Heat Treatment of Metals

Research progress on hardening effect and mechanism during annealing of metals

Wu Hao, Gan Zhanghua, Lao Wenjie, Wu Chuandong, Wang Jiamin, Ni Qian

2021, 46(9): 1-6. doi:10.13251/j.issn.0254-6051.2021.09.001

Abstract ( 62 )

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Softening of metals could be achieved during annealing, generally. However, for several specific metals or alloys, the abnormal phenomenon of annealing hardening occurred. The phenomenon and mechanism of hardening effect during annealing in pure metal, Cu alloy, Ni-W alloy, Zn-Al alloy and Al alloy were summarized. It was noted that the annealing hardening could be detected for the as-cast Al-Sc, Al-Yt and Al-Zr alloys, while cold deformation was necessary for the other types of alloys to obtain the annealing hardening. The mechanisms of annealing hardening were summarized as follows, including solute segregation on grain boundary, grain boundary relaxation, grain boundary nailing of the second phase particles, dislocation source-limited hardening, pinning effect of segregated solute atoms on twin boundary migration or dislocation sliding, annealing twins and strengthening of the second phase nanoparticles, etc.

Research progress of high-entropy alloy coating

Chen Mingxuan, Ma Qiang, Meng Junsheng, Li Chengshuo, Shi Xiaoping

2021, 46(9): 7-14. doi:10.13251/j.issn.0254-6051.2021.09.002

Abstract ( 97 )

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The high-entropy alloy coating has a better prospect than traditional alloys in practical engineering applications. The research progress of high-entropy alloy coatings in recent years was summarized. First, the surface cladding technology for preparing high-entropy alloy coatings is introduced in detail, including laser cladding technology, plasma cladding technology, and argon arc cladding technology, and the advantages and disadvantages of each surface cladding technology were analyzed. Then the structure and performance characteristics of the high-entropy alloy coating were summarized. The composition of the phase in the coating includes: solid solution phase, intermetallic compound, nano-precipitated phase, and amorphous phase. High-entropy alloy coating has a series of excellent properties such as high strength and hardness, excellent wear resistance, good corrosion resistance and high temperature oxidation resistance due to various effects. Further, the effect of surface cladding process parameters on quality, the effect of alloying elements on properties and the effect of heat treatment on phase structure evolution were analyzed. Finally, the application prospects and future research directions of high-entropy alloy coatings were prospected.

Research progress of electrodeposited Ni-Fe alloy coating

Yan Tinglin, Gao Xiaoli, Wang Jiyuan

2021, 46(9): 15-20. doi:10.13251/j.issn.0254-6051.2021.09.003

Abstract ( 77 )

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Mechanisms of abnormal co-deposition of nickel and iron in the preparation of Ni-Fe alloy coating by electrochemical deposition are introduced. The influences of parameters of electrochemical deposition, including current density, main salt type and concentration, additives and other factors, on surface morphology, alloy composition, phase composition and performance of the Ni-Fe alloy coating are reviewed, and the applications of Ni-Fe alloy coating in wear resistance and corrosion resistance, hydrogen evolution electrode and magnetic properties are emphatically introduced. Finally, the existing problems of current Ni-Fe alloy coating are summarized, and the future development trends in this field are prospected.

Effect of prior austenite grain size on martensitic transformation in medium manganese steel

Du Pengju, Wu Di

2021, 46(9): 21-27. doi:10.13251/j.issn.0254-6051.2021.09.004

Abstract ( 61 )

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Effect of prior austenite grain size in medium manganese steel on kinetics of martensitic transformation was studied. The kinetics of martensitic transformation and microstructure evolution were analyzed by combining with SEM, XRD, thermal dilatometer and EBSD results. Different prior austenite grain sizes with (190±15), (36±2), (11±2) and (4.8±2) μm were achieved, respectively, by heating at different austenitizing temperatures. The results show that with the decreasing of prior austenite grain size, the martensite start temperature decrease from 289 ℃ to 250 ℃, while the kinetic of martensitic transformation increase at first then decrease. The kinetics of martensitic transformation is closely related to the number of martensite nucleation cites per unit volume, while the number of martensite nucleation cites are closed to the prior austenite grain size and the martensite lath aspect ratio. When the size of prior austenite grain decreases to 5 μm, the aspect ratio of martensite lath increases, while the increase rate of martensite nucleation cites with undercooling significantly reduces, which results in the decrease of the rate of martensite transformation.

Thermal tensile deformation behavior of Cu-Cr-Zr alloy with different Cr content

Liao Xuefeng, Zhang Heng, He Xueqing, Huang Yuanchun, Li Ming

2021, 46(9): 28-35. doi:10.13251/j.issn.0254-6051.2021.09.005

Abstract ( 53 )

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High-temperature thermal tensile experiments were carried out by using Gleeble-3810 thermal simulation tester to study the flow behavior of Cu-Cr-Zr alloys with different Cr contents at deformation temperature of 350-500 ℃ and strain rate of 0.01-1 s^-1. The results show that with the increase of strain rate, Cr element content and decrease of deformation temperature, the flow stress of Cu-Cr-Zr alloy increases. The analysis of the fracture structure suggests that the strain rate, deformation temperature, and Cr content can change the properties of the material by affecting the formation and morphological changes of dimples and other structures during the thermal tensile process. The increase of Cr content triggers solid solution strengthening and aging precipitation strengthening, which increases the thermal tensile peak stress of the material. Using the experimental results, an improved Johnson-Cook constitutive model is established, and it is found that the calculated results by the model are in good agreement with the experimental data.

Effect of nitrogen and heat treatment on microstructure of 028 alloy

Gong Fangyuan, Feng Hanqiu, Lang Yuping, Chen Haitao, Wang Man, Zhu Xiongming, Leng Chongyan

2021, 46(9): 36-41. doi:10.13251/j.issn.0254-6051.2021.09.006

Abstract ( 52 )

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Influence of main elements of 028 alloy on saturated solubility of nitrogen and precipitation temperature of equilibrium phase was analyzed by using Thermo-Calc software, and the tested alloys with different nitrogen contents were designed. The microstructure of the tested alloys was observed and studied by means of optical microscope and SEM. The results show that Cr, Mo and Mn promote the saturated solubility of nitrogen, Ni and Cu reduce the saturated solubility of nitrogen, Ni reduces the precipitation temperature of σ phase remarkably, but Cr and Mo increase the precipitation temperature of σ phase remarkably. The equiaxial properties of grains become better with the increase of solution temperature, and fully recrystallized equiaxial crystals are obtained at 1080 ℃. When the solution treatment temperature exceed 1110 ℃, the recovery and recrystallization of the tested alloys are complete and the grain grow rapidly. At the same solution treatment temperature, the higher the nitrogen content is, the smaller the grain of the tested alloy is, which indicates that N plays a role in grain refining.

Preparation and tribological properties of W6Mo5Cr4V2/A100 composites

Ji Linlin, Li Changsheng, Sun Jianrong, Gou Zhou, Zhang Hao

2021, 46(9): 42-46. doi:10.13251/j.issn.0254-6051.2021.09.007

Abstract ( 43 )

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In order to improve the tribological properties of A100 steel, pure A100 steel alloy powder and W6Mo5Cr4V2/A100 alloy powder with 10%, 17%, 23%, respectively, tungsten-molybdenum high-speed steel were prepared by gas atomization, then powder metallurgy process was used to prepare W6Mo5Cr4V2 /A100 composites. Effect of W6Mo5Cr4V2 steel content on mechanical properties and tribological properties of the composites was studied, and wear mechanism was discussed. The results show that as the content of W6Mo5Cr4V2 steel increases, the hardness of the composites increases first and then decreases, the friction coefficient and wear rate are reduced to varying degrees, but the density and toughness of the material are slightly reduced. When the content of W6Mo5Cr4V2 steel is 17%, the tribological properties of the composite material are optimal, which is closely related to its excellent microstructure and mechanical properties.

