In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-si...In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones.It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ)through the thickness direction.The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld,and the microhardness values decreased from both surfaces to the middle of the NZ.The lowest hardness zone(LHZ)exhibited a"hyperbolical"-shaped distribution extending to the middle of the NZ.Similar tensile properties were obtained in the three sliced specimens of the FSW joint,and the joint coefficient reached about 70%which achieved the same level as the conventional FSW Al alloy joints.Finite element modeling proved that the"hyperbolical"-shaped heat affected zone(HAZ)was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength.Based on the analysis of the hardness contour map,tensile property and microstructural evolution of the joints,an Isothermal Softening Layer(ISL)model was proposed and established,which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.展开更多
Most of the investigations regarding friction stir welding(FSW)of aluminum alloy plates have been limited to about 5 to 6mm thick plates.In prior work conducted the various aspects concerning the process parameters an...Most of the investigations regarding friction stir welding(FSW)of aluminum alloy plates have been limited to about 5 to 6mm thick plates.In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy.Two different simple-tomanufacture tool geometries were used.The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined.It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates,tool having trapezoidal pin geometry was suitable.Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min.At very low and high dwell time the ductility of welded joints are reduced significantly.展开更多
It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional frict...It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.展开更多
Multi-pass friction stir processing(M-FSP)was performed to repair the interface defects of AA5083/T2 copper explosive composite plates.The interface morphology and its bonding mechanism were explored.The results show ...Multi-pass friction stir processing(M-FSP)was performed to repair the interface defects of AA5083/T2 copper explosive composite plates.The interface morphology and its bonding mechanism were explored.The results show that higher rotation speed and lower transverse speed produce more heat generated during FSP.The defect-free and good mechanical properties of the AA5083/T2 copper composite plate can be obtained under the condition of the rotation speed of 1200 r/min,the transverse speed of 30 mm/min and the overlap of 2/24.Moreover,M-FSP changes the interface bonding mechanism from metallurgical bonding to vortex connection,improving the bonding strength of composite plate,which can guarantee the repairing quality of composite plates.展开更多
Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configuration...Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configurations, namely inclined butt(conventional butt) and serrated interlocking(innovative butt), are proposed for improving weld formation and joint quality. The results show that a continuous and straight intermetallic compound layer appears at the Mg side interface in conventional butt joint, and the maximum average thickness reaches about 60.1 μm.Additionally, the Mg side interface also partially melts, forming a eutectic structure composed of Mg solid solution and Al_(12)Mg_(17) phase.For the innovative butt joint, the Mg side interface presents the curved interlocking feature, and intermetallic compounds can be reduced to less than 10 μm. The joint strength of innovative butt joint is more than three times that of conventional butt joint. This is due to the interlocking effect and thin intermetallic compounds in the innovative joint.展开更多
TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning elect...TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy（FESEM） and X-ray diffraction（XRD）, respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy（SEM）, energy disperse spectroscopy（EDS）, and optical microscope（OM）, respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of（Ti, Al）N, AlTiN, and TiN hard phases, Si_3N_4 exists between the（Ti, Al）N crystal grains, increasing the coating microhardness to 3200 HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction（COF） of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.展开更多
The skin friction and heat transfer occurring in the laminar boundary layerwhich caused by a vertical liquid jet impinging on a continuously moving horizontal plate werestudied. Similarity solutions for shear stress a...The skin friction and heat transfer occurring in the laminar boundary layerwhich caused by a vertical liquid jet impinging on a continuously moving horizontal plate werestudied. Similarity solutions for shear stress and heat distribution were obtained by using thehooting technique. The results show that the skin friction decreases with an increase of velocityparameter, the evolving of thermal boundary decrease with increasing in Prandtl number, but increasewith increasing of velocity parameter.展开更多
