Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restr...Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restricting widespread use.In this study,ultra-fine-grained and homogeneous Mg alloys were fabricated using double-sided friction stir processing(DS-FSP)with liquid CO_(2) rapid cooling,leading to a significant enhancement in the strength-ductility synergy of the stirred zone.The results demonstrate that DS-FSP samples exhibit simultaneous improvements in ultimate tensile strength(UTS)and elongation,reaching 334.1±15 MPa and 28.2±7.3%,respectively.Compared to the non-uniform fine-grained microstructure obtained through single-sided friction stir processing,DS-FSP generates a uniform ultra-fine-grained structure,fundamentally altering the fracture behavior and mechanisms of Mg alloys.The DS-FSP samples exhibit irregular fracture patterns due to variations in basal slip system activation among different grains.In contrast,single-sided friction stir processing samples,characterized by a fine-grained yet heterogeneous microstructure,display flat shear fractures dominated by high-density dislocation initiation induced by twin formation,with fracture propagation dictated by the non-uniform texture.By achieving an ultra-fine grain size and homogeneous texture,DS-FSP effectively modifies the fracture mechanisms,thereby enhancing the strength-ductility balance of bio-magnesium alloys.展开更多
The double-sided lapping process is extensively employed in the manufacturing of wafers,optical windows,and seal rings due to its high efficiency and ability to achieve precise flatness.However,limited research has ex...The double-sided lapping process is extensively employed in the manufacturing of wafers,optical windows,and seal rings due to its high efficiency and ability to achieve precise flatness.However,limited research has explored the thickness uniformity among different workpieces after double-sided lapping,and the underlying mechanism remains unclear.To address the demand for higher precision,this paper first analyzed the relative kinematic model between the workpiece and the lapping plate to clarify the causes of thickness variations among workpieces after double-sided lapping.Subsequently,a finite element method(FEM)model was developed to account for the pressure distribution on the workpiece surfaces at the initial stage of the process.The results indicate that the number of workpieces influences the final thickness variation.Then,various sets of thin copper plates with different thicknesses were lapped,and the findings revealed that five copper plates processed simultaneously exhibited more uniform thickness compared to the three plates.The experimental results align well with the theoretical analysis.Ultimately,a thickness variation of less than 6μm was achieved on five copper plates measuringΦ100×2.9 mm.This study presents a comprehensive analysis of the mechanisms influencing thickness uniformity in the double-sided lapping process and provides practical guidelines for optimizing the process to achieve stringent precision standards in industrial applications.展开更多
The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as th...The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.展开更多
The microstructure evolution in the weld zone of double-side friction stir welded（DS-FSWed） 7085-T7452 Al alloy was investigated by the electron backscatter diffraction method.The results indicate that DS-FSW proces...The microstructure evolution in the weld zone of double-side friction stir welded（DS-FSWed） 7085-T7452 Al alloy was investigated by the electron backscatter diffraction method.The results indicate that DS-FSW process results in substantial grain refinement.The misorientation angle distribution shows a very high volume fraction of high angle grain boundary（HAGB）（above 75%） under DS-FSW condition at rotational rate of 300 r/min.The fraction of HAGB rapidly decreases with increasing the rotational rate from 300 to 950 r/min,and the obvious growth of grain in the weld nugget zone（WNZ） is presented.The average grain sizes in the elongated grains of thermal-mechanical affected zone（TMAZ） and partially equiaxed and coarser grains of thermal affected zone（HAZ） are 7.3 and 15.7 μm with the fractions of HAGBs less than 43% and 30%,respectively.The intensities of（100）,（110） and（111） pole figures in the WNZ obviously decrease when compared with those in the BM and present significantly difference along the thickness direction of plate.展开更多
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