Effect of Zr content on aging precipitation and properties of Al-Zr alloy

Chen Baoan, Zhu Zhixiang, Wang Ruihong, Chen Xin, Han Yu, Li Hongying, Xiao Xiang

2021, 46(9): 47-52. doi:10.13251/j.issn.0254-6051.2021.09.008

Abstract ( 48 )

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Effects of Zr addition (0.05, 0.15 and 0.25wt%) on precipitation, hardness, electrical conductivity of solution-treated and solution-rolled Al-Zr alloys were compared and studied. The results show that the grain size of solution-treated Al-Zr alloys deceases with the increase of Zr content, but the grain size of solution-rolled alloys is insensitive to the Zr addition. Due to the precipitation of Al₃Zr particles in the aging process at 350 ℃, the hardness of solution-treated Al-Zr alloys increases with the increase of Zr content. However, stronger lattice distortion field leads to the decrease of electrical conductivity. During the aging of solution-rolled Al-Zr alloys, a large number of deformation dislocations promote precipitation of the Al₃Zr phase, which makes the Al-Zr alloys aged at 250 ℃ to have better combined properties of hardness and conductivity than that aged at 300 ℃. Especially, with the addition of 0.25wt%Zr in the Al-Zr alloys, the precipitation strengthening during aging can effectively compensate the hardness lowering caused by dislocation annihilation, so that the high hardness of the alloys is maintained. Overall, the optimal combined properties of hardness and conductivity of 47.5 HV0.05 and 55.6%IACS can be obtained by the solution-rolled Al-0.25wt%Zr alloys aged at 250 ℃ for 25 h.

Effect of Nb microalloying on austenite grain growth of 18CrNiMo7-6 steel

Wang Zimin, Yang Zhiqiang, Hu Fangzhong, Wang Kaizhong, Ding Lei

2021, 46(9): 53-57. doi:10.13251/j.issn.0254-6051.2021.09.009

Abstract ( 57 )

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Austenite grain growth behavior of the 18CrNiMo7-6 steels with Nb and without Nb heated at 900-1100 ℃ for 1-8 h was studied, and the mathematical models of the austenite grain growth of the two tested steels were established. The results show that with the increase of heating temperature and holding time, the austenite grain size of the tested steels increases gradually, and that of the 18CrNiMo7-6 steel with Nb is smaller than that without Nb under the same heating condition. By characterizing the grain growth process of the tested steels as inhibited growth stage (900-1000 ℃) and free growth stage (1000-1100 ℃), more suitable grain growth mathematical models are established respectively for the tested steels with Nb and without Nb.

Effect of cold rolling mode and annealing temperature on microstructure and texture evolution of Al-4Cu-0.73Mg alloy

Jiang Yingge, Huang Jiwu, Jiang Fuqing, Xu Chenglong

2021, 46(9): 58-64. doi:10.13251/j.issn.0254-6051.2021.09.010

Abstract ( 57 )

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Effects of parallel rolling (PR), cross rolling (CR) and annealing temperature on microstructure and texture evolution of the Al-4Cu-0.73Mg(wt%) alloy were investigated by means of mechanical properties test, X-ray diffraction(XRD) and electron backscatter diffraction(EBSD). The results show that after annealing at 100-300 ℃ for 1 h, the PR specimens show obvious copper{112}<111>, S{123}<634> and Brass{011}<211> textures, while the CR specimens exhibit strong Brass texture and H{011}<755> texture. When the annealing temperature exceeds 300 ℃, the deformation textures in the PR and CR specimens gradually transform into recrystallization textures along α fiber, which consist of P {011} <001>, L {011} <011>, E {111} < 110> and R {124} <211>. The grain size of PR and CR specimens first increase and then decrease with the increase of annealing temperature, and the largest grain size can be obtained after annealing at 350 ℃ for 1 h, which are about 8.2 μm and 11.5 μm, respectively. Both the PR and CR specimens without annealing show the highest hardness values of ~108 HV, which gradually decrease with the increase of annealing temperature and finally are stable at about 50 HV. Overall, the effect of rolling modes on specimen textures is greater than that on mechanical properties.

Effect of tempering temperature on microstructure and properties of secondary hardening martensitic stainless steel

Deng Biao, Chen Peng, Wang Guodong

2021, 46(9): 65-71. doi:10.13251/j.issn.0254-6051.2021.09.011

Abstract ( 108 )

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Considering that the secondary hardening is very sensitive to the tempering temperature, the evolution of microstructure and properties was systematically studied when a Mo-bearing secondary hardening martensitic stainless steel tempered at 250-650 ℃, and the relationships between the microstructure and the mechanical properties were analyzed by using XRD, SEM, TEM and impact testing. In addition, the mechanisms of the toughening by retained austenite and the secondary hardening for the tested steel were discussed in detail. The results show that when tempered at 480-500 ℃, the phenomena of secondary hardening and temper embrittlement appear simultaneously in the tested steel, so the macrohardness and the impact property are respectively above 56 HRC and about 14 J·cm^-2, with the corresponding microstructure being composed of nanometer-sized alloy carbides, lath martensite and retained austenite. The secondary hardening is attributed to dispersion strengthening of nanometer-sized alloy carbides, and about 10% retained austenite in volume fraction is beneficial to improve the impact property. When the tested steel is tempered at temperatures lower or higher than 480-500 ℃, the impact property is relatively higher, but the macrohardness is lower.

Influence of heat treatment process on microstructure and properties of M2 high speed steel

Li Liangjun, Zhang Jiamin, Chi Hongxiao, Zhou Jian

2021, 46(9): 72-78. doi:10.13251/j.issn.0254-6051.2021.09.012

Abstract ( 86 )

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Effect of heat treatment on microstructure and properties of the M2 high speed steel was studied. The results show that the microstructure of the M2 steel after quenching is quenched martensite+retained austenite+a large amount of carbides. With quenching temperature increasing, the content(mass fraction) of retained austenite in the M2 steel increases, the retained austenite after three times of tempering is basically completely eliminated, while the content of retained austenite after adding subzero treatment is higher than that after three times of tempering, which results in the improvement of strength and toughness of the steel. Comparing the microstructure and properties of the steel under different heat treatment conditions, the best heat treatment process is 850 ℃×30 min preheating+1160 ℃×30 min quenching+(－65 ℃×1 h) subzero treatment+560 ℃×2 h tempering for 3 times.

Effect of finish rolling temperature and annealing temperature on microstructure and properties of 5052 aluminum alloy sheet

Huang Juan, Huang Yuanchun, Shen Zhenyu, Li Xiangyue, Zeng Yu, Yang Gengchen

2021, 46(9): 79-84. doi:10.13251/j.issn.0254-6051.2021.09.013

Abstract ( 76 )

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Effects of finish rolling temperature and annealing temperature on microstructure and properties of the 5052 aluminum alloy sheet were studied by using tensile and hardness tests, microstructure and tensile fracture observation. The results show that, without annealing after rolling the recrystallization occur on the surface layer of the sheet,while only a recovery process occurs in the center layer structure. After annealing, with the increase of annealing temperature, the strength and hardness of the alloy sheet decrease, but the elongation increases. When the final rolling temperature of the 5052 aluminum alloy is not lower than 330 ℃, a uniform microstructure can be obtained during the subsequent cold working, and a more excellent comprehensive properties of 5052-O state alloy sheet can be obtained after annealing at 400-500 ℃, at which the mechanical properties are R_m≥175 MPa,R_p0.2≥65 MPa and A≥32%.