In this work, 20-mm-thick aluminum-alloy plates were joined via friction stir welding. The temperature gradient was reduced by reducing the surface welding heat input to achieve uniformity of the mechanical properties...In this work, 20-mm-thick aluminum-alloy plates were joined via friction stir welding. The temperature gradient was reduced by reducing the surface welding heat input to achieve uniformity of the mechanical properties across the thick plate joints. The welding temperature was measured using thermocouples. The microstructures were observed via electron backscatter diff raction and transmission electron microscopy. The tensile properties of the samples sliced along the thickness direction of the joint were evaluated. The results show that the highest welding peak temperature is 430℃ on the advancing side on the top surface of the joint. The grain size gradually decreased along the thickness direction, and grain refi nement was due to the combination of continuous, discontinuous, and geometric dynamic recrystallization. The tensile properties of the sliced samples were found to be uniform, and the ultimate tensile strength reached 62% of that of the base metal. The main strengthening mechanism of the Al–Zn–Mg–Cu alloy joints consists of precipitation strengthening. In addition, the η ` → η phase transition and grain coarsening in the heat-affected zone were found to be responsible for the fracture of the joints.展开更多
The rigid-interface friction model is usually used in the nonlinear vibrationof the rectangular plate with dry friction support edges. The present study provides an extensionby using a hysteretic spring friction model...The rigid-interface friction model is usually used in the nonlinear vibrationof the rectangular plate with dry friction support edges. The present study provides an extensionby using a hysteretic spring friction model and taking account of the stick-slip motion of theplate. Results for a range of problem parameters have been obtained. The results show that thenonlinear frequency response behavior of the system can be quite different from the rigid-interfacefriction model. The effects of the stiffness at friction interfaces and the stick-slip motion on thenonlinear vibration of the plate are significant and hence cannot be neglected.展开更多
The effects on the local skin friction of smooth flat plate by formation of air cavity are investigated experimentally,under the conditions of several variations of air injection angle,pore size,porous surface area an...The effects on the local skin friction of smooth flat plate by formation of air cavity are investigated experimentally,under the conditions of several variations of air injection angle,pore size,porous surface area and transverse step.The experimental results show that local skin friction of downstream of the porous section could be reduced at extent ranging from 50% to 90%,by injection air through pore or slot,with free stream velocities from 2 to 6 m/s.The pore size and area of air injection surface have small effect on skin friction reduction,step has significant effect on skin friction reduction.The mechanism of the skin friction reduction is due to the formation of air cavity,mixed with air and water,between the flat plate and its water boundary layer.展开更多
In this study, high velocity impact behaviour of friction stir welded AA7075-T651 25 mm thick plates were investigated using a 7.62 mm × 51 mm lead core and 7.62 mm × 39 mm steel core projectiles. Prior to b...In this study, high velocity impact behaviour of friction stir welded AA7075-T651 25 mm thick plates were investigated using a 7.62 mm × 51 mm lead core and 7.62 mm × 39 mm steel core projectiles. Prior to ballistic trails, mechanical and metallurgical properties of friction stir welded AA 7075-T651 25 mm thick plates were studied. Microstructural and hardness studies revealed that friction stir welds constituted three distinct regions namely Weld Nugget(WN), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). Base Material(BM) and all three weld regions were ballistically tested as per military standard NIJ.0108.01 using lead and steel core bullets at maximum permissible velocities of 830 ± 20 and 700 ± 30 m/s, respectively. It has been found that base material(AA7075-T651)and all three weld regions of 25 mm thick plates were able to resist perforation by both types of projectiles used. However depth of penetration has been found to increase from BM to WN, HAZ and TMAZ for both types of projectiles. In all cases steel core projectiles caused higher depth of penetration compared to those caused by lead core projectiles. TMAZs of the friction stir welds were found to be the weakest zone. The fracture that occurred in the base material was spall fragmentation indicating brittle failure, whereas all zones of friction stir welded AA7075-T651 targets with a front petalling, indicating ductile failure. The post-ballistic tested samples showed no significant change in the microstructure of the BM and WN. On the other hand, TMAZ and HAZ showed severe grain deformation in the direction of projectile penetration, and the formation of adiabatic shear bands(ASB). This work showed that 25 mm thick friction stir welded AA7075-T651 joints responded well to ballistic impact loads, making them a good choice for light combat vehicles.展开更多
Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials a...Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.展开更多