Double-side probeless friction stir spot welding (DP-FSSW) of AA2198 alloy was conducted to investigate the microstructure and mechanical properties. Compared with common single-side probeless friction stir spot weldi...Double-side probeless friction stir spot welding (DP-FSSW) of AA2198 alloy was conducted to investigate the microstructure and mechanical properties. Compared with common single-side probeless friction stir spot welding (P-FSSW), the plastic strain during DP-FSSW is nearly symmetrical with respect to the bondline to suppress the extension of hook defect, which is detrimental to the joint mechanical strength. With DP-FSSW, a fully metallurgically bonded region has formed due to severe plastic deformation at high temperatures. Tensile/shear tests show that the joint strength could exceed 8 kN, which is comparable to P-FSSW and refill FSSW, and all fractures happen in a shear failure mode as cracks extend along the in terface of two sheets. The microhard ness profile exhibits a uniform distribution along the thick ness direction, in which the hook defect shows the lowest value.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
A double-sided silicon strip detector(DSSD)with active area of 48 mm x 48 mm and thickness of300μm has been developed. Each side of DSSD consists of48 strips, each with width of 0.9 mm and inter-strip separation of 0...A double-sided silicon strip detector(DSSD)with active area of 48 mm x 48 mm and thickness of300μm has been developed. Each side of DSSD consists of48 strips, each with width of 0.9 mm and inter-strip separation of 0.1 mm. Electrical properties and detection performances including full depletion bias voltage, reverse leakage current, rise time, energy resolution and cross talk have been studied. At a bias of 80 V, leakage current in each strip is less than 15 nA, and rise time for alpha particle at 5157 keV is approximately 15 ns on both sides.Good energy resolutions have been achieved with0.65-0.80% for the junction strips and 0.85-1.00% for the ohmic strips. The cross talk is found to be negligible on both sides. The overall good performance of DSSD indicates its readiness for various nuclear physics experiments.展开更多
In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is gr...In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.展开更多
Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corros...Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al4.5FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al0.5Fe3Si0.5 was observed in the backside. The formation of reinforcing phases of Al-Fe-Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.展开更多
Friction stir welding (FSW) of aluminum alloys is currently utilized in several modern industries. The joints must have sufficient elastic?plastic response and formability levels similar to that of the base metal. In ...Friction stir welding (FSW) of aluminum alloys is currently utilized in several modern industries. The joints must have sufficient elastic?plastic response and formability levels similar to that of the base metal. In this work, double-sided FSW of AA6061 sheet was compared with its conventional single-sided one. An adjustable tool with different pin lengths (50%?95% of the sheet thickness) was used to perform the double-sided welds. Macro- and micro-structures, strength, and hardness of the joints were investigated to determine the optimum pin penetration depth. The best results were obtained for a double-sided joint made by a pin length equal to 65% of the sheet thickness, which showed an increase of 41% in the ultimate tensile strength compared with the single-sided joint.展开更多
In the proposed method, the current/arc is guided through the keyhole so that the energy of the plasma jet is compensated while it is consumed in heating the workpiece along the keyhole. As a result, deep narrow penet...In the proposed method, the current/arc is guided through the keyhole so that the energy of the plasma jet is compensated while it is consumed in heating the workpiece along the keyhole. As a result, deep narrow penetration has been achieved on 12.7 mm (1/2') thick stainless steel plates using 70 A welding current.展开更多
Double-sided lapping is an precision machining method capable of obtaining high-precision surface.However,during the lapping process of thin pure copper substrate,the workpiece will be warped due to the influence of r...Double-sided lapping is an precision machining method capable of obtaining high-precision surface.However,during the lapping process of thin pure copper substrate,the workpiece will be warped due to the influence of residual stress,including the machining stress and initial residual stress,which will deteriorate the flatness of the workpiece and ultimately affect the performance of components.In this study,finite element method(FEM)was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping.Considering the initial residual stress of the workpiece,the stress caused by the lapping and their distribution characteristics,a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters.The results showed that the primary cause of the warping deformation of the workpiece in the doublesided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces.The finite element simulation results were in good agreement with the experimental results.展开更多
