Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer(CMT)modes.Direct current CMT(DC-CMT)mode was used for Ti alloy deposition,and DC-CMT or CMT ...Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer(CMT)modes.Direct current CMT(DC-CMT)mode was used for Ti alloy deposition,and DC-CMT or CMT plus pulse(CMT+P)mode was used for the Al alloy deposition.During deposition of the first Al alloy layer,little and a significant amount of Ti alloy were melted using DC-CMT and CMT+P mode,respectively.TiAl_(3)formed in the reaction layer when DC-CMT mode was used,while TiAl_(3),TiAl,and Ti3Al formed in the reaction layer when CMT+P mode was used.Compared to using DC-CMT mode,more cracks occurred when using CMT+P.The nanohardness of the reaction layer was between that of the Al and Ti alloys,irrespective of the CMT modes.The average tensile strengths of the samples using DC-CMT and CMT+P mode were 108 MPa and 24 MPa,respectively.DC-CMT mode was more suitable for the wire and arc additive manufacturing of Ti/Al dissimilar alloys.展开更多
Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth...Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth rate tests.For evaluation of fatigue crack growth rate,three points bending specimens were used.The correlation between the range of stress intensity factor and crack growth rate was determined in different zones of the annealed weld joint.Fatigue crack growth rates were obviously different in different zones of weld joint of dissimilar titanium alloys,due to their different microstructures.Scanning electron microscope examinations were conducted on the fracture surface in order to determine the relevant fracture mechanisms and crack growth mechanisms with respect to the details of microstructure.展开更多
In this research project,copper and stainless steel were connected by two laser welding methods:straight seam welding and swing welding.Then,electronic tensile test machine,X-ray diffractometer,scanning electron micro...In this research project,copper and stainless steel were connected by two laser welding methods:straight seam welding and swing welding.Then,electronic tensile test machine,X-ray diffractometer,scanning electron microscope and metallographic microscope were used to analyze the tensile properties,macroscopic and microscopic structure morphology and phase of the welded joint.Based on the experimental results,we determined that the strength of the straight seam welded joint was higher.Because of the intermetallic compound near the weld in the swing welding process,it leads to stress concentration,crack cracking and strength reduction.In addition,the oscillating laser beam also leads to the disorderly direction of columnar crystal and coarse structure,which makes the joint strength decrease.展开更多
This study focuses on the bonding interface characteristics and mechanical properties of the bobbin tool friction stir welded dissimilar AA6056 and AA2219 aluminum alloy joints using diff erent welding speeds.Voids ar...This study focuses on the bonding interface characteristics and mechanical properties of the bobbin tool friction stir welded dissimilar AA6056 and AA2219 aluminum alloy joints using diff erent welding speeds.Voids arise solely in the stir zone at the AA2219 side.A distinct boundary with limited material mixing develops at the middle section of the bonding interface,while excellent material mixing with an irregularly jagged pattern forms at the top and bottom sections of the bonding interface.Increasing the welding speed,the material mixing is rarely changed at the middle section in comparison with the bottom section.Furthermore,a small diff erence between Guinier–Preston dissolution and Q phase precipitation leads to rare change of hardness in the heat aff ected zone(HAZ)at the AA6056 side.The increased hardness of the HAZ at the AA2219 side is attributed to avoidance of the dissolution ofθ’’phase precipitates.A maximum tensile strength of 181 MPa is obtained at 300 mm min-1.Fractures occur at the AA6056 side near the top and bottom surfaces and at the bonding interface in the middle section of the joints.The regions close to the top and bottom surfaces of the joints show a better ductility.展开更多
Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy exa...Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy examinations to characterize the precipitates required to assess internal stresses.Electron backscatter diffraction was employed to observe the inhomogeneous microstructures of the FSWed joints.Strain localization appeared in the heat affected zone(HAZ)of AA2024 side.After cyclic deformation of 500 cycles at a total strain amplitude of 0.5%,the strength of the dissimilar joints resumed basically to that of AA2024 base material.And the AA2024 HAZ was obviously hardened,which should be attributed to the introduced dislocations during cyclic deformation process.Cyclic hardening capacity of the joints increased with decreasing strain rate.展开更多
