means of optical microscope(OM), scanning electron microscopy(SEM), electron probe microanalysis(EPMA) and electron backscatter diffraction(EBSD) technique. The results show that the reason for the formation of banded structure in the G20CrNi2Mo bearing steel is due to the segregation of C element. The critical cooling rate required for martensite transformation is increased due to the lack of C in some areas, and then the ferrite band is formed by eutectoid in this area during forging cooling. High temperature and long term holding can promote the diffusion of C element, thereby eliminating banded structure. For the carburizing/nitriding heat treatment process, when the treatment temperature is ≥ 820℃, the banded structure can be completely eliminated. When the treatment temperature is ≤ 820℃, the banded structure can be eliminated in advance by normalizing pretreatment at 940℃ for 3 h, and will no longer appear in the subsequent carburizing/nitriding heat treatment process.
  • FENG Lei, BAO Si-qian, ZHANG Yong-qing, QIAN Xue-hai, CHEN Xue-liang, QIAN Zhen, LI Ming-quan
    Transactions of Materials and Heat Treatment. 2023, 44(9): 150-160. https://doi.org/10.13289/j.issn.1009-6264.2023-0045
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    Effect of deformation temperature and deformation amount on microstructure and mechanical properties of niobium-containing HRB400E microalloyed steel bars was studied by thermal simulation experiment. The results show that when the deformation temperature is 850℃ and the second pass deformation is 35%, the yield strength of the experimental steel is 562.14 MPa, the tensile strength is 645.78 MPa, the elongation is 32%, the average grain size is 8.7 μm, the microstructure is relatively uniform and the comprehensive mechanical properties are the best. This is mainly due to the second phase precipitates of the experimental steel are fine and dispersed under this condition, which can not only play a significant role in precipitation strengthening, but also provide more favorable nucleation points for subsequent ferrite transformation, achieve the purpose of refining grains, and significantly improve the mechanical properties of the experimental steel.
  • ZHOU Lang, ZOU Ai-hua, XIA Tian-cheng, GU Xiao-xiao
    Transactions of Materials and Heat Treatment. 2023, 44(9): 161-168. https://doi.org/10.13289/j.issn.1009-6264.2023-0054
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    A nitrided layer was prepared on the surface of 38CrMoAl steel using liquid-phase plasma infiltration technology in electrolytes with different ammonia concentrations. Microstructure and phase composition of the nitrided layer were observed and analyzed by means of optical microscope(OM), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The corrosion resistance of the nitrided layer was tested using the Parstat2273 electrochemical workstation, and its microhardness and wear resistance were tested. The effect of ammonia concentration on the microstructure and properties of liquid phase plasma nitriding of the 38CrMoAl steel was studied. The results show that with the increase of ammonia concentration, the thickness of the white bright layer in the nitrided layer shows an increasing trend, and the thickness of the diffusion layer with needle-like nitrides and fine carbides, as well as the maximum microhardness value of the nitrided layer, show a first increasing and then decreasing trend. When the ammonia concentration is 60%, the thickness of the nitrided layer reaches 160 μm, the diffusion layer is 112 μm, the highest hardness of the nitrided layer is 1023 HV0.1, which is about 3.5 times that of the substrate. The nitrided layer mainly consists of Fe2N and Fe3N phases, and the wear resistance and corrosion resistance of the nitrided layer are superior to those of the substrate.
  • HUANG Ben-sheng, WU Yan-qiu, CHEN Ling-zhi, WANG Xiao-wei, TANG Jing-li
    Transactions of Materials and Heat Treatment. 2023, 44(9): 169-177. https://doi.org/10.13289/j.issn.1009-6264.2023-0067
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    Nickel-based self-lubricating rare earth composite coating was prepared on the surface of 35CrMo steel by high-frequency induction cladding technology, and it was subjected to solution treatment at different temperatures. The effects of solution treatment at different temperatures on the microstructure, microhardness and wear resistance of the coating were studied by means of optical microscope(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD), Vickers microhardness tester and friction and wear testing machine. The results show that after solution treatment, the elements diffuse fully, the dendritic form gradually becomes single, and the microstructure at the interface mostly changes from columnar dendritic to cellular dendritic. After solution treatment at 850℃, the main phases of the composite coating are γ-(Ni, Fe), Cr(Fe-Ni-Cr), Ni3Fe, TiC, Cr23C6 and CrB phases, the average microhardness is the highest, reaching 867.7 HV0.2, the friction coefficient and wear amount are relatively small, which are reduced by 17.21% and 21.66% respectively compared to the coating before solution treatment, and the relative wear resistance is relatively high, which is 2.46.