The double-sided incremental forming(DSIF)improved the process flexibility compared to other incremental sheet forming(ISF)processes.Despite the flexible nature,it faces the challenge of low geometric precision like I...The double-sided incremental forming(DSIF)improved the process flexibility compared to other incremental sheet forming(ISF)processes.Despite the flexible nature,it faces the challenge of low geometric precision like ISF variants.In this work,two strategies are used to overcome this.First,a novel method is employed to determine the optimal support tool location for improving geometric precision.In this method,the toolpath oriented the tools to each other systematically in the circumferential direction.Besides,it squeezed the sheet by the same amount at the point of interest.The impacts of various support tool positions in the circumferential direction are evaluated for geometric precision.The results demonstrate that the support tool should support the master tool within 10°to its local normal in the circumferential direction to improve the geometric accuracy.Second,a two-stage process reduced the geometric error of the part by incrementally accommodating the springback error by artificially increasing the step size for the second stage.With the optimal support tool position and two-stage DSIF,the geometric precision of the part has improved significantly.The proposed method is compared to the best DSIF toolpath strategies for geometric accuracy,surface roughness,forming time,and sheet thickness fluctuations using grey relational analysis(GRA).It outperforms the other toolpath strategies including single-stage DSIF,accumulative double-sided incremental forming(ADSIF),and two-stage mixed double sided incre-mental forming(MDSIF).Our approach can improve geometric precision in complex parts by successfully employing the support tool and managing the springback incrementally.展开更多
We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens-Fresnel diffraction integral method. This theoretical model i...We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens-Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.展开更多
A series of laser-TIG double-side welding experiments for aluminum alloys were carried out to investigate the heat efficiency of the process. The melting efficiency was introduced to evaluate quantitatively the degree...A series of laser-TIG double-side welding experiments for aluminum alloys were carried out to investigate the heat efficiency of the process. The melting efficiency was introduced to evaluate quantitatively the degree of the mutual effect of the laser and the arc. The results showed that the melting efficiency of laser-TIG double-side welding exceeded the sum of the laser and the arc taken separately. With the increase of heat input, the weld depth and melting efficiency of the laser and the arc were increased signifwantly. This, in fact, implies the strong mutual effect of the laser and the arc as heat sources joined simultaneously in the process. Comparatively, the higher efficiency of the laser constituent of heat sources plays the main role in the increase of the process efficiency. The phenomena of arc column convergence, increased laser absorptivity and the formation of heat accumulation region are the causes of the improvement of heat efficiency.展开更多
Currently,conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys,and its application to thick plates is still challenging in terms of welding efficiency and joint ...Currently,conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys,and its application to thick plates is still challenging in terms of welding efficiency and joint mechanical properties.Simultaneous double-sided friction stir welding(SDS-FSW)is a high-efficiency joining technique specifically developed for welding thick plates.However,there is little research on the influence of SDS-FSW process parameters on the joint mechanical properties.In this study,a 12 mm thick AA6061-T6 aluminum alloy and dual robot welding equipment are used to conduct SDS-FSW experiments exploring the influence of rotational speedωand welding speed v on the mechanical properties and microstructure.The results show that when the welding parameters areω=800 r/min and v=60–80 mm/min,smooth and defect-free thick plate aluminum alloy SDS-FSW joints can be obtained,and the macroscopic morphology of the joints is distributed in a“dumbbell”shape.The grain size in the weld nugget zone increases with increasing welding heat input.The microhardness distribution in the joint displays a“W”shape,and the hardness value of the weld nugget zone can reach 67%to 86%of that of the base metal(BM).The junction between the thermo-mechanically affected zone and the heat affected zone is the weakest region of the joint,with the lowest hardness being approximately 51%of that of the BM.When the welding parameters areω=800 r/min and v=140 mm/min,the SDS-FSW joint has the highest tensile strength,reaching 78.43%of the BM strength and exhibiting ductile fracture characteristics.This research indicates that acceptable weld strength in thick aluminum alloys can be achieved via the SDS-FSW joining mechanism,highlighting its significant potential for industrial applications.展开更多