We focus on the friction loss measurement and reduction of the timing belt guide plates of a fourcylinder gasoline engine. To minimize the friction loss caused by the dynamic friction of the guide plates during timing...We focus on the friction loss measurement and reduction of the timing belt guide plates of a fourcylinder gasoline engine. To minimize the friction loss caused by the dynamic friction of the guide plates during timing belt motion and improve the efficiency of the internal combustion engine(ICE), we adopt four different plastic materials in fabricating the guide plates. With controlled engine boundary conditions and operational modes, an AVL electric dynamometer is used to measure the output of the engine. The results indicate that selecting polytetrafluoroethylene(PTFE) as the additive in fabricating the guide plates can effectively reduce the friction loss, so that the output torque and output power of the engine can be improved, thus reducing fuel consumptions. This work also has positive impact on the efficiency optimization of similar ICEs.展开更多
This study delves into both experimental and analytical examinations of heat exchange in a straight channel, where Al_(2)O_(3)-water nanofluids are utilized, spanning the Reynolds number spectrum from 100 to 1800. Div...This study delves into both experimental and analytical examinations of heat exchange in a straight channel, where Al_(2)O_(3)-water nanofluids are utilized, spanning the Reynolds number spectrum from 100 to 1800. Diverse volume fractions(1%, 2%, and 3%) of Al_(2)O_(3)-water nanofluids are meticulously prepared and analyzed. The essential physical properties of these nanofluids, critical for evaluating their thermal and flow characteristics, have been comprehensively assessed. From a quantitative perspective, numerical simulations are employed to predict the Nusselt number(Nu) and friction factor(f). The empirical findings reveal intriguing trends: the friction factor experiences an upward trend with diminishing velocity, attributed to heightened molecular cohesion. Conversely, the friction factor demonstrates a decline with diminishing volume fractions, a consequence of reduced particle size. Both the nanofluid's viscosity and heat transfer coefficient exhibit a rise in tandem with augmented volume flow rate and concentration gradient. Notably, the simulation results harmonize remarkably well with experimental data. Rigorous validation against prior studies underscores the robust consistency of these outcomes. In the pursuit of augmenting heat transfer, a volume fraction of 3% emerges as particularly influential, yielding an impressive 53.8% enhancement. Minor increments in the friction factor, while present, prove negligible and can be safely overlooked.展开更多
The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated.A three-dimensional Navier-Stokes(N-S)equation considering viscous force and inertial force rather than Reynol...The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated.A three-dimensional Navier-Stokes(N-S)equation considering viscous force and inertial force rather than Reynolds equation or modified Reynolds equation is presented to model the flow field.Pressure and temperature distribution in radial and circumferential direction under three different conditions,i.e.,isothermal,that considering viscosity-temperature characteristic as well as shear thinning non-Newtonian fluid are simulated,respectively,by utilizing the commercial computational fluid dynamics(CFD)software FLUENT.The results reveal that the grooves on the driven plate make the pressure,temperature distribution present periodic variation.The oil temperature and shear rate have important effects on the flow field between frictional pairs,and the oil temperature is more important parameter.The simulation results lay a theoretical foundation for the reasonable designs ofhydroviscous drive.展开更多
The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program th...The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program that has been developed. The computing results show themedium diameter orientation is unreliable, especially under the interference of an outer forcecouple. Under such working conditions, the circumferential traction distribution on the screw teethis extremely uneven, which is the main reason for the destruction and short life time ofscrew-pairs. When utilizing the same precision (the relative tolerance is 10X10^(-5)), themultipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory sizeis only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suitedfor computing large-scale engineering problems.展开更多
In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was inve...In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.展开更多
Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating und...Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.展开更多
Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by f...Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.展开更多
An analysis is performed to study the magnetohydrodynamic flow of an electrically conducting, viscous incompressible fluid past a semi-infinite vertical plate with variable surface temperature under the action of tran...An analysis is performed to study the magnetohydrodynamic flow of an electrically conducting, viscous incompressible fluid past a semi-infinite vertical plate with variable surface temperature under the action of transversely applied magnetic field. The heat due to viscous dissipation and the induced magnetic field are assumed to be negligible. The dimensionless governing equations are unsteady, two-dimensional, coupled and non-linear governing equations. It is found that the magnetic field parameter has a retarding effect on the velocities of air and water.展开更多
基金supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2017236)National Natural Science Foundation of China under grant No.U1760201.