  • WANG Lin, WANG Xiao-hui, LIU Zhen-bao, LIU Jian-heng, WANG Ben-chi, ZHOU Xiao-long
    Transactions of Materials and Heat Treatment. 2023, 44(9): 178-187. https://doi.org/10.13289/j.issn.1009-6264.2022-0534
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    In order to obtain the hot processing map of 00Cr12Ni11Mo1Ti2 high-strength stainless steel and optimize its hot working process parameters, a Gleeble-3800 thermal simulation testing machine was used to conduct hot compression tests on the experimental steel at deformation temperature of 850-1150℃ and strain rate of 0.01-10 s-1, and its hot deformation behavior was studied. The constitutive equation of the experimental steel under peak flow stress was constructed, and the energy dissipation diagram was constructed based on the dynamic material model. The plastic instability diagram of the experimental steel was constructed using Prasad and Murthy instability criteria, respectively. The results show that the 00Cr12Ni11Mo1Ti2 steel can also undergo dynamic recrystallization in the deformation range where the energy dissipation rate is lower than 0.3. In the range where the strain rate is 1.0 to 10 s-1 and the deformation temperature is 850 to 1000℃, the experimental steel only undergoes partial dynamic recrystallization accompanied by a large number of local deformation bands, which is more consistent with the plastic instability zone predicted by the Murthy criterion. The experimental steel has the best hot workability in the range of deformation temperature of 1050-1150℃ and strain rate of 0.01-10.0 s-1, and can obtain fine and uniform primary austenite grain structure.
  • LI Yu, XU Wang-hui, XIE Wei-feng, YU Chen, ZHAO Rong-ze
    Transactions of Materials and Heat Treatment. 2023, 44(9): 188-194. https://doi.org/10.13289/j.issn.1009-6264.2023-0060
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    In view of the problems of coarse grain size and poor tensile properties of 304 stainless steel narrow gap TIG(tungsten inert gas welding) welded joint, the ultrasonic vibration head was applied to the test plate, and the ultrasonic vibration was introduced into the TIG welding process to weld it. Microstructure and mechanical properties of the welded joint were studied. The results show that after the introduction of ultrasonic vibration, under the combined effect of thermodynamics and dynamics, the weld penetration increases, the transformation rate of columnar crystal to equiaxed crystal in the weld zone increases, the proportion of equiaxed crystal increases, and the grain is refined. Compared with conventional TIG, the introduction of ultrasonic vibration improves the weld microstructure of the 304 stainless steel narrow gap welded joint, improves its mechanical properties, significantly improves the hardness of the weld zone, close to the base metal, and the tensile strength and yield strength of the welded joint are also higher than that of conventional TIG welded joint, and the elongation is also improved. When the ultrasonic amplitude is 40 μm, the tensile strength of the welded joint is the highest of 674 MPa, the yield strength is 376 MPa, and the elongation is 25%.
  • ZHAO Pei-feng, GU Wei-wen, WANG Nan-nan, SHI Hong-xin, QIU Ran-feng
    Transactions of Materials and Heat Treatment. 2023, 44(9): 195-204. https://doi.org/10.13289/j.issn.1009-6264.2023-0172
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    Due to the influence of intermetallic compounds formed at the welding interface, the performance of resistance spot welding joints between aluminum and magnesium alloys is difficult to meet the requirements of engineering applications. In order to improve the performance of the joint and expand the application of aluminum alloy/magnesium alloy spot welding, resistance element welding of AZ31B magnesium alloy and A6061 aluminum alloy was carried out using magnesium rivets with leg diameters of 4, 6, 8, and 10 mm as element components. The microstructure of the joint interface area was observed using scanning electron microscopy, and the effects of welding current and welding time on the tensile shear load of the joint were studied. The results show that a reactant layer is formed at the interface between the rivet cap/upper plate aluminum alloy, rivet leg/upper plate aluminum alloy, and upper plate aluminum alloy/lower plate magnesium alloy in the joint, mainly composed of Al12Mg17, and its thickness varies with different positions. With the increase of welding current and welding time, the diameter of the nugget in the A6061/AZ61B-REW joint increases, and the tensile shear load shows a trend of first increasing and then decreasing. When using a 10 mm leg diameter rivet and welding at a welding current of 25 kA, welding time of 160 ms, and electrode pressure of 4.8 kN, the shear load of the welded joint reaches the maximum value, which is about 5.19 kN.