Up till now, most of the researchers believe that there are four kinds of forces in the weld pool convection, they aresurface tension, electromagnetic force, buoyancy and gas shear stress. So electromagnetic force is ...Up till now, most of the researchers believe that there are four kinds of forces in the weld pool convection, they aresurface tension, electromagnetic force, buoyancy and gas shear stress. So electromagnetic force is very important,especially when large current is applied. In most of previous models, the electromagnetic force is calculated analytically,in which only the axial component of current is considered. Actually the radial component of current has thesame effect, and may be advanced in some locations. In double-sided arc welding process, instead of the earthclamp, another torch is placed on the opposite side; the current will go from one torch, through the weld zone,to another torch. In this case, the current is more concentrated in the weld zone; the electromagnetic force willhave significant effect compared with conventional welding process. In this paper, a new method of numericalcalculation for electromagnetic force is developed, in which both axial and radial components are considered. And asan example, the distribution of electromagnetic force in double-sided arc welding is calculated. It demonstrates thatthis new method could give more accurate simulation of electromagnetic force, and is close to the actual process.展开更多
We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current(DC)voltage.The discharge tests show that sliding discharge and...We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current(DC)voltage.The discharge tests show that sliding discharge and extended discharge are filamentary discharge.The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle,ultimately expands the discharge channel.The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge(DBD).The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge,which causes a bulge structure in the discharge channel.The bias DC electrode can deflect the direction of the induced jet,then modifying the properties of the boundary layer.Extended discharge can accelerate the velocity of the starting vortex,improving the horizontal velocity profile by 203%.The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate,compared with sliding discharge and DBD.However,the momentum growth of sliding discharge lasts longer in the whole pulsed cycle,indicating that sliding discharge can also inject more momentum.展开更多
In this paper, we report a continuous deposition method for double-sided CeO2/YSZ/Y2O3 buffer layers by reel-to-reel in a D.C. magnetron reactive sputtering system. X-ray diffraction exhibited all the samples were hig...In this paper, we report a continuous deposition method for double-sided CeO2/YSZ/Y2O3 buffer layers by reel-to-reel in a D.C. magnetron reactive sputtering system. X-ray diffraction exhibited all the samples were highly c-axis oriented and atomic force microscope observations revealed a smooth, dense and crack-free surface morphology. Out-of-plane, in-plane texture, and surface roughness of multi-buffer layers were improved under optimized deposition conditions. Full width at half maximum (FWHM) values of out-of-plane and in-plane were about 4° and 5.5° in 50 cm double-sided buffed template. YBa2Cu3O7-δ films with thickness of 1.2 μm were deposited on both sides of the buffed tape. Both sides showed similar critical current density, Jc (77 K, self field) as 0.8 MA/cm2 and 0.7 MA/cm2, respectively.展开更多
基金financial support from the National Key Research and Development Program of China(2021YFC2400703)Zhengzhou City Major Special Project for Collaborative InnovationChina Scholarship Council。
文摘Bio-magnesium(Mg)alloys exhibit excellent biocompatibility and biodegradability,making them highly promising for implant applications.However,their limited strength-ductility balance remains a critical challenge restricting widespread use.In this study,ultra-fine-grained and homogeneous Mg alloys were fabricated using double-sided friction stir processing(DS-FSP)with liquid CO_(2) rapid cooling,leading to a significant enhancement in the strength-ductility synergy of the stirred zone.The results demonstrate that DS-FSP samples exhibit simultaneous improvements in ultimate tensile strength(UTS)and elongation,reaching 334.1±15 MPa and 28.2±7.3%,respectively.Compared to the non-uniform fine-grained microstructure obtained through single-sided friction stir processing,DS-FSP generates a uniform ultra-fine-grained structure,fundamentally altering the fracture behavior and mechanisms of Mg alloys.The DS-FSP samples exhibit irregular fracture patterns due to variations in basal slip system activation among different grains.In contrast,single-sided friction stir processing samples,characterized by a fine-grained yet heterogeneous microstructure,display flat shear fractures dominated by high-density dislocation initiation induced by twin formation,with fracture propagation dictated by the non-uniform texture.By achieving an ultra-fine grain size and homogeneous texture,DS-FSP effectively modifies the fracture mechanisms,thereby enhancing the strength-ductility balance of bio-magnesium alloys.