Effect of annealing on grain boundary characteristics distribution and conductivity of copper wire

Zhu Ting, Lu Xianke, Yang Sen

2021, 46(9): 85-89. doi:10.13251/j.issn.0254-6051.2021.09.014

Abstract ( 105 )

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Industrial pure copper wires prepared by the drawing method were annealed under different parameters, and the grain boundary characteristic distribution (GBCD) of the samples before and after annealing was tested by using electron backscatter diffraction (EBSD) technology. The results show that the conductivity and special grain boundary ratio of the copper wire are increased to a certain extent after annealing, and the conductivity increases with the Σ3 grain boundary ratio increasing, while the grain size has no obvious effect on conductivity. When annealed at 550 ℃ for 15 min, the proportion of special grain boundaries reaches the highest value of 57.59%, the proportion of Σ3 grain boundaries reaches the highest value of 49.80%, and the conductivity could reach 59.29%IACS, which is 2.56 times of that before annealing.

Effect of annealing process on microstructure and mechanical properties of 3003 aluminum alloy plate

Li Xiao, Cheng Xiaonong, Xu Guifang, Yang Chengkang, Chen Leli

2021, 46(9): 90-94. doi:10.13251/j.issn.0254-6051.2021.09.015

Abstract ( 346 )

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Effect of annealing process on microstructure and mechanical properties of the 3003 aluminum alloy plate was studied. The results show that the annealed second phase particles is mainly composed of Al₆(Mn, Fe), Al₆Mn and α-Al(Fe, Mn)Si phases formed at defects such as dislocations or subgrain boundaries. With the annealing temperature and holding time increasing, the second phase particles coarsen and grow, and a small number of dispersed second phases appear. When the annealing temperature is 450 ℃, the precipitated phase starts to re-dissolve into the matrix. With the annealing temperature increasing, the hardness is stabilized at about 31.0 HV0.5, and the tensile strength tends to decrease as a whole, while the elongation increases.

Effect of heat treatment on microstructure and hardness of ZCPC-BTMCr20 high chromium cast iron

Ping Zhaofu, Zhou Yi, Zheng Baochao, Tu Xiaohui, Li Wei

2021, 46(9): 95-103. doi:10.13251/j.issn.0254-6051.2021.09.016

Abstract ( 67 )

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A hammerhead for crushing ore produced by factory had a relatively low service life, and it fails due to severe wear only in about 20 h. The influences of different heat treatment processes on hardness and microstructure of the hammerhead were studied. The results show that the composition of the hammerhead specimen is close to that of the ZCPC-BTMCr20 high chromium cast iron, the matrix is a softer pearlite structure, and the macroscopic Rockwell hardness is only 41.1 HRC, which does not meet the requirements of relevant standards. After heating and holding at 960 ℃, 985 ℃, 1010 ℃ respectively, martensite or austenite matrix can be obtained by controlling the cooling rate, and the hardness of the matrix is improved, with the macroscopic hardness greater than 58 HRC. Based on comprehensive analysis for ZCPC-BTMCr20 high chromium cast iron, it is recommended to adopt a heat treatment system of 960 ℃ air quenching+450 ℃ tempering, so the Rockwell hardness can reach 60.1 HRC.

Effect of aging time on microstructure and shear properties of Cu/In-Sn-2.5Ag/Cu solder joint

Qiao Jian, Liu Zheng, Gao Huiming, Yang Li

2021, 46(9): 104-107. doi:10.13251/j.issn.0254-6051.2021.09.017

Abstract ( 55 )

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Microstructure and shear properties of the Cu/In-Sn-2.5Ag/Cu composite solder joint aged at 125 ℃ for different time were studied. The results show that the thickness of intermetallic compounds (IMCs) layer at the interface of the Cu/In-Sn-2.5Ag/Cu solder joint increases with the increase of aging time. Cu₆ (In, Sn)₅ phase is first formed at the interface, and a small number of Ag₉In₄ phases are produced in the solder. Cu₃(In, Sn) phase is generated by the further reaction of Cu atoms with the solder, and a part of Ag₉In₄ phase transforms into Ag₃In phase with the increase of aging time. The solder joint full of IMCs is formed when the aging time extends to 168 h. The shear strength of the solder joint increases first and then decreases with the increase of aging time. The shear strength reaches a maximum of 15.38 MPa when the aging time is 120 h.

Effect of annealing process on microstructure and properties of Al-Zr-Er high conductivity aluminum alloy

Zhou Zeyu, Xiao Xiang, Zheng Zhikai, Chen Baoan, Xu Jing, Xia Feifei

2021, 46(9): 108-115. doi:10.13251/j.issn.0254-6051.2021.09.018

Abstract ( 72 )

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Effect of annealing process on microstructure and properties of the Al-Zr-Er alloy prepared by water-cooled copper mold was studied by means of hardness tester, electrical conductivity gauge and scanning electron microscope. The results show that when the addition amount of Er increases from 0 to 0.30wt%, the primary Al (Fe,Er) phase in the Al-Zr-Er alloy increases gradually, and a large number of nano-sized Al₃ (Zr,Er) particles are precipitated during annealing. During the isochronous annealing process of Al-Zr-Er alloy, hardness and electrical conductivity exist two peak positions. The first peak is at 300-400 ℃ which represents the precipitation process of Al₃Er and the second peak is Al₃(Zr, Er) at 500-550 ℃ .In the annealing process, multi-stage annealing can more fully form Al₃ (Zr, Er) particles of core-shell structure, and the hardness is improved significantly. During the three-stage annealing process, Zr and Er elements in the matrix are more fully precipitated, and the conductivity is the highest. In terms of composition, the addition of 0.15wt%Er in the Al-0.10Zr-xEr alloy shows better comprehensive properties. Although adding Zr element to Al-yZr-0.15Er alloy will increase the hardness of the alloy, the insufficient precipitation of Zr element will lead to the loss of electrical conductivity.

Heat treatment of TB8 titanium alloy with high strength and toughness

Li Minna, Ma Baofei, Guo Jinming, Wu Chen, Xiao Songtao

2021, 46(9): 116-119. doi:10.13251/j.issn.0254-6051.2021.09.019

Abstract ( 86 )

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Effects of solution treatment and aging process on microstructure and properties of TB8 titanium alloy bars were studied. The results show that single equiaxed β grain of the alloy is obtained after 890 ℃ solution treatment. With solution time increasing, the strength reduces gradually. After aging at 520 ℃ for different time, a large number of secondary α phases are precipitated in β grains, which increases the aging strength of the bar. When aging for 8 h, the strength of the alloy reaches 1286 MPa and good plasticity is retained. The recommended solution treatment and aging system of the TB8 titanium alloy bar is 890 ℃×30 min, WQ+520 ℃×8 h, AC.