The microstructure and mechanical properties of pulse metal inert-gas (MIG) welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength ...The microstructure and mechanical properties of pulse metal inert-gas (MIG) welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength of the joints reached 235 MPa, which is 83% of that of 6061 aluminum alloy, and then decreased with the increase of travel speed while keeping other welding parameters constant. The microstructure, composition and fractography of joints were examined by the optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Grain boundary liquation and segregation occurred in the partially melted zone (PMZ) on 6061 aluminum alloy side, and brittle Fe-rich phases were observed in partially melted zone on A356 aluminum alloy side. The minimum microhardness appeared in heat-affected zone (HAZ) near A356 aluminum alloy substrate. The samples during tensile test failed mainly in PMZ and HAZ on A356 aluminum alloy side through mixed fracture mode with quasi cleavage and dimples on fracture surface.展开更多
Friction stir welding(FSW) was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed...Friction stir welding(FSW) was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β' phases can be observed at the heat affected zone(HAZ) of the Al-Mg-Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint.When the Al-Zn-Mg alloy was located at the advancing side(AS),the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.展开更多
To improve tensile-shear properties of fiction stir lap welded(FSLW) dissimilar Al/Mg joints, pin-tip profiles were innovatively designed and welding speed was optimized, and effects of them on formation, interface mi...To improve tensile-shear properties of fiction stir lap welded(FSLW) dissimilar Al/Mg joints, pin-tip profiles were innovatively designed and welding speed was optimized, and effects of them on formation, interface microstructure and mechanical properties of different FSLW joints were investigated. With increasing the welding speed, the tensile-shear load of FSLW joints produced by three pins presents an increasing firstly and then decreasing trend. Compared with Rpin, the hook and hole defect in the joints made by S-pin and T-pin are eliminated owing to additional eccentric force. Moreover, the joints obtained by T-pin at 75 mm/min have the highest tensile-shear load, and a maximum value of 3.425 kN is produced, which increases by 96.8%.Meanwhile, the pin-tip profile improves significantly the interface reaction depending on the welding temperature. For R-pin, thick brittle intermetallic compounds of about 6.9 μm Al3Mg2and 13.3 μm Al12Mg17layers at the welding interface derived from diffusion reaction are formed, resulting in continuous cracks. However, using T-pin can raise the interface temperature, and which makes the interface liquefy locally to generate only 2.2 μm Al3Mg2layer and dispersive(Al12-Mg17+Mg) eutectic structure. This can release high residual stress and remove welding crack, consequently enhancing the interface properties of T-pin joints.展开更多
The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding(EBW)technique.The anomalous microstructure containing the element transition zone(ETZ)and/or core of tail...The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding(EBW)technique.The anomalous microstructure containing the element transition zone(ETZ)and/or core of tail-like zone(CTLZ)is in the weld metal(WM)adjacent to the fusion line.The melting temperature difference between the WM and AISI 410 steel,melt stirring effect and element diffusion can trigger the formation of such anomalous microstructure.In particular,the larger distance of the region in WM away from the fusion line,the smaller CTLZ and larger ETZ occurred.Compared with the fine and ellipsoidal precipitates in the as-welded CTLZ,a large number of chain-type clustered precipitates were detected in the CTLZ and ETZ interface after the aging treatment at 566°C for 1000 h.The element diffusion under elevated temperature in WM is regarded as the crucial factor for such anomalous microstructure evolution during the aging treatment.展开更多
Ultrasonic-stationary shoulder assisted friction stir welding(U-SSFSW)is a novel hybrid welding technique,which reveals promising prospect in joining Al/Mg dissimilar alloys.A thorough understanding of U-SSFSW process...Ultrasonic-stationary shoulder assisted friction stir welding(U-SSFSW)is a novel hybrid welding technique,which reveals promising prospect in joining Al/Mg dissimilar alloys.A thorough understanding of U-SSFSW process is imperative for the further application of this technique.Pigeon-inspired optimization(PIO)is a swarm intelligent optimization algorithm and is proposed in mathematical modeling and process optimization by artificial intelligence.In this study,PIO optimized artificial neural network(PIOANN)was firstly established to acquire the relationships between the inputs and output of the Al/Mg welding process by U-SSFSW technique.A reliable PIO-ANN was achieved and the joint with a tensile strength of 161 MPa was acquired under the PIO optimized parameters.This tensile strength is higher than any ever-reported results with the similar welding condition.The joint formation,microstructure,microhardness and fracture behaviors were systemically investigated based on the reported studies and the confirmation experiment of this study to explore the enhancing mechanism of U-SSFSW Al/Mg joint.展开更多