基金Supported by the Liaoning Provincial Natural Science Foundation(Grant No.2023-MSBA-008)Unveiling and Commanding Program of Liaoning Province(Grant No.2022JH1/10800080)the Fundamental Research Funds for the Central Universities(Grant No.DUT24MS008).
文摘The double-sided lapping process is extensively employed in the manufacturing of wafers,optical windows,and seal rings due to its high efficiency and ability to achieve precise flatness.However,limited research has explored the thickness uniformity among different workpieces after double-sided lapping,and the underlying mechanism remains unclear.To address the demand for higher precision,this paper first analyzed the relative kinematic model between the workpiece and the lapping plate to clarify the causes of thickness variations among workpieces after double-sided lapping.Subsequently,a finite element method(FEM)model was developed to account for the pressure distribution on the workpiece surfaces at the initial stage of the process.The results indicate that the number of workpieces influences the final thickness variation.Then,various sets of thin copper plates with different thicknesses were lapped,and the findings revealed that five copper plates processed simultaneously exhibited more uniform thickness compared to the three plates.The experimental results align well with the theoretical analysis.Ultimately,a thickness variation of less than 6μm was achieved on five copper plates measuringΦ100×2.9 mm.This study presents a comprehensive analysis of the mechanisms influencing thickness uniformity in the double-sided lapping process and provides practical guidelines for optimizing the process to achieve stringent precision standards in industrial applications.
基金Project supported by Science and Technology on Power Beam Processes Laboratory at Beijing Aeronautical Manufacturing Technology Research Institute,China
文摘The T-joints of Ti?6Al?4V alloy were manufactured by double-sided synchronized laser beam welding with the homologous filler wire. The formation, microstructure and mechanical properties of welded joints as well as the correlations of each other were investigated. The results indicate that the quality of weld seams is good without defects such as discontinuity, beading, visible cracks or porosity, which is linked to the steady molten pool behavior and droplet transition. The morphologies of the heat affected zone (HAZ) located on the skin and stringer are disparate. The microstructure of the HAZ and fusion zone (FZ) is mainly comprised of acicular martensiticα′ phases. The microhardness of the HAZ and FZ is higher than that of the base metal (BM) and reaches a maximum value at the HAZ near FZ on the stringer. The tensile specimens along the skin and stringer fractured at the BM with ductile fracture surfaces.
基金Project(51405392)supported by the National Natural Science Foundation of ChinaProject(20136102120022)supported by the Research Fund for the Doctoral Program of Higher Education of China+1 种基金Project(2013JQ6001)supported by the Natural Science Foundation of Shaanxi Province,ChinaProject(3102015ZY023)supported by the Fundamental Research Funds for the Central Universities,China
文摘The microstructure evolution in the weld zone of double-side friction stir welded（DS-FSWed） 7085-T7452 Al alloy was investigated by the electron backscatter diffraction method.The results indicate that DS-FSW process results in substantial grain refinement.The misorientation angle distribution shows a very high volume fraction of high angle grain boundary（HAGB）（above 75%） under DS-FSW condition at rotational rate of 300 r/min.The fraction of HAGB rapidly decreases with increasing the rotational rate from 300 to 950 r/min,and the obvious growth of grain in the weld nugget zone（WNZ） is presented.The average grain sizes in the elongated grains of thermal-mechanical affected zone（TMAZ） and partially equiaxed and coarser grains of thermal affected zone（HAZ） are 7.3 and 15.7 μm with the fractions of HAGBs less than 43% and 30%,respectively.The intensities of（100）,（110） and（111） pole figures in the WNZ obviously decrease when compared with those in the BM and present significantly difference along the thickness direction of plate.
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.