Influence of aging treatment on microstructure and properties of 7A55 aluminum alloy

Ding Xuan, Gan Yurong, Jiang Aijuan, Li Hui, Yang Mingqiu

2021, 46(9): 120-123. doi:10.13251/j.issn.0254-6051.2021.09.020

Abstract ( 60 )

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Influence of aging treatment on microstructure evolution and properties of 7A55 aluminum alloy was investigated. The microhardness, mechanical properties and electrochemical corrosion behavior were tested. The TEM microstructure and corrosion morphology were characterized. The results indicate that the experimental 7A55 aluminum alloy after solution treatment has higher hardening rate. After aging at 160 ℃ for 12 h, the hardness reaches the peak (87 HV0.5) from 56 HV0.5 in the solution treated state, i.e., increased by 55.36%, and the hardening rate in early aging stage is very high. Pre-aging (PA) treatment inhibits the natural aging (NA) effect and improves the bake hardening (BH) response. The yield strength under PA+NA state after BH treatment reaches 475 MPa with an increment of 190 MPa, which improves 66.67%, and the elongation reaches 12.5%. The precipitated particles under PA+NA+BH state are finer and uniformly distributed, with the diameter in the range of 10-15 nm. The PA+NA+BH state alloy has the highest corrosion potential (－1.032 V, vs SCE), the least corrosion pits and the best corrosion resistance, with the average corrosion depth being about 33 μm.

Effect of multi-stage solid solution treatment on microstructure and properties of 7136-0.35La aluminum alloy

Wang Chunhua,Wang Feng , Wang Fengliang, Fang Hongjie, Yang Lijuan

2021, 46(9): 124-128. doi:10.13251/j.issn.0254-6051.2021.09.021

Abstract ( 53 )

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7136-0.35La aluminum alloy was subjected to solid solution treatment in single-, double-, and three-stage respectively and then single-stage aging, and the solid-solution metallography, tensile fracture morphology and energy spectra, alloy hardness, fracture properties, and electrochemical parameters were tested by scanning electron microscope, hardness tester, universal tensile tester, electrochemical workstation and other equipment. The results show that the re-dissolution effect for three-stage treated solid solution microstructure is better, and the number of corrosion cracking sources is preliminarily reduced. The elongation of the three-stage solution treated then aged alloy is 13.65%, which is 21.9% higher than that single-stage treated, and with ductile fracture as the primary fracture mode. However, the three aged alloys solid-solution treated in single-, double- and three-stages show similar resistance to electrochemical corrosion, so the single stage solution treatment is preferred when taking the corrosion property as the main criteria.

Influence of intermediate annealing on microstructure and properties of cold rolled AlMgSiCu aluminum alloy sheet

Gong Hao, Kong Debin, Guo Lina, Han Hongwen, Gong Jingjing, Fang Hongjie

2021, 46(9): 129-132. doi:10.13251/j.issn.0254-6051.2021.09.022

Abstract ( 73 )

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Influence of intermediate annealing on microstructure and mechanical properties of the cold rolled AlMgSiCu aluminum alloy sheet was studied by using tensile testing machine, TEM and XRD. The results indicate that the strength has no obvious change after 300 ℃×2 h and 400 ℃×2 h intermediate annealing. The n and r values increase with intermediate annealing temperature increasing, which arrives respectively 0.286 and 0.623 after annealing at 400 ℃ for 2 h, and recrystallization occurs and most grains are equiaxed after 400 ℃×2 h intermediate annealing. Three types of secondary phases are in the matrix: AlFeMnSi particles of about 1 μm in size, long rod AlMgSiCu phases of 0.1 μm in width and globular Si particles. The long rod AlMgSiCu phase first precipitates and then re-dissolves with the increase of intermediate temperature. The volume fraction of Brass{011}<211> texture and S{123}<634> texture of the alloy without intermediate annealing is the highest, and reaches 13.9% and 25.7%, respectively. After 400 ℃×2 h intermediate annealing, the texture in the specimen is mainly 24.3% of Cube{001}<100> type, with 10.5% of r-Cube type (both in volume fraction).

Effect of quenching temperature on microstructure and mechanical properties of a medium alloy martensitic wear-resistant cast steel

Yu Hongjun, Chen Zhengjia, Chi Xiaoming, Pei Zhongzheng, Cheng Fuchao, Xu Jie, Wang Yongjin

2021, 46(9): 133-137. doi:10.13251/j.issn.0254-6051.2021.09.023

Abstract ( 77 )

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A self-designed medium alloy martensitic wear-resistant cast steel was quenched at 900, 950, 1000, 1050, 1100 ℃ then tempered respectively, and the influence of quenching temperature on microstructure and mechanical properties of the tested steel was studied. The results indicate that the microstructure of the tested steel after quenching and tempering is composed of lath martensite and retained austenite. When the tempering temperature is kept constant at 250 ℃, with the increase of quenching temperature, the martensite structure first becomes finer and then coarser, and the tensile strength, impact properties and residual austenite content increase first and then decrease. The tested steel achieves the best comprehensive mechanical properties at 1050 ℃: tensile strength of 1623 MPa, impact property value of 14.4 J, the corresponding strengthening mechanism is twin martensite and high-density dislocation entanglement. And the wear behavior and the wear mechanism of the tested steel under this process are explained by the impact wear test.

Effect of stabilization treatment on mechanical properties and dimensional stability of DC53 steel

Qiu Huaxing, Wu Zhenghuan, Li Xiaohui, Gu Liwen, Huang Lifeng

2021, 46(9): 138-141. doi:10.13251/j.issn.0254-6051.2021.09.024

Abstract ( 57 )

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Effects of conventional heat treatment and stabilization treatment after tempering on mechanical properties and dimensional stability of the cold work mold steel DC53 were investigated by using scanning electron microscope (SEM), X-ray diffraction(XRD), hardness, toughness and coordinate measuring machine (CMM). The results show that the microstructure of the DC53 steel consists of tempered martensite, a small amount of retained austenite and carbide before and after the stabilization treatment. After the stabilization treatment with additional tempering at 400 ℃ for 2 h, the hardness and impact absorbed energy of the tested steel are 61.5 HRC and 19.7 J, respectively, while the dimensional stability of the material is further improved. The improvement of microstructure stability after tempering, the reduction of the residual stress values in the material and the aging of retained austenite are the main reasons for the improvement of dimensional stability of the tested steel.

Effect of normalizing rolling and subsequent normalizing process on microstructure and properties of S460NL high-strength low-temperature structural steel

Pan Zhongde, Zhang Pengcheng, Wu Huibin, Hu Qilong

2021, 46(9): 142-145. doi:10.13251/j.issn.0254-6051.2021.09.025

Abstract ( 54 )

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Based on EN10025-3 standard, the chemical composition of the normalized high-strength low-temperature structural steel S460NL was designed with medium carbon, low phosphorus, sulfur, nitrogen and hydrogen; then through high-homogeneous smelting and continuous casting process, the steel plates with different specifications were produced respectively by normalizing rolling and by normalizing rolling+normalizing. The results show that the steel plates by normalizing rolling process can meet the performance requirements of EN10025-3 standard and EN10164 Z35 standard for the S460NL steel plates with specifications below 60 mm, while for that 60 mm and above, additional normalizing process is required to meet such performance requirements. The normalizing-rolled+normalized S460NL steel plates have excellent tensile properties and excellent impact properties at －50 ℃ after PWHT simulated post welding heat treatment, which meets the standard requirements.

Effect of heat treatment on microstructure and properties of Ti80 titanium alloy bars

Hua Yao

2021, 46(9): 146-148. doi:10.13251/j.issn.0254-6051.2021.09.026

Abstract ( 77 )

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Effects of different heat treatment process on microstructure and room temperature mechanical properties of the Ti80 titanium alloy bars were studied. The results show that with the increase of heat treatment temperature, the microstructure of the Ti80 titanium alloy changes from equiaxed structure to widmanstatite structure. When plastic forming is required in the later period, it is appropriate to choose the heat treatment process of air-cooling after heating at 850 ℃ for 80 min. After the heat treatment process of heating at 750 ℃ for 80 min and then air-cooling, the strength and plasticity of the Ti80 titanium alloy bars match well.

