ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding...ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters.The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone(SZ)followed by evolution of a bimodal grain structure with distributed bands of 0.8-1.7μm ultrafine grains and 4.1-7.1μm equiaxed grains.Micro-hardness of SZ is substantially reduced in contrast to that of parent metal(PM)in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix.With the decrease in traverse speed,randomization degree of the plasticized metal flow increases,which is evidenced by the randomized arc line pattern at the low traverse speed.Among all defect-free joints,the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties,which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%,respectively,as compared to the PM.The randomized texture hinders the joint fracturing within SZ at low elongation.Therefore,a relatively high elongation of 10.8% was achieved,which corresponded to 72% of the PM value.展开更多
7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding （SS-FSW and BB-FSW, respectively） at different welding parameters. The temperature distributi...7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding （SS-FSW and BB-FSW, respectively） at different welding parameters. The temperature distribution, microstructure evolution and mechanical properties of joints along the thickness direction were investigated, and digital image correlation （DIC） was utilized to evaluate quantitatively the deformation of different zones during tensile tests. The results indicated that heat-affected zone （HAZ）, the local softening region, was responsible for the early plastic deformation and also the fracture location for SS-FSW samples, while a rapid fracture was observed in weld nugget zone （WNZ） before yield behavior for all BB-FSW specimens. The ultimate tensile strength （UTS） of SS-FSW joints presented the highest value of 410 MPa, 82% of the base material, at a rotational speed of 300 rpm and welding speed of 60 mm/min, much higher than that of BB-FSW joints, with a joint efficiency of only 47%. This should be attributed to the Lazy S defect produced by a larger extent of heat input during the BB-FSW process, The whole joint exhibited a much higher elongation than the slices. Scanning electron microscopic （SEM） analysis of the fracture morphologies showed that joints failed through ductile fracture for SS-FSW and brittle fracture for BB-FSW.展开更多
A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm t...A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm thick alunlinum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formabiliW. Experimental results show that compared to conven- tional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.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
In the present study,2219-T87 Al alloy plates,4 mm in thickness,were subjected to bobbin tool friction stir welding(BTFSW)under relatively high welding speeds of 200 and 400 mm/min,with the aim to analyze the effect o...In the present study,2219-T87 Al alloy plates,4 mm in thickness,were subjected to bobbin tool friction stir welding(BTFSW)under relatively high welding speeds of 200 and 400 mm/min,with the aim to analyze the effect of welding speeds on fatigue properties of the joints.The results showed that the tension–tension high-cycle fatigue performance of the BT-FSW joints at room temperature was significantly enhanced compared to that of other joints of 2xxx series Al alloys counterparts.Particularly at a high welding speed of 400 mm/min,the fatigue strength of the joint reached 78%of the base material together with a high tensile strength of 311 MPa.It was found that the joint line remnants had no effects on the fatigue properties of the BT-FSW joints due to the elimination of root flaws under the action of the lower shoulder.Most of the samples with the welding speed of 200 mm/min failed at the thermo-mechanical zone(TMAZ)during fatigue tests,attributable to the coarsened grains and precipitates,but all of the samples with high welding speed of 400 mm/min randomly failed at the nugget zone due to the improved hardness value in the TMAZ.展开更多
Research work presented in this study has the primary target of exploring joint attributes of AZ31 magnesium alloys using friction stir welding process with a modified tool referred as bobbin tool.Effects of inert and...Research work presented in this study has the primary target of exploring joint attributes of AZ31 magnesium alloys using friction stir welding process with a modified tool referred as bobbin tool.Effects of inert and open atmosphere on mechanical properties are evaluated over a wide range of welding speed and tool rotation speed.Comparison of the research findings from the inert atmosphere bobbin tool were made with the traditional process of friction stir welding.The results depicted improved joint properties for inert atmosphere welding.Low and intermediate range of tool rotational speed is found to be favorable for bobbin tool friction stir welding without and with an inert medium,respectively.Controlled atmosphere due to inert medium leads to less oxidation of the AZ31 Mg alloy leading to superior joint properties.Microstructural investigations are also made with the aim of evaluating the impact of bobbin tool and inert medium on joint properties.In each aspect for joining of AZ31 Mg alloy,bobbin tool with inert medium is found to be an effective solution for joining with improved mechanical properties compared to without inert bobbin tool as well as conventional tool friction stir welding.展开更多
Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid b...Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid backing anvil,which expands the potential application of FSW in aerospace,railway,automotive and marine industries.BT-FSW has some signifi cant advantages over conventional FSW such as no root fl aws,full weld penetration,low stiff ness requirements for machines and fi xtures,balanced heat input,lower distortion and thus has broad prospects for development.At present,there have been numerous research reports on BT-FSW,but its widespread use is still restricted due to various factors such as tool life,process stability,control complexity and implementation cost.In this paper,the domestic and foreign research progress of BT-FSW is reviewed from four aspects of bobbin tool design and classifi cation,temperature fi eld and fl ow fi eld during welding,microstructure and mechanical properties of welded joints as well as industrial application,and then the possible research hotspots of BT-FSW in the future are pointed out.This paper mainly aims to help researchers have a comprehensive and in-depth understanding of BT-FSW.展开更多
Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, mi...Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, microhardness, and tensile properties of the aged and as-welded specimens were investigated. Transmission electron microscopy (TEM) observations revealed that a large number of Guinier–Preston (GP) zones precipitated in the form of a network on the stir zone (SZ) after PWNA for 60 d, and a large number of β'' phases precipitated in the matrix for after PWAA for 6 h. As the aging time increased, the microhardness of the SZ and the thermomechanically affected zone (TMAZ) increased significantly, and the hardness of the SZ after PWAA for 6 h was close to that of the base metal (BM). With increasing PWNA time, the strength and strain increased slightly. When the PWAA time increased, the strength clearly increased, with a maximum value of 279.9 MPa after 6 h, while the strain decreased.展开更多
基金sponsored by the National Science and Technology Major Project(No.2017ZX04005001)the Key Research and Development program of Shandong(No.2018GGX103053)。
文摘ZK60B(Mg-6%Zn-0.6%Zr)alloy joints fabricated by bobbin tool friction stir welding(BTFSW)with various traverse speeds were investigated.The sound joint fabricated by the BTFSW was possible under the appropriate welding parameters.The severe plastic deformation during BTFSW resulted in dispersion and segregation of the Zr-rich particles within the stirred zone(SZ)followed by evolution of a bimodal grain structure with distributed bands of 0.8-1.7μm ultrafine grains and 4.1-7.1μm equiaxed grains.Micro-hardness of SZ is substantially reduced in contrast to that of parent metal(PM)in spite of the finer grain size owing to dissolution of Mg-Zn based precipitates having hardening effects on alpha-Mg matrix.With the decrease in traverse speed,randomization degree of the plasticized metal flow increases,which is evidenced by the randomized arc line pattern at the low traverse speed.Among all defect-free joints,the 200 mm/min joint exhibits the weakest isotropy of texture within SZ and the best tensile properties,which has reduced ultimate tensile strength and yield strength by 5.4% and by 22.2%,respectively,as compared to the PM.The randomized texture hinders the joint fracturing within SZ at low elongation.Therefore,a relatively high elongation of 10.8% was achieved,which corresponded to 72% of the PM value.
基金financial support of the project from the National Natural Science Foundation of China(No.51405392)Specialized Research Fund for the Doctoral Program of Higher Education(No.20136102120022)Hong Kong Scholar Program(No.XJ2016043)
文摘7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding （SS-FSW and BB-FSW, respectively） at different welding parameters. The temperature distribution, microstructure evolution and mechanical properties of joints along the thickness direction were investigated, and digital image correlation （DIC） was utilized to evaluate quantitatively the deformation of different zones during tensile tests. The results indicated that heat-affected zone （HAZ）, the local softening region, was responsible for the early plastic deformation and also the fracture location for SS-FSW samples, while a rapid fracture was observed in weld nugget zone （WNZ） before yield behavior for all BB-FSW specimens. The ultimate tensile strength （UTS） of SS-FSW joints presented the highest value of 410 MPa, 82% of the base material, at a rotational speed of 300 rpm and welding speed of 60 mm/min, much higher than that of BB-FSW joints, with a joint efficiency of only 47%. This should be attributed to the Lazy S defect produced by a larger extent of heat input during the BB-FSW process, The whole joint exhibited a much higher elongation than the slices. Scanning electron microscopic （SEM） analysis of the fracture morphologies showed that joints failed through ductile fracture for SS-FSW and brittle fracture for BB-FSW.
基金support of the National Natural Science Foundation of China(No.51705027)the fund of the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP201722)
文摘A novel dual-rotation bobbin tool friction stir welding （DBT-FSW） was developed, in which the upper shoulder （US） and lower shoulder （LS） have different rotational speeds. This process was tried to weld 3.2 mm thick alunlinum-lithium alloy sheets. The metallographic analysis and torque measurement were carried out to characterize the weld formabiliW. Experimental results show that compared to conven- tional bobbin tool friction stir welding, the DBT-FSW has an excellent process stability, and can produce the defect-free joints in a wider range of welding parameters. These can be attributed to the significant improvement of material flow caused by the formation of a staggered layer structure and the unbalanced force between the US and LS during the DBT-FSW process.