基金financially supported by the National Natural Science Foundation of China (No. 51574196)the Aeronautical Science Foundation of China (No. 20161125002)the “111 Project” (No. B08040)
文摘Double-side probeless friction stir spot welding (DP-FSSW) of AA2198 alloy was conducted to investigate the microstructure and mechanical properties. Compared with common single-side probeless friction stir spot welding (P-FSSW), the plastic strain during DP-FSSW is nearly symmetrical with respect to the bondline to suppress the extension of hook defect, which is detrimental to the joint mechanical strength. With DP-FSSW, a fully metallurgically bonded region has formed due to severe plastic deformation at high temperatures. Tensile/shear tests show that the joint strength could exceed 8 kN, which is comparable to P-FSSW and refill FSSW, and all fractures happen in a shear failure mode as cracks extend along the in terface of two sheets. The microhard ness profile exhibits a uniform distribution along the thick ness direction, in which the hook defect shows the lowest value.
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supported by the National Natural Science Foundation of China(Nos.U1432246,U1632136,U1432127,11375268,11635015,and 11475263)the National Basic Research Program of China(No.2013CB834404)
文摘A double-sided silicon strip detector(DSSD)with active area of 48 mm x 48 mm and thickness of300μm has been developed. Each side of DSSD consists of48 strips, each with width of 0.9 mm and inter-strip separation of 0.1 mm. Electrical properties and detection performances including full depletion bias voltage, reverse leakage current, rise time, energy resolution and cross talk have been studied. At a bias of 80 V, leakage current in each strip is less than 15 nA, and rise time for alpha particle at 5157 keV is approximately 15 ns on both sides.Good energy resolutions have been achieved with0.65-0.80% for the junction strips and 0.85-1.00% for the ohmic strips. The cross talk is found to be negligible on both sides. The overall good performance of DSSD indicates its readiness for various nuclear physics experiments.
基金The authors wish to express their gratitude to the financial support to this project from the project foundation of the National Key Laboratory of Advanced Welding Production Technology of Harbin Institute of Technology and the US National Science Foundation under grant No.DMI 9812981
文摘In the double-sided arc welding system (DSAW) composing of PAW+TIG arcs, the PAW arc is guided by the TIG arc so that the current mostly flows through the direction of the workpiece thickness and the penetration is greatly improved. To analyze the current density distribution in DSAW is beneficial to understanding of this process. Considering all kinds of dynamic factors acting on the weldpool, this paper discusses firstly the surface deformation of the weldpool and the keyhole formation in PAW+TIG DSAW process on the basis of the magnetohydrodynamic theory and variation principles. Hence, a model of the current density distribution is developed. Through numerical simulation, the current density distribution in PAW+TIG DSAW process is quantitatively analyzed. It shows that the minimal radius of keyhole formed in PAW+TIG DSAW process is 0.5 mm and 89.5 percent of current flows through the keyhole.
基金financially supported by the National Natural Science Foundation of China(No.51005049)
文摘Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al-Si filler wire to investigate the effect of Al-Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al4.5FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al0.5Fe3Si0.5 was observed in the backside. The formation of reinforcing phases of Al-Fe-Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.
基金The support of Iran National Science Foundation (INSF) (Grant No. 91051732)
文摘Friction stir welding (FSW) of aluminum alloys is currently utilized in several modern industries. The joints must have sufficient elastic?plastic response and formability levels similar to that of the base metal. In this work, double-sided FSW of AA6061 sheet was compared with its conventional single-sided one. An adjustable tool with different pin lengths (50%?95% of the sheet thickness) was used to perform the double-sided welds. Macro- and micro-structures, strength, and hardness of the joints were investigated to determine the optimum pin penetration depth. The best results were obtained for a double-sided joint made by a pin length equal to 65% of the sheet thickness, which showed an increase of 41% in the ultimate tensile strength compared with the single-sided joint.
基金This work is supported by the National Natural Science Foundation under Grant DMI-9812981
文摘In the proposed method, the current/arc is guided through the keyhole so that the energy of the plasma jet is compensated while it is consumed in heating the workpiece along the keyhole. As a result, deep narrow penetration has been achieved on 12.7 mm (1/2') thick stainless steel plates using 70 A welding current.