文摘In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones.It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ)through the thickness direction.The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld,and the microhardness values decreased from both surfaces to the middle of the NZ.The lowest hardness zone(LHZ)exhibited a"hyperbolical"-shaped distribution extending to the middle of the NZ.Similar tensile properties were obtained in the three sliced specimens of the FSW joint,and the joint coefficient reached about 70%which achieved the same level as the conventional FSW Al alloy joints.Finite element modeling proved that the"hyperbolical"-shaped heat affected zone(HAZ)was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength.Based on the analysis of the hardness contour map,tensile property and microstructural evolution of the joints,an Isothermal Softening Layer(ISL)model was proposed and established,which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.
文摘Most of the investigations regarding friction stir welding(FSW)of aluminum alloy plates have been limited to about 5 to 6mm thick plates.In prior work conducted the various aspects concerning the process parameters and the FSW tool geometry were studied utilizing friction stir welding of 12 mm thick commercial grade aluminum alloy.Two different simple-tomanufacture tool geometries were used.The effect of varying welding parameters and dwell time of FSW tool on mechanical properties and weld quality was examined.It was observed that in order to achieve a defect free welding on such thick aluminum alloy plates,tool having trapezoidal pin geometry was suitable.Adequate tensile strength and ductility can be achieved utilizing a combination of high tool rotational speed of about 2000 r/min and low speed of welding around 28 mm/min.At very low and high dwell time the ductility of welded joints are reduced significantly.
基金financially supported by the National Natural Science Foundation of China(No.51905309)the Science and Technology Planning Project of State Grid Henan Electric Power Company(No.52170220009Y)。
文摘It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for medium-thick plates due to the inherent high heat generation rate at the shoulder-workpiece contact interface in conventional friction stir welding.Thus,doubleside friction stir welding is innovatively applied to join 12-mm medium-thick 6061-T6 aluminum alloy and pure copper dissimilar plates,and the effect of welding speeds on the joint microstructure and mechanical properties of Al/Cu welds is systematically analyzed.It reveals that a sound Al/Cu joint without macroscopic defects can be achieved when the welding speed is lower than 180 mm/min,while a nonuniform relatively thick intermetallic compound(IMC)layer is formed at the Al/Cu interface,resulting in lots of local microcracks within the first-pass weld under the plunging force of the tool during friction stir welding of the second-pass,and seriously deteriorates the mechanical properties of the joint.With the increase of welding speed to more than 300 mm/min void defects appear in the joint,but the joint properties are still better than the welds performed at low welding speed conditions since a continuous uniform thin IMCs layer is formed at the Al/Cu interface.The maximum tensile strength and elongation of Al/Cu weld are,respectively,135.11 MPa and 6.06%,which is achieved at the welding speed of 400 mm/min.In addition,due to the influence of welding distortion of the first-pass weld,the secondpass weld is more prone to form void defects than the first-pass weld when the same plunge depth is applied on both sides.The double-side friction stir welding is proved to be a good method for dissimilar welding of medium-thick Al/Cu plates.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(No.51505293)the Natural Science Foundation of Jiangsu Province,China(No.BK20190684)+1 种基金the Natural Science Research of the Jiangsu Higher Education Institutions of China(No.18KJB460016)the Key Laboratory of Lightweight Materials,Nanjing Tech University,as well as by a fellowship from the International Postdoctoral Exchange Followship Program(2020096 to Jian WANG).