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 LiaoNing Revitalization Talents Program under grant No.XLYC2002099the LiaoNing Province Excellent Youth Foundation(No.2021-YQ-01)+1 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.Y2021061)the IMR Innovation Fund(No.2022-PY11).
文摘In the present study,2219-T87 Al alloy plates,4 mm in thickness,were subjected to bobbin tool friction stir welding(BTFSW)under relatively high welding speeds of 200 and 400 mm/min,with the aim to analyze the effect of welding speeds on fatigue properties of the joints.The results showed that the tension–tension high-cycle fatigue performance of the BT-FSW joints at room temperature was significantly enhanced compared to that of other joints of 2xxx series Al alloys counterparts.Particularly at a high welding speed of 400 mm/min,the fatigue strength of the joint reached 78%of the base material together with a high tensile strength of 311 MPa.It was found that the joint line remnants had no effects on the fatigue properties of the BT-FSW joints due to the elimination of root flaws under the action of the lower shoulder.Most of the samples with the welding speed of 200 mm/min failed at the thermo-mechanical zone(TMAZ)during fatigue tests,attributable to the coarsened grains and precipitates,but all of the samples with high welding speed of 400 mm/min randomly failed at the nugget zone due to the improved hardness value in the TMAZ.
基金The present work was supported from Mechanical Engineering Department and Central Instruments Facility,Indian Institute of Technology Guwahati for experiment and conduct testing.
文摘Research work presented in this study has the primary target of exploring joint attributes of AZ31 magnesium alloys using friction stir welding process with a modified tool referred as bobbin tool.Effects of inert and open atmosphere on mechanical properties are evaluated over a wide range of welding speed and tool rotation speed.Comparison of the research findings from the inert atmosphere bobbin tool were made with the traditional process of friction stir welding.The results depicted improved joint properties for inert atmosphere welding.Low and intermediate range of tool rotational speed is found to be favorable for bobbin tool friction stir welding without and with an inert medium,respectively.Controlled atmosphere due to inert medium leads to less oxidation of the AZ31 Mg alloy leading to superior joint properties.Microstructural investigations are also made with the aim of evaluating the impact of bobbin tool and inert medium on joint properties.In each aspect for joining of AZ31 Mg alloy,bobbin tool with inert medium is found to be an effective solution for joining with improved mechanical properties compared to without inert bobbin tool as well as conventional tool friction stir welding.
文摘Bobbin tool friction stir welding(BT-FSW)is a variant of conventional friction stir welding(FSW).It can be used to weld complex curvature structures and closed sections by adding an extra shoulder instead of a rigid backing anvil,which expands the potential application of FSW in aerospace,railway,automotive and marine industries.BT-FSW has some signifi cant advantages over conventional FSW such as no root fl aws,full weld penetration,low stiff ness requirements for machines and fi xtures,balanced heat input,lower distortion and thus has broad prospects for development.At present,there have been numerous research reports on BT-FSW,but its widespread use is still restricted due to various factors such as tool life,process stability,control complexity and implementation cost.In this paper,the domestic and foreign research progress of BT-FSW is reviewed from four aspects of bobbin tool design and classifi cation,temperature fi eld and fl ow fi eld during welding,microstructure and mechanical properties of welded joints as well as industrial application,and then the possible research hotspots of BT-FSW in the future are pointed out.This paper mainly aims to help researchers have a comprehensive and in-depth understanding of BT-FSW.
文摘Samples of 6082-T6 aluminum alloy were subjected to bobbin tool friction stir welding (BT-FSW), and the joints were treated by postweld natural aging (PWNA) and postweld artificial aging (PWAA). The microstructure, microhardness, and tensile properties of the aged and as-welded specimens were investigated. Transmission electron microscopy (TEM) observations revealed that a large number of Guinier–Preston (GP) zones precipitated in the form of a network on the stir zone (SZ) after PWNA for 60 d, and a large number of β'' phases precipitated in the matrix for after PWAA for 6 h. As the aging time increased, the microhardness of the SZ and the thermomechanically affected zone (TMAZ) increased significantly, and the hardness of the SZ after PWAA for 6 h was close to that of the base metal (BM). With increasing PWNA time, the strength and strain increased slightly. When the PWAA time increased, the strength clearly increased, with a maximum value of 279.9 MPa after 6 h, while the strain decreased.