Plasma-MIG hybrid arc welding is a hybrid heating source welding method which is composed of plasma arc and MIG arc. During Plasma-MIG hybrid arc welding process, the interface behavior of copper and steel dissimilar ...Plasma-MIG hybrid arc welding is a hybrid heating source welding method which is composed of plasma arc and MIG arc. During Plasma-MIG hybrid arc welding process, the interface behavior of copper and steel dissimilar alloy is investigated. The results show that electromagnetic stirring effect decreases and the heat input increases with the increase of outer plasma current in the hybrid arc welding process. The interface diffusion and interface thickness is controlled by the tradeoff of electromagnetic stirring effect degradation and heat input increase. The interface diffusion and interface thickness are controlled by decreasing the electromagnetic stirring force and increasing the heat input with the increase of plasma current in Cu/Fe plasma-MIG hybrid arc welding process.展开更多
基金National Natural Science Foundation of China(grant number 52075377 and 51575381)Tianjin Research Program of Application Foundation and Advanced Technology(grant number 15JCZDJC38600)supported by the China Scholarship Council(No.201706255090 and No.201806250043)。
文摘Components of Ti and Al dissimilar alloys were obtained by wire and arc additive manufacturing using two cold metal transfer(CMT)modes.Direct current CMT(DC-CMT)mode was used for Ti alloy deposition,and DC-CMT or CMT plus pulse(CMT+P)mode was used for the Al alloy deposition.During deposition of the first Al alloy layer,little and a significant amount of Ti alloy were melted using DC-CMT and CMT+P mode,respectively.TiAl_(3)formed in the reaction layer when DC-CMT mode was used,while TiAl_(3),TiAl,and Ti3Al formed in the reaction layer when CMT+P mode was used.Compared to using DC-CMT mode,more cracks occurred when using CMT+P.The nanohardness of the reaction layer was between that of the Al and Ti alloys,irrespective of the CMT modes.The average tensile strengths of the samples using DC-CMT and CMT+P mode were 108 MPa and 24 MPa,respectively.DC-CMT mode was more suitable for the wire and arc additive manufacturing of Ti/Al dissimilar alloys.
基金Funded in Part by the Grant from Technology and Industry for National Defense,China(No.AXXD1818)。
文摘Based on the investigated microstructure of different zones in the annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys,the mechanical property of them was assessed under fatigue crack growth rate tests.For evaluation of fatigue crack growth rate,three points bending specimens were used.The correlation between the range of stress intensity factor and crack growth rate was determined in different zones of the annealed weld joint.Fatigue crack growth rates were obviously different in different zones of weld joint of dissimilar titanium alloys,due to their different microstructures.Scanning electron microscope examinations were conducted on the fracture surface in order to determine the relevant fracture mechanisms and crack growth mechanisms with respect to the details of microstructure.
基金Supported by the National Natural Science Foundation of China(51801057,51702091,12104140)the Natural Science Foundation of Hubei Province(2020CFB245)+2 种基金the Hubei Province Education Department Scientific Research Plan Guiding Project(B2017215,B2021260)the Research Start-up Funding of Hubei University of Education(19RC03,20RC09)the 2021 Science and Technology Development Plan of Henan Province(212102210336)。
文摘In this research project,copper and stainless steel were connected by two laser welding methods:straight seam welding and swing welding.Then,electronic tensile test machine,X-ray diffractometer,scanning electron microscope and metallographic microscope were used to analyze the tensile properties,macroscopic and microscopic structure morphology and phase of the welded joint.Based on the experimental results,we determined that the strength of the straight seam welded joint was higher.Because of the intermetallic compound near the weld in the swing welding process,it leads to stress concentration,crack cracking and strength reduction.In addition,the oscillating laser beam also leads to the disorderly direction of columnar crystal and coarse structure,which makes the joint strength decrease.