Effect of thermal process on microstructure and mechanical properties of IC21 single crystal alloy

Shi Guomei, Peng Xin, Li Shusuo, Liu Yong, Zhao Haigen, Liu Jing

2021, 46(9): 149-152. doi:10.13251/j.issn.0254-6051.2021.09.027

Abstract ( 46 )

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Microstructure of the IC21 single crystal alloy at as-cast state, after heat treatment and after different thermal processes were observed by optical microscope(OM) and scanning electron microscopy(SEM).The high-temperature tensile and enduring properties of the alloy at as-cast, heat treated and various thermal processes treated state were tested. The effects of heat treatment and thermal process on microstructure evolution and mechanical properties of the IC21 alloy were studied. The results show that the as-cast alloy is dendritic growth and consisted of γ′ phase, γ phase, bulky γ′ in the interdendritic regions and NiMo phase. The size of γ′ phase in the dendrite region is larger than that in the interdendritic region. The alloy is not complete solid solution after 1315 ℃/6 h/argon cooling and two aging treatment, and the γ′ phase in the dendrite is not completely dissolved. There are still coarse γ′ phases between dendrites. The high temperature rupture properties of the alloy are obviously improved. The γ′ phase grows up obviously and the cubic degree decreases slightly after thermal process. After thermal process, the size difference of γ′ phase between dendrites and interdendrites decreases, and needle phase precipitates. Compared with the heat treatment state, the endurance life of the alloy is slightly reduced, but the tensile strength is improved.

Gas nitriding process for 32Cr3MoVE steel

Wang Huibin, Qiu Rongchun, Chen Kui, Liu Xiangning, Hu Linsen, Hu Yunbo, Huang Junqiong

2021, 46(9): 153-158. doi:10.13251/j.issn.0254-6051.2021.09.028

Abstract ( 63 )

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In order to improve its hardness and wear resistance, the nitriding process was studied for the 32Cr3MoVE steel workpiece. The results show that the lower nitriding temperature and the lower nitrogen potential adopted in nitriding process can effectively control the depth of bright white layer, and avoid the production of coarse alloy nitrides, but the nitriding rate is slower. By keeping the nitrogen potential maintaining always around its threshold through certain multi-stage control mode, the nitriding process can ensure the nitriding rate, control the depth of bright white layer, and inhibit the formation of brittle phases as well. Finally, the suitable gas nitriding process by nitrogen potential threshold control for 32Cr3MoVE steel is obtained through process test validation.

Effect of pulsed magnetic field treatment on properties and microstructure of 7075 aluminum alloy

Shi Yazhou, Lu Guangping, Gao Yi, Liao Chengzhi, Yang Yi

2021, 46(9): 159-163. doi:10.13251/j.issn.0254-6051.2021.09.029

Abstract ( 75 )

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The 7075 aluminum alloy was treated by pulsed magnetic field, and the mechanical properties and microstructure of the alloy before and after pulsed magnetic field treatment were studied by using room temperature tensile test, SEM, TEM and XRD testing methods. The results show that pulsed magnetic fields with peak intensity of 2 T and 3 T can increase the microscopic strain of the alloy and promote the transformation of the preferred orientation of grains from (200) crystal planes to (111) crystal planes, but it does not significantly affect the tensile properties of the alloy. A pulsed magnetic field with a peak intensity of 1 T can significantly promote the re-dissolution of the small-sized second phase inside the alloy, weaken the continuity of the grain boundary precipitation phase, and broaden the width of the grain boundary precipitation-free zone, so that the plasticity of the 7075 aluminum alloy can be improved without reducing the strength.

Effect of heat treatment temperature on microstructure and properties of cold deformed Inconel625 alloy pipe

Qin Xingwen, Wang Kun, Nai Qiliang, Du Lei

2021, 46(9): 164-169. doi:10.13251/j.issn.0254-6051.2021.09.030

Abstract ( 51 )

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Effect of heat treatment temperature on microstructure, mechanical properties and corrosion properties of the Inconel625 stainless steel pipe was studied through metallographic analysis, tensile experiment, hardness experiment and nitric acid corrosion experiment. The results show that the microstructure of the alloy is basically equiaxed grains after heat treatment. With the increase of temperature, the growth rate of grain size shows a trend of slow first and then fast. And the activation energy for grain growth is 144.14 kJ/mol. The tensile strength and hardness of the Inconel625 alloy pipe decrease with the increase of heat treatment temperature. And in the temperature range between 960-1160 ℃, the relationship between tensile strength, hardness and grain size abides by the Hall-Pecth relationship. With the increase of temperature, the fracture mode of the Inconel625 alloy changes from cleavage fracture to ductile fracture; and the rate of intergranular corrosion shows a trend that first decreases and then stabilizes. When the temperature is about 1080 ℃, the curves of hardness and elongation intersects, and the rate of intergranular corrosion are stable , which is the best heat treatment temperature.

Application of ultrasonic cleaning in mesh belt furnace

Liu Yi, Shang Zhaohua, Fu Hongju, Wang Yongqiang

2021, 46(9): 170-172. doi:10.13251/j.issn.0254-6051.2021.09.031

Abstract ( 75 )

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Metal parts needed to be clean before carburizing, but the front cleaning effect of the existing mesh belt furnace was not satisfied. In order to improve the decontamination effect of cleaning in front of the mesh belt furnace, the ultrasonic cleaning device was installed in the furnace. According to the possible space and the characteristics of ultrasonic cleaning, the power, frequency and installation method of ultrasonic cleaning were designed. The results show that after adding an ultrasonic cleaning device, the cleaning effect of the parts is improved, and the infiltrated layer depth of carburized parts is more uniform.

Behavior of γ′ precipitates under high temperature creep of GH4096 superalloy with different solution treatment cooling rates

Lu Yuhua, Wang Haizhou, Fu Rui, Li Fulin, Li Dongling, Huang Danqi, Cai Wenyi

2021, 46(9): 173-179. doi:10.13251/j.issn.0254-6051.2021.09.032

Abstract ( 104 )

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Precipitation-strengthened solution treated GH4096 superalloy was cooled by five different cooling methods. Standard size turbine disc baffles under five cooling rates were prepared separately. The specimens were subjected to high temperature creep tests at 700 ℃ and 690 MPa, and the performance of the five GH4096 superalloy disc baffles was compared. By introducing a novel in-situ statistical characterization method, the in-situ observation and statistical quantitative distribution observation of the strengthening phase in the alloy material-primary, secondary, and tertiary γ′ phases were realized across scales in the form of images. The changes of γ′ phase morphology and size distribution in the materials before and after high temperature creep were compared and discussed. The results show that the GH4096 superalloys obtained by the five cooling rates all exhibit good high-temperature creep properties. The γ′ phase distribution density of the materials under the five processes is 210-260 μm^-2. After the high temperature creep test, the number of γ′ phases is significantly reduced, and the γ′ phase distribution density drops to 150-200 μm^-2. Among them, the decrease of γ′ phase density is mainly due to the decrease of γ′ phases with a diameter less than 36 nm.

