20 July 2022, Volume 46 Issue 7

    

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Testing & Research
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  Nanoindentation Mechanical Properties and Strengthening Mechanism of Magnetron Sputtered Al-Cu Alloy Films

  SHANGGUAN Fujun, SHANG Hailong, MA Bingyang, LI Wenge, ZHAO Yuantao, LIU Fukang, YU Dayi

  Materials For Mechanical Engineering. 2022, 46(7): 1-5,10. https://doi.org/10.11973/jxgccl202207001

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  Al-Cu alloy films with copper atomic fractions of 0-11.8% were prepared on stainless steel by magnetron sputtering method. The effects of copper content on the microstructure, nanoindentation mechanical properties and strengthening mechanism of the films were investigated. The results show that the pure aluminum film had a face-centered cubic structure. When the copper atomic fraction was between 2.2% and 6.5%, supersaturated solid solution phases were formed in Al-Cu alloy films. When the copper atomic fraction exceeded 6.5%, AlCu compounds were formed in films. With the increase of copper content, the grain size of the film decreased, and the hardness and elastic modulus increased. When the copper atomic fraction increased to 11.8%, the grain size was 34.7 nm, and the hardness and elastic modulus increased by 212.5% and 2.2% those of the pure aluminum film, respectively. When the copper atomic fraction was between 0 and 6.5%, the strengthening of films mainly depended on grain refinement strengthening and solid solution strengthening. When the copper atomic fraction exceeded 6.5%, the strengthening of films was determined by the combination of grain refinement strengthening, solid solution strengthening and second phase strengthening.
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  Influence of Forging Temperature on Microstructure and Tensile StrengthAeolotropy of TA15 Titanium Alloy

  WANG Zhe, RAN Xing, LIU Chengcheng, WANG Xin

  Materials For Mechanical Engineering. 2022, 46(7): 6-10. https://doi.org/10.11973/jxgccl202207002

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  TA15 titanium alloy bars were fored in (α+β) phase region, and the effect of three forging temperatures, namely t_β-15℃, t_β-30℃ and t_β-50℃ (t_β was β phase transition temperature), on the microstructure and tensile strength aeolotropy of the alloy was investigated. The results show that with the decrease of forging temperature, the content of primary α_p phase in the TA15 titanium alloy increased while that of lamellar α phase decreased, and the thickness and aspect ratio of lamellar α phase decreased; therefore the tensile strength increased. After forging at T_β-50℃, the tensile strength along the streamline direction of the TA15 titanium alloy reached 973 MPa. The tensile strength difference in three directions decreased with decreasing forging temperature. The tensile fracture of the forged TA15 titanium alloy was ductile fracture. The lower the forging temperature, the higher the content of primary α_p phase, the deeper the dimples on fractures; when more slender lamellar α phases existed, the fracture dimples were shallower.
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  Corrosion Fatigue Behavior of 0.6Zr3Mo Titanium Alloy in Gelled Acid withDifferent Concentrations of Hydrochloric Acid

  LI Yuze, LI Zhen, HE Shilei, WEI Wenlan, JIN Dandan, CUI Lu, CHENG Jiarui

  Materials For Mechanical Engineering. 2022, 46(7): 11-15,22. https://doi.org/10.11973/jxgccl202207003

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  The corrosion fatigue behavior of 0.6Zr3Mo titanium alloy in gelled acid with different mass fractions (1%-20%) of hydrochloric acid was studied by fatigue test with stress amplitude of 550 MPa and stress ratio of -1. The results show that the corrosion fatigue life of titanium alloy decreased linearly with increasing hydrochloric acid concentration, and its dispersion increased obviously. The corrosion fatigue fracture morphology of titanium alloy in gellic acid with 1wt% hydrochloric acid was similar to that in atmospheric environment; the crack source was single, and there was cleavage plane in the crack propagation zone; the main reason for fracture of titanium alloy was cyclic stress. When the mass fraction of hydrochloric acid in gellic acid was 10% and 15%, there were a lot of pits in the crack source zone, and the crack initiation was multi-source; the crack propagation zone included cleavage plane, primary cracks and a large number of secondary cracks; the joint action of cyclic load and hydrochloric acid accelerated the crack propagation and reduced the corrosion fatigue life of titanium alloy. In the crack propagation zone, the difference of local hydrochloric acid concentration at the crack tip led to deep secondary cracks, which was the main reason for the significant dispersion of corrosion fatigue life.
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  Effect of Micro Super-Fine-Polishing Treatment on Wear Performance of Cemented Carbide Milling Cutters