基金National Key Research and Development Program of China(Grant No.2018YFA0702900)Science Challenge Project of China(Grant No.TZ2016006)National Natural Science Foundation of China(Grant No.51975096)。
文摘Double-sided lapping is an precision machining method capable of obtaining high-precision surface.However,during the lapping process of thin pure copper substrate,the workpiece will be warped due to the influence of residual stress,including the machining stress and initial residual stress,which will deteriorate the flatness of the workpiece and ultimately affect the performance of components.In this study,finite element method(FEM)was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping.Considering the initial residual stress of the workpiece,the stress caused by the lapping and their distribution characteristics,a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters.The results showed that the primary cause of the warping deformation of the workpiece in the doublesided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces.The finite element simulation results were in good agreement with the experimental results.
基金supported by the National Natural Science Foun-dation of China(Nos.52075025,51975328)Project funded by China Postdoctoral Science Foundation(No.2021T140418)。
文摘The double-sided incremental forming(DSIF)improved the process flexibility compared to other incremental sheet forming(ISF)processes.Despite the flexible nature,it faces the challenge of low geometric precision like ISF variants.In this work,two strategies are used to overcome this.First,a novel method is employed to determine the optimal support tool location for improving geometric precision.In this method,the toolpath oriented the tools to each other systematically in the circumferential direction.Besides,it squeezed the sheet by the same amount at the point of interest.The impacts of various support tool positions in the circumferential direction are evaluated for geometric precision.The results demonstrate that the support tool should support the master tool within 10°to its local normal in the circumferential direction to improve the geometric accuracy.Second,a two-stage process reduced the geometric error of the part by incrementally accommodating the springback error by artificially increasing the step size for the second stage.With the optimal support tool position and two-stage DSIF,the geometric precision of the part has improved significantly.The proposed method is compared to the best DSIF toolpath strategies for geometric accuracy,surface roughness,forming time,and sheet thickness fluctuations using grey relational analysis(GRA).It outperforms the other toolpath strategies including single-stage DSIF,accumulative double-sided incremental forming(ADSIF),and two-stage mixed double sided incre-mental forming(MDSIF).Our approach can improve geometric precision in complex parts by successfully employing the support tool and managing the springback incrementally.
基金Project supported by the Natural National Science Foundation of China （Grant Nos 20131040 and 50172013）, the Heilongjiang Province Science Foundation （Grant No F2004-8）, and the 0utstanding Young Research Foundation of Heilongjiang University （Grant No JC200307）.
文摘We present a theoretical model to analyse the propagation of a Gaussian laser beam through double-sided nonlinear media. This model is based on the Huygens-Fresnel diffraction integral method. This theoretical model is not only consistent with the cascade structure model for a small nonlinear phase-shift but also can be used for a large nonlinear phase-shift. It has been verified that it is suitable to characterize the double-sided nonlinear media compared with the cascade structure model. A good agreement between the experimental data and the results from the theoretical model is obtained. It will be useful for the design of multi-sided nonlinear materials.
文摘A series of laser-TIG double-side welding experiments for aluminum alloys were carried out to investigate the heat efficiency of the process. The melting efficiency was introduced to evaluate quantitatively the degree of the mutual effect of the laser and the arc. The results showed that the melting efficiency of laser-TIG double-side welding exceeded the sum of the laser and the arc taken separately. With the increase of heat input, the weld depth and melting efficiency of the laser and the arc were increased signifwantly. This, in fact, implies the strong mutual effect of the laser and the arc as heat sources joined simultaneously in the process. Comparatively, the higher efficiency of the laser constituent of heat sources plays the main role in the increase of the process efficiency. The phenomena of arc column convergence, increased laser absorptivity and the formation of heat accumulation region are the causes of the improvement of heat efficiency.