Hot compression deformation behavior of Cu-0.5Cr-0.1Zr alloy

Guo Liping, He Xueqing, Yang Daijun, Huang Yuanchun, Wang Qiang

2021, 46(9): 180-186. doi:10.13251/j.issn.0254-6051.2021.09.033

Abstract ( 51 )

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Hot deformation behavior of the Cu-0.5Cr-0.1Zr alloy at 600-750 ℃/0.001-1.0 s^-1 was studied by hot compression test. The results show that the high temperature flow stress, dynamic recrystallization critical values and dynamic recrystallization softening behavior of the Cu-0.5Cr-0.1Zr alloy were closely related to the deformation temperature and strain rate. The thermal activation energy Q and Zener-Hollomon parameter of the Cu-0.5Cr-0.1Zr alloy were calculated using the Arrhenius equation, which are 244.94 kJ/mol and Z=ε·exp(244.94×10³/RT), respectively. Also, the calculated results of the critical values of dynamic recrystallization by using three methods prove that the Poliak-Jonas criterion has the highest accuracy, and based on which the constitutive equation for the critical values of dynamic recrystallization was established. Furthermore, using the net softening effect η values of dynamic recrystallization, the softening behavior of dynamic recrystallization during hot deformation is discussed. Finally, the processing map of the Cu-0.5Cr-0.1Zr alloy is established, from which the best thermal processing parameter is determined to be 680-750 ℃ and 0.03-0.001 s^-1, and the relationship between power dissipation coefficient and dynamic recrystallized grain size is introduced in detail.

Microstructure evolution of a high alloying Al-9Zn-2Mg-2Cu-0.3Ce alloy during homogenization

Zhang Qian, Shi Dandan, Li Caiqiong, Zhao Zhiguo, Shi Xianli

2021, 46(9): 187-192. doi:10.13251/j.issn.0254-6051.2021.09.034

Abstract ( 43 )

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As-cast microstructure and microstructure evolution during homogenization of highly alloying Al-9Zn-2.0Mg-2Cu-0.3Ce alloy were studied by means of optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD) and differential scanning calorimeter (DSC), and a rather optimal single-stage homogenization process was obtained. The results show that in the as-cast alloy, the dendrite network is well developed with serious segregations of Zn, Mg and Cu, and the main non-equilibrium solidification phases are T(AlZnMgCu) phase and θ(Al₂Cu) phase. After homogenization heat treatment at 470 ℃ for 48 h, the dendrite network in the alloy is basically eliminated and the solidification phase T gradually dissolves into the matrix. The main residual phases are high temperature resistant phases Al₂CuMg, Al₈Cu₄Ce and Al₇Cu₂Fe. Diffusion kinetic analysis shows that the single-stage homogenization process of annealing at 470 ℃ for 48 h is sufficient to make the non-equilibrium phase in the alloy to re-dissolve into the matrix.

Heat treatment process of 75Cr1 steel for saw blade substrate and its microstructure and mechanical properties

Dong Shaoming, Hu Jianwen, Liang Ziyu

2021, 46(9): 193-198. doi:10.13251/j.issn.0254-6051.2021.09.035

Abstract ( 232 )

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Microstructure, grain sizes, carbide distribution and mechanical properties of the 75Cr1 steel for saw blade substrate under different heat treatment processes were studied. The results show that microstructures are fine acicular martensite and a less amount of residual austenite after quenching between 780 ℃ and 840 ℃, and the hardness increases slightly with the increase of quenching temperature around the level of 63 HRC. The grain size decreases from grade 10 to grade 8, and unevenness of grains is greater with the increase of temperature. With the increase of tempering temperature, the microstructure changes from tempered troostite to tempered sorbite, and the amounts of granular carbides increase. Quenched at 800 ℃ and tempered at 540 ℃, the microstructure of tempered sorbite with a dispersed distribution of fine carbides is obtained. The hardness of the 75Cr1 steel is 36.5 HRC, with good matching of strength and toughness.

Effect of simulative burn temperature on microstructure and properties of TC4-DT titanium alloy

Hou Jinrui, Zhang Shuang, Zhang Yi, Zhang Lingfeng

2021, 46(9): 199-204. doi:10.13251/j.issn.0254-6051.2021.09.036

Abstract ( 59 )

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The changes of microstructure, strength, hardness and sheet resistance of TC4-DT titanium alloy after burned at four simulative temperatures (850, 950, 1050 and 1150 ℃) were studied by using optical microscope (OM), transmission electron microscope (TEM), microhardness tester and universal tensile testing machine, and a rapid method for burn detection was given. The results show that when the simulative burn temperature is 850 ℃, the alloy equiaxed structure is composed of α phase and a small amount of β phase, and the equiaxed structure will be coarsened with the increase of temperature to 950 ℃. When the simulative burn temperature is 1050 ℃, the grain size increases remarkably and the structure gradually becomes lamellar, with the decrease of primary α phase, the increase of β phase and the precipitation of secondary α phase. With the change of simulative burn temperature to 1150 ℃, the lamella structure will continue to be coarsened. The degree of burn is related to the resistance, strength and hardness of the alloy. With the increase of simulative burn temperature, the sheet resistance increases monotonously, the strength decreases, and the hardness first decreases and then increases. Therefore, the burn degree of titanium alloy can be determined by measuring the sheet resistance.

Effect of reversed austenite stability on strength and toughness of medium-Mn steel

Qi Xiangyu, Yan Ling, Li Guanglong, Li Wenbin, Du Linxiu

2021, 46(9): 205-210. doi:10.13251/j.issn.0254-6051.2021.09.037

Abstract ( 55 )

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A quenched medium manganese steel was tempered, and the content and stability of reversed austenite at different tempering temperatures with its effect on the strength and toughness were studied. The results show that with the tempering temperature increasing from 630 ℃ to 670 ℃, the volume fraction of reversed austenite is increased from 19% to 42%, while its stability decrease constantly; and the yield strength decreases from 750 MPa to 565 MPa, the tensile strength increases from 845 MPa to 970 MPa, the impact toughness at -60 ℃ decreases from 116 J to 75 J. The large volume fraction of reversed austenite with poor stability reduces the yield strength of the steel, but improves the work-hardening ability significantly. The transformation-induced plasticity effect of reversed austenite can increase the crack initiation and propagation energy effectively under impact loading, which is the main toughening mechanism of the medium manganese steel.

Cause analysis of r value decreasing of low carbon aluminum-killed steel sheet developed based on ferrite rolling process

Meng Yuerui, Zhao Xianping, Zhou Bowen

2021, 46(9): 211-215. doi:10.13251/j.issn.0254-6051.2021.09.038

Abstract ( 52 )

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A steel plant tried to develop an SPCC sheet based on ferritic rolling process, cold rolling and bell annealing. It was found that compared with the traditional austenite rolling process, the mechanical properties of the products under this process route were decreased in varying degrees, and the r value was significantly reduced. Then the microstructure and textures of hot rolled sheet and cold rolled annealed sheet with these two processing routes were compared and analyzed, and the improvement measures were put forward. The results show that in the ferrite rolling process, the hot rolling finishing temperature is too high to form two-phase zone rolling, resulting in the uneven room temperature microstructure of coarse F+fibrous F, so that resulting in the existence of high strength {001} <110> texture components in the cold rolled annealed sheet, which is the main reason for the reduction of r value of the final product.