基金the support provided by the China Scholarship Council(No.201806290070)the fund by the State Key Laboratory of Solidifi cation Processing in NWPU(No.2019-QZ-01)。
文摘This study focuses on the bonding interface characteristics and mechanical properties of the bobbin tool friction stir welded dissimilar AA6056 and AA2219 aluminum alloy joints using diff erent welding speeds.Voids arise solely in the stir zone at the AA2219 side.A distinct boundary with limited material mixing develops at the middle section of the bonding interface,while excellent material mixing with an irregularly jagged pattern forms at the top and bottom sections of the bonding interface.Increasing the welding speed,the material mixing is rarely changed at the middle section in comparison with the bottom section.Furthermore,a small diff erence between Guinier–Preston dissolution and Q phase precipitation leads to rare change of hardness in the heat aff ected zone(HAZ)at the AA6056 side.The increased hardness of the HAZ at the AA2219 side is attributed to avoidance of the dissolution ofθ’’phase precipitates.A maximum tensile strength of 181 MPa is obtained at 300 mm min-1.Fractures occur at the AA6056 side near the top and bottom surfaces and at the bonding interface in the middle section of the joints.The regions close to the top and bottom surfaces of the joints show a better ductility.
基金financially supported by the National Natural Science Foundation of China(No.51574196)the Natural Sciences and Engineering Research Council of Canada(NSERC)in the form of an international research collaboration+3 种基金the financial support by Premier’s Research Excellence Award(PREA)NSERC-Discovery Accelerator Supplement(DAS)AwardCanada Foundation for Innovation(CFI)Ryerson Research Chair(RRC)program。
文摘Cyclic deformation behavior of friction-stir-welded dissimilar AA2024-T351 to AA7075-T65 aluminum alloy joints was evaluated via stepwise tests at different strain rates,along with transmission electron microscopy examinations to characterize the precipitates required to assess internal stresses.Electron backscatter diffraction was employed to observe the inhomogeneous microstructures of the FSWed joints.Strain localization appeared in the heat affected zone(HAZ)of AA2024 side.After cyclic deformation of 500 cycles at a total strain amplitude of 0.5%,the strength of the dissimilar joints resumed basically to that of AA2024 base material.And the AA2024 HAZ was obviously hardened,which should be attributed to the introduced dislocations during cyclic deformation process.Cyclic hardening capacity of the joints increased with decreasing strain rate.
基金financially supported by the National Natural Science Foundation of China(No.51374048)the Fundamental Research Funds for the Central Universities(No.DUT16RC(3)009)
文摘The microstructure and mechanical properties of pulse metal inert-gas (MIG) welded dissimilar joints between 4 mm thick wrought 6061-T6 and cast A356-T6 aluminum alloy plates were investigated. The tensile strength of the joints reached 235 MPa, which is 83% of that of 6061 aluminum alloy, and then decreased with the increase of travel speed while keeping other welding parameters constant. The microstructure, composition and fractography of joints were examined by the optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Grain boundary liquation and segregation occurred in the partially melted zone (PMZ) on 6061 aluminum alloy side, and brittle Fe-rich phases were observed in partially melted zone on A356 aluminum alloy side. The minimum microhardness appeared in heat-affected zone (HAZ) near A356 aluminum alloy substrate. The samples during tensile test failed mainly in PMZ and HAZ on A356 aluminum alloy side through mixed fracture mode with quasi cleavage and dimples on fracture surface.
基金supported by the International S&T Cooperation Program of China(ISTCP) under grant No.2012DFR50580
文摘Friction stir welding(FSW) was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β' phases can be observed at the heat affected zone(HAZ) of the Al-Mg-Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint.When the Al-Zn-Mg alloy was located at the advancing side(AS),the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.52005240 and 52164045)Young Talent Program of Major Disciplines of Academic and Technical Leaders in Jiangxi Province(No.20212BCJ23028)Key Laboratory Fund Project(No.EG202180417).