基金Supported by National Key R&D program of China(Grant No.2019YFA0709004)。
文摘Currently,conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys,and its application to thick plates is still challenging in terms of welding efficiency and joint mechanical properties.Simultaneous double-sided friction stir welding(SDS-FSW)is a high-efficiency joining technique specifically developed for welding thick plates.However,there is little research on the influence of SDS-FSW process parameters on the joint mechanical properties.In this study,a 12 mm thick AA6061-T6 aluminum alloy and dual robot welding equipment are used to conduct SDS-FSW experiments exploring the influence of rotational speedωand welding speed v on the mechanical properties and microstructure.The results show that when the welding parameters areω=800 r/min and v=60–80 mm/min,smooth and defect-free thick plate aluminum alloy SDS-FSW joints can be obtained,and the macroscopic morphology of the joints is distributed in a“dumbbell”shape.The grain size in the weld nugget zone increases with increasing welding heat input.The microhardness distribution in the joint displays a“W”shape,and the hardness value of the weld nugget zone can reach 67%to 86%of that of the base metal(BM).The junction between the thermo-mechanically affected zone and the heat affected zone is the weakest region of the joint,with the lowest hardness being approximately 51%of that of the BM.When the welding parameters areω=800 r/min and v=140 mm/min,the SDS-FSW joint has the highest tensile strength,reaching 78.43%of the BM strength and exhibiting ductile fracture characteristics.This research indicates that acceptable weld strength in thick aluminum alloys can be achieved via the SDS-FSW joining mechanism,highlighting its significant potential for industrial applications.
文摘Up till now, most of the researchers believe that there are four kinds of forces in the weld pool convection, they aresurface tension, electromagnetic force, buoyancy and gas shear stress. So electromagnetic force is very important,especially when large current is applied. In most of previous models, the electromagnetic force is calculated analytically,in which only the axial component of current is considered. Actually the radial component of current has thesame effect, and may be advanced in some locations. In double-sided arc welding process, instead of the earthclamp, another torch is placed on the opposite side; the current will go from one torch, through the weld zone,to another torch. In this case, the current is more concentrated in the weld zone; the electromagnetic force willhave significant effect compared with conventional welding process. In this paper, a new method of numericalcalculation for electromagnetic force is developed, in which both axial and radial components are considered. And asan example, the distribution of electromagnetic force in double-sided arc welding is calculated. It demonstrates thatthis new method could give more accurate simulation of electromagnetic force, and is close to the actual process.
基金National Natural Science Foundation of China(Grant Nos.51607188,51790511,and 51906254)the Foundation for Key Laboratories of National Defense Science and Technology of China(Grant No.614220202011801).
文摘We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current(DC)voltage.The discharge tests show that sliding discharge and extended discharge are filamentary discharge.The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle,ultimately expands the discharge channel.The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge(DBD).The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge,which causes a bulge structure in the discharge channel.The bias DC electrode can deflect the direction of the induced jet,then modifying the properties of the boundary layer.Extended discharge can accelerate the velocity of the starting vortex,improving the horizontal velocity profile by 203%.The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate,compared with sliding discharge and DBD.However,the momentum growth of sliding discharge lasts longer in the whole pulsed cycle,indicating that sliding discharge can also inject more momentum.
文摘In this paper, we report a continuous deposition method for double-sided CeO2/YSZ/Y2O3 buffer layers by reel-to-reel in a D.C. magnetron reactive sputtering system. X-ray diffraction exhibited all the samples were highly c-axis oriented and atomic force microscope observations revealed a smooth, dense and crack-free surface morphology. Out-of-plane, in-plane texture, and surface roughness of multi-buffer layers were improved under optimized deposition conditions. Full width at half maximum (FWHM) values of out-of-plane and in-plane were about 4° and 5.5° in 50 cm double-sided buffed template. YBa2Cu3O7-δ films with thickness of 1.2 μm were deposited on both sides of the buffed tape. Both sides showed similar critical current density, Jc (77 K, self field) as 0.8 MA/cm2 and 0.7 MA/cm2, respectively.