Preparation and thermal stability of AlCrTaTiZrV-nitride diffusion barrier layer

Li Rongbin, Li Ke, Jiang Chunxia, Zhang Rulin

2021, 46(9): 216-222. doi:10.13251/j.issn.0254-6051.2021.09.039

Abstract ( 58 )

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The work aimed to study the effect of different nitrogen flow rates on the properties of AlCrTaTiZrV high-entropy alloy nitride films and to examine the thermal stability of (AlCrTaTiZrV)N diffusion barrier layer with a thickness of 15 nm under the optimum nitrogen content. The (AlCrTaTiZrV)N high-entropy alloy nitride films were synthesized by reactive magnetron sputtering under different nitrogen flow. A 15 nm amorphous AlCrTaTiZrVN₁₀ film was prepared on single crystal silicon as a single-layer barrier material for Cu interconnection. A 50 nm-thick Cu film was deposited on the surface of the AlCrTaTiZrVN₁₀ film to obtain the Si/AlCrTaTiZrVN₁₀/Cu film system. To assess its thermal stability, Si/AlCrTaTiZrVN₁₀/Cu structure was annealed at 500 ℃ in high vacuum for various time to simulate real working conditions. The surface morphology, roughness, phase composition and sheet resistance of the specimens were characterized by means of the field emission scanning electron microscopy (FE-SEM), atomic force microscope (AFM), X-ray diffractometer (XRD) and four-point probe (FPP), respectively. The results show that the AlCrTaTiZrV high-entropy alloy thin film is amorphous structure when the nitrogen flow rate is less than 10%. When the nitrogen content is 20%, the high-entropy alloy nitride film presents FCC structure and the crystallinity of the film is improved with the increase of nitrogen content. When the nitrogen flow rate is 10%, the roughness is the lowest of only 0.124 nm. After annealed at 500 ℃ for 8 h, the grain size increases significantly. However, the sheet resistance of the films remain at a low value of 0.070 Ω/□, and no Cu-Si compound is formed. The amorphous structure of 15 nm AlCrTaTiZrVN₁₀ high-entropy alloy nitride film can effectively prevent the diffusion of Cu after annealing at 500 ℃ for 8 h, showing excellent thermal stability and good diffusion barrier properties on Cu.

Microstructure and wear resistance of laser clad Ni/Ni-WC gradient coating on Cr12MoV steel

Li Li, Ye Hong, Liu Yue, She Hongyan, Qu Wei, Shen Dachen, Chen Li

2021, 46(9): 223-228. doi:10.13251/j.issn.0254-6051.2021.09.040

Abstract ( 77 )

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Ni/Ni-WC gradient coating was clad on the surface of the Cr12MoV die steel by using pulsed Nd:YAG laser, and the phase composition, wear resistance and wear morphology of the gradient coating were studied by X-ray diffractometer, scanning electron microscope and energy spectrometer, high-speed reciprocating friction and wear tester, and white light interferometer. The results show that the Ni60A+35%WC wear-resistant layer are mainly composed of γ-(Ni, Fe) solid solution, WSi₂ phase and many kinds of carbides or hard phases. There are no defects such as cracks and pores between the gradient coating layers and between the coating and the substrate, showing good metallurgical bonding at the interfaces. The average microhardness of the Ni60A+35%WC wear-resistant layer of the gradient coating is about 1.7 times that of the substrate, and the wear mechanism of the Ni/Ni-WC wear-resistant coating is mainly fatigue wear and abrasive wear, while that of the substrate is mainly adhesive wear and abrasive wear.

Effect of overlap rate on microstructure and properties of Ni60A clad coating on TC4 titanium alloy

Gong Yuling, Wu Meiping, Cui Chen, Miao Xiaojin

2021, 46(9): 229-233. doi:10.13251/j.issn.0254-6051.2021.09.041

Abstract ( 57 )

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Multi-pass Ni60A laser clad coating was prepared on the surface of TC4 titanium alloy by using laser cladding coaxial powder feeding technology. The microstructure and properties of the clad coating with overlap rates (30%, 40%, 50%, 60% and 70%) were analyzed by using SEM, hardness test, and friction and wear test. The results show that the overlap rate has a greater impact on the microstructure and properties of the clad coating, which can realize the secondary heating of the coating. When the overlap rate is 50%, the size of hard phase TiC and the content of TiNi in the coating increase, which can effectively improve the hardness of the coating, resist the shear force on the grinding ball, so that the surface is not easy to be damaged, and the surface of the coating is smooth, which can greatly reduce the friction coefficient. When the overlap rate is 30%, the grains can't fully absorb the laser energy, resulting in smaller grain size. But when the overlap rate is too high, the B, C, Ni and other elements in the coating will be diluted with the over burning, resulting in the loss of reinforcing elements in the coating and reducing the mechanical properties of the coating. Therefore, the most suitable overlap rate of the Ni60A coating is 50%.

Effect of adding CeO₂ on properties of Al-Ti laser clad coating on aluminum alloy

Miao Xiaojin, Xia Sihai,Wu Meiping, Yu Jinghu, Zhao Zishuo, Cui Chen, Zhang Chunlei

2021, 46(9): 234-240. doi:10.13251/j.issn.0254-6051.2021.09.042

Abstract ( 74 )

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Effect of adding of rare earth oxide CeO₂ on properties of Al-Ti coating on aluminum alloy by laser cladding was studied. Firstly, the effects of lap ratio on microstructure, microhardness and wear resistance of the coatings were analyzed. Then, the effects of CeO₂ on the properties of the coatings were studied under the condition of 40% lap ratio. The results show that the properties of the coating are the best when the lap ratio is 40%.The microhardness is 284.82 HV0.3, which is 106% higher than that of the substrate; the friction coefficient is 0.440, which is 32% lower than that of the substrate; the wear rate is reduced to 0.0105 mm³·N^-1·m^-1.The grain size is refined and the microhardness and wear resistance of the coating are greatly improved by adding CeO₂. When the content of CeO₂ is 8%, the overall properties of the coating is the best. The microhardness is 305.58 HV0.3, which is increased by 7.3% than that without CeO₂; the friction coefficient is almost the same as before, but the wear rate is only 0.0087 mm³·N^-1·m^-1, which is 17% lower than that without CeO₂.

Superhydrophobic surface of aluminum alloy prepared by anodic oxidation and its corrosion resistance

Zhuang Mingta, Xu Ruisi, Liu Cansen, Jie Xiaohua

2021, 46(9): 241-246. doi:10.13251/j.issn.0254-6051.2021.09.043

Abstract ( 52 )

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Surface morphology, chemical composition and corrosion resistance of the anodized and low surface energy materials modified 7075 aluminum alloy were characterized by contact angle measurement instrument, scanning electron microscopy, infrared spectroscopy, and electrochemical workstation. The results show that the synergistic effect of coral like micro-nano structure constructed by anodic oxidation and low surface energy oxalic acid endows 7075 aluminum alloy with superhydrophobic property. When the concentration of oxalic acid is 40 g/L, the current density is 20 A/dm², and the anodizing time is 10 min, superhydrophobic aluminum alloy surface shows the largest contact angle of 152°, and the outstanding corrosion resistance, which is 4 orders of magnitude lower than that of the aluminum alloy matrix, and the excellent antifouling as well as self-cleaning properties.

Effect of laser shocking on surface integrity of 690 high strength steel

Cao Chen, Huang Chunling, Cao Yupeng, Yang Yang, Yang Cong

2021, 46(9): 247-251. doi:10.13251/j.issn.0254-6051.2021.09.044

Abstract ( 51 )

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In order to study the effect of laser shocking treatment on the surface integrity of 690 high strength steel, pulsed lasers with different power densities were used to shock the steel specimens. With the help of optical profiler, X-ray stress meter, hardness tester and transmission electron microscope, the surface three-dimensional morphology, hardness, residual stress and microstructure of the 690 high strength steel before and after laser shocking were measured and analyzed. The results show that after laser shocking with different power densities, the surface roughness of the specimen increases; with the increase of laser power density, the maximum height R_y of the specimen surface profile increases from 1.814 μm to 3.247 μm. After laser shocking with different power densities, the average residual stress of the specimen increases from －122 MPa to －296 MPa, and the average microhardness increases from 277 HV0.1 to 355 HV0.1. Compared with the specimen without laser shocking, the laser shocking treatment makes the surface grains of the 690 high strength steel continue to be refined, and the greater the power density, the smaller the surface grain size of the steel.