  SHI Jianmeng, DONG Weiping, CHENG Shumin, GUAN Yanying, LIU Zhen, WANG Junbin, SHI Hailan, LIU Daoxin

  Materials For Mechanical Engineering. 2022, 46(7): 16-22. https://doi.org/10.11973/jxgccl202207004

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  Micro super-fine-polishing treatment (MST) was conducted on cemented carbide milling cutters before and after surface ion-plating TiAlN coatings. The effect of MST on the wear behavior and wear mechanism of the cutters was analyzed by methods such as scratch tests, wear loss measurement, roughness testing, morphology observation and composition analysis. The results show that applying MST after plating did not affect the bond strength of the coating and could reduce the surface roughness of the cutter, thereby reducing the cutting resistance; so the wear resistance of the MST cutter was significantly better than that of the cutter without MST. Although applying MST first and then preparing the coating could reduce the surface roughness of the cutter, it deteriorated the bonding performance of the coating, thereby affecting the effective protection of the coating on the cutter; so the wear resistance of the MST cutter was poorer than that of the cutter without MST. The wear mechanisms of the cemented carbide cutters were adhesive wear and oxidative wear, and applying MST after plating could inhibit adhesive wear and oxidative wear.
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  Effects of Trace Chromium Addition and Rapid Solidification on Characteristicsof Sn-9Zn Alloy Solder and Solder/Copper Joint Interface

  FU Tian, ZHAO Guoji

  Materials For Mechanical Engineering. 2022, 46(7): 23-26. https://doi.org/10.11973/jxgccl202207005

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  Sn-9Zn and Sn-9Zn-0.1Cr (mass fraction/%) alloy solders were prepared by vacuum melting, and then the rapidly solidified Sn-9Zn-0.1Cr alloy solder was obtained by a single roll method. The effects of the trace chromium addition and rapid solidification on the solder microstructure, wetting properties and corrosion resistance, as well as on the growth kinetics of intermetallic compound (IMC) layers at the solder/copper joint interface during aging at 85℃, were investigated. The results show that the addition of 0.1wt% chromium could inhibit the aggregation of zinc-rich phases and refine the eutectic structure in the Sn-9Zn alloy solder, increase the maximum wetting force and shorten the wetting time of the alloy solder, and inhibit the formation and the overgrowth during aging of the interfacial IMC layer of the solder/copper joint. The zinc-rich phase in the rapidly solidified Sn-9Zn-0.1Cr alloy solder was granular and dispersed in β-Sn dendrites, the structure was finer and more uniform, and the corrosion resistant was significantly improved; but the growth rate of the interfacial IMC layer during aging at 85℃ slightly increased compared with that of the as-smelted alloy solder.
New Materials & Technology
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  Preparation and Thermophysical Properties of New Composite Oxides for Thermal Barrier Coating

  RAN Shuming

  Materials For Mechanical Engineering. 2022, 46(7): 27-31,37. https://doi.org/10.11973/jxgccl202207006