文摘Multi-pass friction stir processing(M-FSP)was performed to repair the interface defects of AA5083/T2 copper explosive composite plates.The interface morphology and its bonding mechanism were explored.The results show that higher rotation speed and lower transverse speed produce more heat generated during FSP.The defect-free and good mechanical properties of the AA5083/T2 copper composite plate can be obtained under the condition of the rotation speed of 1200 r/min,the transverse speed of 30 mm/min and the overlap of 2/24.Moreover,M-FSP changes the interface bonding mechanism from metallurgical bonding to vortex connection,improving the bonding strength of composite plate,which can guarantee the repairing quality of composite plates.
基金supported by the National Natural Science Foundation of China (No.51874179,52005240 and 52164045)the Young Talent Program of Major Disciplines of Academic and Technical Leaders in Jiangxi Province (No.20212BCJ23028)。
文摘Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configurations, namely inclined butt(conventional butt) and serrated interlocking(innovative butt), are proposed for improving weld formation and joint quality. The results show that a continuous and straight intermetallic compound layer appears at the Mg side interface in conventional butt joint, and the maximum average thickness reaches about 60.1 μm.Additionally, the Mg side interface also partially melts, forming a eutectic structure composed of Mg solid solution and Al_(12)Mg_(17) phase.For the innovative butt joint, the Mg side interface presents the curved interlocking feature, and intermetallic compounds can be reduced to less than 10 μm. The joint strength of innovative butt joint is more than three times that of conventional butt joint. This is due to the interlocking effect and thin intermetallic compounds in the innovative joint.
基金Funded by the Jiangsu Province Science and Technology Support Program(Industry)(BE2014865)
文摘TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy（FESEM） and X-ray diffraction（XRD）, respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy（SEM）, energy disperse spectroscopy（EDS）, and optical microscope（OM）, respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of（Ti, Al）N, AlTiN, and TiN hard phases, Si_3N_4 exists between the（Ti, Al）N crystal grains, increasing the coating microhardness to 3200 HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction（COF） of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.
基金[This work was financially supported by "973" key foundation of China (No.G 1998061510).]
文摘The skin friction and heat transfer occurring in the laminar boundary layerwhich caused by a vertical liquid jet impinging on a continuously moving horizontal plate werestudied. Similarity solutions for shear stress and heat distribution were obtained by using thehooting technique. The results show that the skin friction decreases with an increase of velocityparameter, the evolving of thermal boundary decrease with increasing in Prandtl number, but increasewith increasing of velocity parameter.
基金supported by the National Natural Science Foundation of China(Nos.U1760201,51974220,52034005)the Innovation Capacity Support Project of Shaanxi Province(No.2020KJXX-077)+4 种基金the National Key Research and Development Program of China(No.2017YFB0306202)the Key Research and Development Program of Shaanxi Province(Grant No.2020ZDLGY13-06)the Key Industrial Research Program of Shaanxi Province(Grant No.2017ZDXM-GY-037)the Natural Science Basic Research Program of Shaanxi Province(Grant Nos.2019JQ-111,2019JQ-769)the Xi’an Science and Technology Project(Grant No.201805033YD11CG17(8))。
文摘In this work, 20-mm-thick aluminum-alloy plates were joined via friction stir welding. The temperature gradient was reduced by reducing the surface welding heat input to achieve uniformity of the mechanical properties across the thick plate joints. The welding temperature was measured using thermocouples. The microstructures were observed via electron backscatter diff raction and transmission electron microscopy. The tensile properties of the samples sliced along the thickness direction of the joint were evaluated. The results show that the highest welding peak temperature is 430℃ on the advancing side on the top surface of the joint. The grain size gradually decreased along the thickness direction, and grain refi nement was due to the combination of continuous, discontinuous, and geometric dynamic recrystallization. The tensile properties of the sliced samples were found to be uniform, and the ultimate tensile strength reached 62% of that of the base metal. The main strengthening mechanism of the Al–Zn–Mg–Cu alloy joints consists of precipitation strengthening. In addition, the η ` → η phase transition and grain coarsening in the heat-affected zone were found to be responsible for the fracture of the joints.