文摘To improve tensile-shear properties of fiction stir lap welded(FSLW) dissimilar Al/Mg joints, pin-tip profiles were innovatively designed and welding speed was optimized, and effects of them on formation, interface microstructure and mechanical properties of different FSLW joints were investigated. With increasing the welding speed, the tensile-shear load of FSLW joints produced by three pins presents an increasing firstly and then decreasing trend. Compared with Rpin, the hook and hole defect in the joints made by S-pin and T-pin are eliminated owing to additional eccentric force. Moreover, the joints obtained by T-pin at 75 mm/min have the highest tensile-shear load, and a maximum value of 3.425 kN is produced, which increases by 96.8%.Meanwhile, the pin-tip profile improves significantly the interface reaction depending on the welding temperature. For R-pin, thick brittle intermetallic compounds of about 6.9 μm Al3Mg2and 13.3 μm Al12Mg17layers at the welding interface derived from diffusion reaction are formed, resulting in continuous cracks. However, using T-pin can raise the interface temperature, and which makes the interface liquefy locally to generate only 2.2 μm Al3Mg2layer and dispersive(Al12-Mg17+Mg) eutectic structure. This can release high residual stress and remove welding crack, consequently enhancing the interface properties of T-pin joints.
基金The authors gratefully acknowledge the National Natural Science Foundation of China(Grant Nos.U1760102 and 52101042).
文摘The Co-based alloy/AISI 410 stainless steel dissimilar welded joint was fabricated by the electron beam welding(EBW)technique.The anomalous microstructure containing the element transition zone(ETZ)and/or core of tail-like zone(CTLZ)is in the weld metal(WM)adjacent to the fusion line.The melting temperature difference between the WM and AISI 410 steel,melt stirring effect and element diffusion can trigger the formation of such anomalous microstructure.In particular,the larger distance of the region in WM away from the fusion line,the smaller CTLZ and larger ETZ occurred.Compared with the fine and ellipsoidal precipitates in the as-welded CTLZ,a large number of chain-type clustered precipitates were detected in the CTLZ and ETZ interface after the aging treatment at 566°C for 1000 h.The element diffusion under elevated temperature in WM is regarded as the crucial factor for such anomalous microstructure evolution during the aging treatment.
基金supported by the National Natural Science Foundation of China(No.51874201)the Science Technology Major Project of Liaoning Province,China(No.2019JH1/10100028)。
文摘Ultrasonic-stationary shoulder assisted friction stir welding(U-SSFSW)is a novel hybrid welding technique,which reveals promising prospect in joining Al/Mg dissimilar alloys.A thorough understanding of U-SSFSW process is imperative for the further application of this technique.Pigeon-inspired optimization(PIO)is a swarm intelligent optimization algorithm and is proposed in mathematical modeling and process optimization by artificial intelligence.In this study,PIO optimized artificial neural network(PIOANN)was firstly established to acquire the relationships between the inputs and output of the Al/Mg welding process by U-SSFSW technique.A reliable PIO-ANN was achieved and the joint with a tensile strength of 161 MPa was acquired under the PIO optimized parameters.This tensile strength is higher than any ever-reported results with the similar welding condition.The joint formation,microstructure,microhardness and fracture behaviors were systemically investigated based on the reported studies and the confirmation experiment of this study to explore the enhancing mechanism of U-SSFSW Al/Mg joint.
基金financially supported by the National Natural Science Foundation of China (Nos. 50974046 and 50904020)Twelfth Five-year Aerospace Project of China
文摘Plasma-MIG hybrid arc welding is a hybrid heating source welding method which is composed of plasma arc and MIG arc. During Plasma-MIG hybrid arc welding process, the interface behavior of copper and steel dissimilar alloy is investigated. The results show that electromagnetic stirring effect decreases and the heat input increases with the increase of outer plasma current in the hybrid arc welding process. The interface diffusion and interface thickness is controlled by the tradeoff of electromagnetic stirring effect degradation and heat input increase. The interface diffusion and interface thickness are controlled by decreasing the electromagnetic stirring force and increasing the heat input with the increase of plasma current in Cu/Fe plasma-MIG hybrid arc welding process.