Effect of laser process parameters on crack rate and microstructure of Ni60/WC clad coating

Zhou Jianbo, Zhang Jing, Zhang Leitao, Li Haitao, Fan Shuaiqi, Xu Jinfu

2021, 46(9): 252-257. doi:10.13251/j.issn.0254-6051.2021.09.045

Abstract ( 53 )

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Effects of laser power (P), scanning speed (v), overlap rate (O) and powder feeding rate (Q) on the crack rate and microstructure of Ni60 /WC coating were studied by single factor test. The phase composition and element distribution of the coating were analyzed by means of energy spectrometer and X-ray diffraction. The results show that the crack rate is directly proportional to the P and inversely proportional to the v. Under the appropriate P and v, the effect of both O and Q on crack rate is not obvious. Both the coating and the substrate can form a good metallurgical bond, and each parameter has no obvious influence on the crystal growth pattern. The whole molten pool is successively composed of planar crystal region, cellular crystal region, relatively fine dendrite region and fine equiaxial crystal region from bottom to top. The grain size is mainly determined by the cooling rate ε. The grain size is directly proportional to the P and inversely proportional to the v and O. However, with the increase of Q, the grain size first decreases and then increases. The Ni60/WC coating is mainly composed of γ-(Fe, Ni), W₂C, Fe₃W₃C, M₇C₃, M₂₃C₆ and Ni₄W, etc, among which the WC part exists in the form of particles, playing the role of second phase strengthening, and part of WC form alloy carbide with Fe, Ni and other elements in the molten pool, in the grain boundary precipitation network, playing the role of grain boundary strengthening.

Friction and wear properties of nitrided layer of TD3 titanium alloy

Li Jingyang, Wang Wenbo, Qin Lin, He Longbin, La Lingmin, Zhang Jianlin, Duan Xinglu

2021, 46(9): 258-261. doi:10.13251/j.issn.0254-6051.2021.09.046

Abstract ( 60 )

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TD3 titanium alloy was nitrided by plasma surface nitriding technology, and microstructure, phase composition and hardness of the nitrided layer were tested. The friction and wear experiments of the TD3 alloy before and after nitriding were carried out at room temperature (25 ℃) and 600 ℃ respectively, and the effect of friction temperature on the friction coefficient, wear scar morphology and wear rate of which were analyzed. The results show that after plasma nitriding, a certain thickness of nitrided layer is formed on the surface of the TD3 alloy. While reducing the friction coefficient, the nitrided layer significantly reduces the wear rate of the TD3 alloy. When the temperature rises from 25 ℃ to 600 ℃, the wear scar morphology changes greatly, and the friction coefficient and wear rate also increase to a certain extent.

Analysis on cold bending fracture of wear-resistant steel NM400

Wu Hao, Deng Xiangtao, Li Chengru, Sui Yi, Zhang Tao, Ji Wenbo, Wang Zhaodong

2021, 46(9): 262-267. doi:10.13251/j.issn.0254-6051.2021.09.047

Abstract ( 82 )

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Aimed at the cold bending fracture in 20 mm thick NM400 plates, the cold bending process parameters, tensile properties, microstructure, inclusion types and size distribution were investigated to find the cause of fracture. The results show that bending fracture in NM400 plate is mainly caused by micron-size TiN inclusions. During the cold bending deformation, the stress concentration at the interface between inclusion and matrix leads to the nucleation and propagation of microcracks, and eventually leads to cold bending fracture. By reducing N content to below 4×10^-5, the cracking risk during cold bending process of NM400 steel is disappeared.

Failure analysis of 38CrMoAlA steel driveshaft

Xu Qihao,Yang Lilin, Xia Ming, Qin Chen, Geng Zhenyue, Jiang Yajun, Zhao Liping

2021, 46(9): 268-272. doi:10.13251/j.issn.0254-6051.2021.09.048

Abstract ( 57 )

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Chemical composition, non-metallic inclusions, fracture crack morphology, microstructure and hardness of a failed 38CrMoAlA steel shaft were tested and observed by using spectrometer, Zeiss metallographic microscope and Rockwell hardness tester, and influencing factors of the workpiece crack were discussed. The results show that the chemical composition, hardness, nitriding layer, non-metallic inclusions, and band structure of the 38CrMoAlA steel shaft meet the standard requirements. But the microstructure of the shaft is bainite+pearlite, which is unexpected structure (tempered sorbite), and meantime, the grain is coarse. Therefore, the workpiece has high core hardness, large internal stress and brittleness, and it is easy to produce cracks under the action of stress, leading to brittle fracture failure.

Numerical simulation and experimental verification of induction hardening of wind power inner gear ring

Ye Xiaofei, Zhang Wen, Mi Yanjun, Zhu Baizhi, Zhang Yusuo, Yi Liang, Huang Zhenjian

2021, 46(9): 273-278. doi:10.13251/j.issn.0254-6051.2021.09.049

Abstract ( 59 )

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Based on the electromagnetics-thermal-microstructure-mechanical coupled field, the microstructure, temperature distribution and stress of induction hardening process of wind turbine gear ring were calculated and the reliability of simulation was verified by hardened case contrast and hardness test. According to Maxwell equation and Fourier law, the temperature change of the gear ring surface during inductive heating and quenching was calculated, and then the microstructure transformation and final hardened profile of the gear ring at a specific position were calculated using the isoconversional model and the K-M equation. Finally, the residual stress distribution of the gear ring after induction hardening was calculated by using the thermo-elastoplastic constitutive equation. The results show that the temperature of the tooth root is the highest, the tooth tip is the lowest, and the tooth surface is between the two locations. In general, the hardened profile at the tooth surface is thicker, and at the tooth root and tooth tip are slightly smaller, but the hardened profile is evenly distributed in the middle of the gear surface. For residual stress distribution, the axial stress at the tooth root is compressive stress-tensile stress-compressive stress distribution from the beginning to the end, and the tangential stress is also compressive stress-tensile stress-compressive stress distribution from the beginning to the end. The axial stress at the tooth profile is compressive stress, which is distributed in small middle ends from the beginning to the end, while the tangential stress is compressive stress, which decreases gradually from the beginning to the end.

Finite element simulation of quenching process of large aluminum alloy forgings

Yu Chunpeng, Wang Liqiang, Tang Zhentao, Chen Lili

2021, 46(9): 279-283. doi:10.13251/j.issn.0254-6051.2021.09.050

Abstract ( 58 )

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Finite element software DEFORM V11 was used to calculate the surface integrative heat-exchange coefficient of T-shape 7N01 aluminum alloy forgings, to simulate the change rules of temperature field, stress field and deformation displacement during the quenching process of forgings, and to analyze the influence and mechanisms of temperature and heat stress on the quenching deformation of forgings. The results show that at the preliminary stage of quenching, due to the big differences in temperature gradient (the maximum temperature difference reached 225 ℃) and heat stress, the forgings generate the maximum elastic and plastic deformation at quenching time of 10 s on the side with ribbed plate, which is much bigger than that on the side without ribbed plate, and the bending curvature increases. At the middle stage of quenching, the forgings mainly generate elastic deformation, but contraction deformation is intensified on the side with thicker ribbed plate, the curvature decreases, and the forgings generate basically no further deformed at 50 s. And at the later stage of quenching, as the heat stress tends to zero, the forgings generate tiny elastic deformation due to cooling, and after the end of quenching, the forgings generate plastic bending deformation towards the ribbed plate as a whole, with greater radius of curvature than that before heating.

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