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  Taking La₂O₃, MgO, SrCO₃, CeO₂ and Ta₂O₅ with high purity as raw reactants, the Sr₃La₃Ce₇Ta₂O_26.5 and Mg₃La₃Ce₇Ta₂O_26.5 oxides were synthesized by multi-step high temperature sintering, and the crystal structure, microstructure and thermophysical properties were investigated. The results show that the obtained oxides exhibited a single pyroxhlore crystal structure; the microstructure was very dense, and the grain boundaries were very clear; the element composition and the corresponding mole ratio were consistent with the corresponding chemical formula. The thermal expansion coefficient of Sr₃La₃Ce₇Ta₂O_26.5 was larger than that of Mg₃La₃Ce₇Ta₂O_26.5, and the thermal expansion coefficients at 1 000℃ were 11.6×10^-6, 11.37×10^-6 K^-1, respectively, which were obviously larger than 9×10^-6 K of 7YSZ; the two oxides had good crystal structure stability at high temperature. The thermal conductivity at 1 200℃ of Sr₃La₃Ce₇Ta₂O_26.5 and Mg₃La₃Ce₇Ta₂O_26.5 were 1.68,1.87 W·m^-1·K^-1, respectively, which were smaller than 2 W·m^-1·K^-1 of 7YSZ; the large ionic radius and atomic mass of Sr²⁺ resulted in the lower thermal conductivity of Sr₃La₃Ce₇Ta₂O_26.5 than Mg₃La₃Ce₇Ta₂O_26.5. The thermal conductivity and expansion coefficient of the synthesized oxides both satisfied the requirements for thermal barrier coating.
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  Fabrication and Heat Transfer Performance of Multi-scaleComposite Structure Porous Wick Heat Pipe

  JIANG Xuewei, LIAN Lixian, TANG Hai, LIU Ying

  Materials For Mechanical Engineering. 2022, 46(7): 32-37. https://doi.org/10.11973/jxgccl202207007

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  According to functional differences of different parts of a heat pipe, a novel multi-scale composite structure porous wick heat pipe was designed and fabricated with nano-porous copper powder and irregular copper powder as raw materials. The porous wick at evaporation section of the heat pipe consisted of a two-layer structure, namely a small-pore layer sintered with nano-porous copper powder on the pipe wall side and a large-pore layer sintered with irregular copper powder on the working medium chamber side. The porous wick at adiabatic section and condensation section had one large-pore layer sintered with irregular copper powder. The heat transfer performance of the heat pipe was investigated by using a self-assembled heat transfer performance test device. The results show that the small-pore layer of the multi-scale composite structure porous wick could provide higher capillary forces, and the large-pore layer could provide larger working medium flow channels, thereby improving the heat transfer capacity of the heat pipe. Comparing with the monolayer uniform porous wick heat pipe, the multi-scale composite structure porous wick heat pipe exhibited a higher heat transfer ability under anti-gravity conditions; and the heat transfer limit power was as high as 90 W under the completely anti-gravity condition (tilt angle of 90°), which was 2.9 times and 2.3 times higher than that of monolayer uniform porous wick heat pipes prepared with nano-porous copper powder and irregular copper powder, respectively.
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  Preparation and Supercapacitive Performance of Metal-Organic Framework Derived NiCo₂O₄/rGO Composites

  SHI Zhongting, MIAO Tianyu, ZHAO Bin

  Materials For Mechanical Engineering. 2022, 46(7): 38-46. https://doi.org/10.11973/jxgccl202207008

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  Nickel-cobalt metal-organic framework(Ni-Co-MOF)/graphene oxide(GO) precursors were prepared by solvothermal synthesis with mass ratios of nickel and cobalt metal salts to GO of 1：0.05, 1：0.07, and 1：0.09, respectively, and then were ultrasonically sprayed on the heated nickel foam substrate to obtain NiCo₂O₄/reduced graphene oxide(rGO) composite electrode materials. The microstructure and electrochemical properties of the composites were studied. The results show that the NiCo₂O₄/rGO composite was composed of wrinkled graphene and NiCo₂O₄ nanoparticles uniformly distributed on graphene surface. When the mass ratio of salt to GO was 1：0.07, the composite had a high specific capacitance of 991 F·g^-1 at a current density of 2 A·g^-1; after 30 000 cycles of charge and discharge at a current density of 20 A·g^-1, the initial capacitance retention was still as high as 126%. The assembled NiCo₂O₄/rGO//AC asymmetric supercapacitor had an energy density of 41 W·h·kg^-1 at a power density of 1 604 W·kg^-1, and achieved capacitance retention greater than 100% after 25 000 charge/discharge cycles, showing an ultra-long cycle life.
Material Properties & Application
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  Fatigue Properties of CO₂ Gas Shielded Welded Joint of High Strength and Toughness Medium-Mn Steel