文摘The rigid-interface friction model is usually used in the nonlinear vibrationof the rectangular plate with dry friction support edges. The present study provides an extensionby using a hysteretic spring friction model and taking account of the stick-slip motion of theplate. Results for a range of problem parameters have been obtained. The results show that thenonlinear frequency response behavior of the system can be quite different from the rigid-interfacefriction model. The effects of the stiffness at friction interfaces and the stick-slip motion on thenonlinear vibration of the plate are significant and hence cannot be neglected.
文摘The effects on the local skin friction of smooth flat plate by formation of air cavity are investigated experimentally,under the conditions of several variations of air injection angle,pore size,porous surface area and transverse step.The experimental results show that local skin friction of downstream of the porous section could be reduced at extent ranging from 50% to 90%,by injection air through pore or slot,with free stream velocities from 2 to 6 m/s.The pore size and area of air injection surface have small effect on skin friction reduction,step has significant effect on skin friction reduction.The mechanism of the skin friction reduction is due to the formation of air cavity,mixed with air and water,between the flat plate and its water boundary layer.
基金funding from the Armament Research Board(ARMREB),Defence Research and Development Organization(DRDO),Ministry of Defence,Government of India (Grant no.:ARMREB/MAA/2018/200)。
文摘In this study, high velocity impact behaviour of friction stir welded AA7075-T651 25 mm thick plates were investigated using a 7.62 mm × 51 mm lead core and 7.62 mm × 39 mm steel core projectiles. Prior to ballistic trails, mechanical and metallurgical properties of friction stir welded AA 7075-T651 25 mm thick plates were studied. Microstructural and hardness studies revealed that friction stir welds constituted three distinct regions namely Weld Nugget(WN), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). Base Material(BM) and all three weld regions were ballistically tested as per military standard NIJ.0108.01 using lead and steel core bullets at maximum permissible velocities of 830 ± 20 and 700 ± 30 m/s, respectively. It has been found that base material(AA7075-T651)and all three weld regions of 25 mm thick plates were able to resist perforation by both types of projectiles used. However depth of penetration has been found to increase from BM to WN, HAZ and TMAZ for both types of projectiles. In all cases steel core projectiles caused higher depth of penetration compared to those caused by lead core projectiles. TMAZs of the friction stir welds were found to be the weakest zone. The fracture that occurred in the base material was spall fragmentation indicating brittle failure, whereas all zones of friction stir welded AA7075-T651 targets with a front petalling, indicating ductile failure. The post-ballistic tested samples showed no significant change in the microstructure of the BM and WN. On the other hand, TMAZ and HAZ showed severe grain deformation in the direction of projectile penetration, and the formation of adiabatic shear bands(ASB). This work showed that 25 mm thick friction stir welded AA7075-T651 joints responded well to ballistic impact loads, making them a good choice for light combat vehicles.