  QI Xiangyu, YAN Ling, DU Linxiu, LI Guanglong, ZHANG Peng, WANG Xiaohang

  Materials For Mechanical Engineering. 2022, 46(7): 47-50,56. https://doi.org/10.11973/jxgccl202207009

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  The butt welding test of 30 mm thick high strength and toughness medium-Mn steel plate was carried out by CO₂ gas shielded welding. The stress amplitude-life curves of medium-Mn steel welded joints were obtained by round bar tensile and compressive fatigue test. The high cycle fatigue limit was measured and its fracture morphology was observed. The results show that the high cycle fatigue limit of medium-Mn steel welded joint was 353 MPa at stress ratio of -1 and 10⁷ cycles. When obvious welding defects existed in the medium-Mn steel welded joint, the fatigue crack initiated at the microscopic defects. When no welding defects existed in the weld, the fatigue crack initiated at the fusion line of the sample surface. The surface of the fatigue crack propagation zone was rough, and obvious secondary cracks existed. There were a large number of uniform and fine dimples on the surface of the transient fracture area.
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  Effect of Austempering Time on Contact Fatigue Performance of SAE8620 Bearing Steel for Railway Locomotive

  ZHANG Wenkai, YANG Zhen, WANG Kecheng

  Materials For Mechanical Engineering. 2022, 46(7): 51-56. https://doi.org/10.11973/jxgccl202207010

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  The surface carburized SAE8620 bearing steel was austenitized at 855℃, then subjected to austempering in a salt bath at 225℃, and then tempered at 225℃. The effects of austempering time (7, 21 h) on the microstructure, phase composition, hardness and contact fatigue properties of the test steel were investigated. The results show that the surface microstructure of the test steel was composed of bainitic ferrite, retained austenite, martensite and carbides when austempered for 7 h. When austempered for 21 h, the martensite in the surface structure disappeared, the average width of bainite laths increased, the content of acicular bainitic ferrite increased and that of the retained austenite decreased. The test steel austempered for 7 h had higher surface hardness and a longer contact fatigue life than the steel austempered for 21 h, which was mainly related to the better resistance to plastic deformation due to the more retained austenite, smaller average width of bainite laths in the surface and higher surface hardness.
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  Effect of Mechanical Stirring and Ultrasonic Processing on Microstructure andTribological Properties of Nano-SiC_p/Zn-Al Composites

  LIU Sheng, FANG Zihao, ZOU Pei, PENG Tian

  Materials For Mechanical Engineering. 2022, 46(7): 57-63. https://doi.org/10.11973/jxgccl202207011

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  Nano-SiC_p/Zn-Al composites with 0.1mass% SiC_p were prepared by direct smelting and by applying mechanical stirring, ultrasonic processing, and simultaneous mechanical stirring and ultrasonic processing during smelting, respectively. The effects of smelting process on the microstructure, microhardness and friction and wear properties were studied. The results show that the microstructures of samples obtained by different smelting processes were all mainly composed of α(Al,Zn) Al-rich phase and η(Al,Zn) Zn-rich phase, and the microhardness had little difference. After direct smelting and smelting with mechanical stirring, ultrasonic processing, simultaneous mechanical stirring and ultrasonic processing, the dispersion effect of SiC_p in the composite was successively enhanced, the grain size became more uniform in turn, and the average friction factor was 0.38, 0.33, 0.32, 0.31, respectively. Under conditions of small-load low-frequency, small-load high-frequency, medium-load high-frequency, large-load high-frequency, the wear loss of the sample obtained by applying mechanical stirring and ultrasonic processing during smelting was reduced by 77.4%, 52.9%, 43.3% and 52.5%, respectively, comparing with that by the direct smelting. The wear mechanisms were all adhesive wear.
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  Room Temperature Deformation Behavior of New Heat Resistant Austenitic Steel SP2215