基金financial support provided by UGC-DAE-CSR (CSR-KN/CRS-04/201213/738) through fellowship
文摘Titanium tube and stainless steel tube plate were welded by an innovative friction welding of tube to tube plate using an external tool (FWTPET). Copper was used as an interlayer for joining the dissimilar materials and also to minimize the effect of intermetallics formed at the joint interface. The process parameters that govern FWTPET process are plunge rate, rotational speed, plunge depth, axial load and flash trap profile. Among them, the flash trap profile of the tube has a significant influence on the joint integrity. Various flash trap profiles like vertical slots, holes, zig-zag holes, and petals were made on the titanium tube welded to the stainless steel tube plate. Macroscopic and microscopic studies reveal defect-free joints. The presence of copper interlayer and intermetallics was evident from X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. The microhardness survey was presented across and along the interface. A novel test procedure called “plunge shear test” was developed to evaluate the joint properties of the welded joints. The highest shear fracture load of 31.58 kN was observed on the sample having petals as flash trap profile. The sheared surfaces were further characterized using SEM for fractography.
基金the Shanghai Automotive Industry Science and Technology Development Foundation(No.1614)
文摘We focus on the friction loss measurement and reduction of the timing belt guide plates of a fourcylinder gasoline engine. To minimize the friction loss caused by the dynamic friction of the guide plates during timing belt motion and improve the efficiency of the internal combustion engine(ICE), we adopt four different plastic materials in fabricating the guide plates. With controlled engine boundary conditions and operational modes, an AVL electric dynamometer is used to measure the output of the engine. The results indicate that selecting polytetrafluoroethylene(PTFE) as the additive in fabricating the guide plates can effectively reduce the friction loss, so that the output torque and output power of the engine can be improved, thus reducing fuel consumptions. This work also has positive impact on the efficiency optimization of similar ICEs.
文摘This study delves into both experimental and analytical examinations of heat exchange in a straight channel, where Al_(2)O_(3)-water nanofluids are utilized, spanning the Reynolds number spectrum from 100 to 1800. Diverse volume fractions(1%, 2%, and 3%) of Al_(2)O_(3)-water nanofluids are meticulously prepared and analyzed. The essential physical properties of these nanofluids, critical for evaluating their thermal and flow characteristics, have been comprehensively assessed. From a quantitative perspective, numerical simulations are employed to predict the Nusselt number(Nu) and friction factor(f). The empirical findings reveal intriguing trends: the friction factor experiences an upward trend with diminishing velocity, attributed to heightened molecular cohesion. Conversely, the friction factor demonstrates a decline with diminishing volume fractions, a consequence of reduced particle size. Both the nanofluid's viscosity and heat transfer coefficient exhibit a rise in tandem with augmented volume flow rate and concentration gradient. Notably, the simulation results harmonize remarkably well with experimental data. Rigorous validation against prior studies underscores the robust consistency of these outcomes. In the pursuit of augmenting heat transfer, a volume fraction of 3% emerges as particularly influential, yielding an impressive 53.8% enhancement. Minor increments in the friction factor, while present, prove negligible and can be safely overlooked.
基金National Natural Science Foundation of China(No.50475106)
文摘The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated.A three-dimensional Navier-Stokes(N-S)equation considering viscous force and inertial force rather than Reynolds equation or modified Reynolds equation is presented to model the flow field.Pressure and temperature distribution in radial and circumferential direction under three different conditions,i.e.,isothermal,that considering viscosity-temperature characteristic as well as shear thinning non-Newtonian fluid are simulated,respectively,by utilizing the commercial computational fluid dynamics(CFD)software FLUENT.The results reveal that the grooves on the driven plate make the pressure,temperature distribution present periodic variation.The oil temperature and shear rate have important effects on the flow field between frictional pairs,and the oil temperature is more important parameter.The simulation results lay a theoretical foundation for the reasonable designs ofhydroviscous drive.
基金This project is supported by National Natural Science Foundation of China(No.50075075) National "Ten-Five" Science and Technology Project of China(No.ZZ 01-13A-02-02-03). J
文摘The 3-D traction field in the pressure screw-pair of a 3 500 heavy and mediumplate mill press down system is successfully calculated by applying the 3-D frictional contactmultipole-BEM and the corresponding program that has been developed. The computing results show themedium diameter orientation is unreliable, especially under the interference of an outer forcecouple. Under such working conditions, the circumferential traction distribution on the screw teethis extremely uneven, which is the main reason for the destruction and short life time ofscrew-pairs. When utilizing the same precision (the relative tolerance is 10X10^(-5)), themultipole-BEM uses almost the same CPU time as used by the FEM, but the needed computer memory sizeis only one eightieth of that needed by the FEM (10 MB vs. 800 MB). The multipole-BEM is well suitedfor computing large-scale engineering problems.
基金supported by the National Natural Science Foundation of China(NSFC)(No.51265043 and 51265042)the Special Construction Project of Advanced Science and Technology Innovation Team of Jiangxi Province(No.20171BCB24007)
文摘In this study, 20 mm thick AA7075-T6 alloy plates were joined by friction stir welding. The microstructure and mechanical properties of the nugget zone along the thickness direction from the top to the bottom was investigated. The results showed that the microstructure including the grain size, the degree of dynamic recrystallization, the misorientation angle distribution and the precipitation phase containing its size, type and content exhibited a gradient distribution along the thickness direction. The testing results of mechanical properties of the slices showed that the nugget was gradually weakened along the depth from the top to the bottom. The maximum ultimate tensile strength, yield strength and elongation of the slice in the nugget top-middle are obtained, which are 415 MPa, 255 MPa and 8.1%, respectively.
基金This research was financially supported by the Major Project of National Natural Science Foundation of China(No.50235030)the National 973 Planning Project(No.G1999065009)+1 种基金the Science and Technology Cooperation Project between China and Poland Governments in 2002(No.2002M3)their supports are gratefully acknowledged.
文摘Ni-matrix composite coating containing AI2O3 nano-particles is prepared by brush plating. The effects of the nano-particles on the microstructure, microhardness and tribological properties of the composite coating under the lubrication of a diesel oil containing sand are investigated. The results show that the microstructure of the composite coating is finer than that of the pure nickel coating due to the codeposition of the nano-particles. When the nano-particle concentration in the electroplating bath reaches 20 g/L, the microhardness, and wear resistance of the composite coating is as much as 1.6 times and 1.3-2.5 times of those of the pure nickel coating respectively. The main hardening mechanism of the composite coating is superfine crystal grain strengthening and dispersion strengthening. The composite coating is characterized by scuffing as it slides against Si3N4 under the present test conditions.
基金Project(2021YFB3400903) supported by the National Key R&D Program of ChinaProject(1053320211480) supported by the Science and Technology Innovation Project of Graduate Students of Central South University,China。
文摘Creep ageing forming(CAF)has been widely used in the aerospace engineering,but how to optimize the processing conditions,especially under complex stress state of the CAF process for large-size components produced by friction-stir welding is still a great challenge to now.In this work,the creep ageing behaviors and underlying microstructure evolution of a thick friction-stir welded Al-Cu alloy plate after CAF process under different stress levels are systematically investigated.The creep strain and the strength of the joint are both significantly increased when the stress is close to the average yield strength of the initial weld joint.The grain size reduces while the local strain and dislocation density increase from top to bottom of the NZ;hence,the bottom layer of the weld joint exhibits higher creep strain and steady-stage creep strain rate during the CAF process.The results reveal that the gradient microstructures sensitive to the stress level effectively govern the creep-ageing performance from the upper to the bottom layer in a thick friction stir welded Al-Cu alloy plate.Rationally increasing the initial dislocation density of the weld joint can both enhance the tensile properties and promote the creep deformation of the weld joint for CAF process.
文摘An analysis is performed to study the magnetohydrodynamic flow of an electrically conducting, viscous incompressible fluid past a semi-infinite vertical plate with variable surface temperature under the action of transversely applied magnetic field. The heat due to viscous dissipation and the induced magnetic field are assumed to be negligible. The dimensionless governing equations are unsteady, two-dimensional, coupled and non-linear governing equations. It is found that the magnetic field parameter has a retarding effect on the velocities of air and water.