  SONG Li

  Materials For Mechanical Engineering. 2022, 46(7): 64-69,75. https://doi.org/10.11973/jxgccl202207012

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  Compression (with 10%-50% deformation), tension (with 10%-40% deformation) and bending (with 20°-180° bending angle) deformation tests at room temperature were conducted on SP2215 heat resistant austenitic steel. The microstructure, microhardness and strength of the steel after room temperature deformation were studied. The results show that no martensitic transformation occurred in SP2215 steel during room temperature deformation. The steel had high austenite structure stability. Dislocation slips always took part in deformation. Room temperature deformation could greatly improve the work hardening of SP2215 steel, thereby increasing the tensile strength and hardness, and doubling the yield strength.
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  Effect of Vanadium Content on Microstructure and Mechanical Properties of 4Cr5Mo2V Steel

  HUANG Shan, WU Riming, CHEN Meng, HU Tao, DONG Jinhua

  Materials For Mechanical Engineering. 2022, 46(7): 70-75. https://doi.org/10.11973/jxgccl202207013

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  On the basis of chemical composition of 4Cr5Mo2V steel, test steels with vanadium mass fractions of 0.15%, 0.55% and 1.25% were prepared, and then vacuum quenched at 1 040℃ and tempered at different temperatures (540, 620℃). The effect of vanadium content on the microstructure, hardness and impact toughness of the test steel was investigated. The results show that with the increase of vanadium content, the grains in all the tempered test steels were refined, and the number of precipitated VC-type carbides increased; the grain refinement and precipitation strengthening effects were enhanced, resulting in the increased hardness. The number of precipitated carbides after tempering at 650℃ was larger, leading to the softening of the matrix, therefore the hardness decreased compared with that tempered at 540℃. After tempering at 540℃, the test steel with vanadium content of 0.15% and 0.55% had ductile fracture, and the latter had better impact toughness, whose impact absorbing energy reached 265 J; when the vanadium content increased to 1.25%, the test steel had brittle fracture, and the impact absorbing energy was only 26 J. After tempering at 620℃, ductile fracture occurred in all three test steels, and the impact absorbing energy was greater than 200 J.
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  Effects of Trace Zirconium on Microstructure and Mechanical Properties of AlSn6Cu Alloy

  ZHAI Yong, ZHAO Jun, SUN Shaobo, HAN Xinzhan

  Materials For Mechanical Engineering. 2022, 46(7): 76-81. https://doi.org/10.11973/jxgccl202207014

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  A trace amount of zirconium was introduced into the as-cast AlSn6Cu alloy by adding with Al-5Zr master alloy, and the effect of zirconium content (0-0.25%, mass fraction) on the microstructure and mechanical properties of the alloy was investigated. The results show that the addition of zirconium element had an obvious effect of grain refinement, and the grain size could be reduced from 1 450 μm to 280 μm by adding 0.25% zirconium. With the increase of zirconium content, the microstructure of the alloy underwent the transformation from dendritic to degenerated dendritic or petal-like, and then to near-spherical forms; the morphology of β-Sn phase changed from granular to vermicular, and then to reticular. The tensile strength of the alloys with zirconium was lower than that without zirconium. But with the increase of zirconium content, the tensile strength of the alloys with zirconium increased gradually and finally tended to be stable. The variation trend was the result of competition between fine-grain strengthening and grain boundary weakening produced by β-Sn phase. With the increase of zirconium content, the hardness of the alloy increased first and then decreased.
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  Intergranular Cracking Analysis in Heat-Affected Zone on TP347H Steel Side of T91/TP347H Dissimilar Steel Joint in Service

  LI Yong

  Materials For Mechanical Engineering. 2022, 46(7): 82-89. https://doi.org/10.11973/jxgccl202207015

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  Intergranular cracks were found in T91/TP347H dissimilar steel joint of a boiler panel superheater in a power plant after 80 000 h operation. The cracks were located in the heat-affected zone on TP347H austenitic steel side. The features and forming causes of the intergranular cracking and its effect on the mechanical properties were analyzed by microstructure observation, hardness test and tensile test. The results show that the intergranular cracks existed at the fusion line on TP347H steel side, and were intergranular corrosion cracks. The cracks penetrated through 3-4 grains and were filled with oxides inside. The hardness and tensile strength of the panel superheater tube joint with intergranular cracks met the requirements, but the plasticity was poor. Coarse grains and fast cooling rates after welding made the heat affected zone on the TP347H steel side of the panel superheater tube joint prone to forming depletion of chromium at grain boundaries during high-temperature service, causing intergranular corrosion. The high hardness gradient near the fusion line on the TP347H steel side led to stress concentration here, accelerating the generation of intergranular corrosion cracks.
Physical Simulation & Numerical Simulation
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  High Temperature Plasticity of X65 Grade Cu-bearing Pipeline Steel

  LI Yuchen, SHI Xianbo, YAN Wei, SHAN Yiyin, REN Yi, SHEN Minggang, WANG Yiyong

  Materials For Mechanical Engineering. 2022, 46(7): 90-94. https://doi.org/10.11973/jxgccl202207016

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  The high temperature tensile test of X65 grade low carbon low nickel Cu-bearing pipeline steel containing 1.8wt% copper and 1.0wt% nickel was carried out with Gleeble-3800 thermal simulation testing machine to study the high temperature plasticity at different temperatures (850-1 300℃). The results show that the tensile strength of the Cu-bearing pipeline steel showed an overall downward trend with increasing test temperature; the tensile strength at 850℃ reached 105 MPa, while the tensile strength at 1 300℃ was reduced to about 30 MPa. With increasing test temperature, the percentage reduction of area of the Cu-bearing pipeline steel showed an overall increase trend. When the test temperature was higher than 1 050℃, the percentage reduction of area was above 80%, showing good high temperature plasticity; the percentage reduction of area at 850-1 000℃ was about 60%, indicating the large deformation of the pipeline steel should be avoided in the range of 850-1 000℃. When the test temperature was higher than 1 050℃, the improvement of plasticity was related to dynamic recrystallization. In the continuous casting temperature range (1 100-1 250℃), the Cu-bearing pipeline steel had excellent high temperature plasticity, which could ensure the metallurgical quality of the continuous casting billet.
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  Numerical Simulation of Residual Stress in Friction Stir Lap Welding of Al-Mg Dissimilar Alloy

  WU Xiaohu, CAO Lijie, MIAO Chenhuai, WANG Yi

  Materials For Mechanical Engineering. 2022, 46(7): 95-102. https://doi.org/10.11973/jxgccl202207017

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  The sequential thermo-mechanical coupling method was used to establish the model,and through the orthogonal experiment, the effects of welding speed, overlap amount and stirring tool rotation speed of friction stir lap welding on the residual stress of Al-Mg dissimilar alloy were analyzed by ABAQUS software. The optimal process parameters were obtained. The simulation was verified by tests. The effects of welding speed and overlap amount on the residual stress were studied. The results show that the optimal parameters of friction stir lap welding were welding speed of 60 mm·min^-1, overlap amount of 60 mm and stirring tool rotation speed of 1 400 r·min^-1. In different welding processes, the simulation of thermal cycle curves and residual stress were consistent with the experimental results, and the relative errors were less than 7.5% and 8.4%, respectively, which verified the accuracy of the simulation. The maximum residual stress appeared at the overlap surface at the end of the weld, and the maximum longitudinal residual stress in the optimal welding process was 137.7 MPa. Compared with the rotation speed of the stirring tool, the welding speed and the overlap amount had a great influence on the residual stress. With increasing welding speed, the peak value of the longitudinal residual compressive stress increased,and the range of compressive stress became narrower; with increasing overlap amount, the peak value of longitudinal residual compressive stress decreased and the range of compressive stress became wider.