Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint ...Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.展开更多
Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configuration...Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configurations, namely inclined butt(conventional butt) and serrated interlocking(innovative butt), are proposed for improving weld formation and joint quality. The results show that a continuous and straight intermetallic compound layer appears at the Mg side interface in conventional butt joint, and the maximum average thickness reaches about 60.1 μm.Additionally, the Mg side interface also partially melts, forming a eutectic structure composed of Mg solid solution and Al_(12)Mg_(17) phase.For the innovative butt joint, the Mg side interface presents the curved interlocking feature, and intermetallic compounds can be reduced to less than 10 μm. The joint strength of innovative butt joint is more than three times that of conventional butt joint. This is due to the interlocking effect and thin intermetallic compounds in the innovative joint.展开更多
The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir we...The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir welding(FSW),and the microstructure and mechanical property of the joint were systemically characterized.The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint.The joint was divided into stir zone of Al(ST-Al),stir zone of interface(ST-I),thermal-mechanically affected zone of steel(TMAZ-Fe)and base material of steel(BM-Fe)according to their distinct microstructure vertically.Three kinds of intermetallic compounds(IMCs)of FeAl_(3),FeAl and Fe_(3)Al were formed at the interface.The horizontal micro hardness distribution exhibited a hat shape and“M”shape in Al and steel,respectively.The hardest region of the joint was located at the ST-I,with a hardness of 175 HV−210 HV.The joint was fractured along the hook structure,with an average shear strength of 73.9 MPa.Fractural morphology of Al and steel indicted a cleavage fracture mode.展开更多
To quantify the nonuniform micromechanical performance of welded joint,the load-displacement curves by nanoindentation test were introduced to examine different zones including base metal,coarse grained heat affected ...To quantify the nonuniform micromechanical performance of welded joint,the load-displacement curves by nanoindentation test were introduced to examine different zones including base metal,coarse grained heat affected zone,partially melted zone,weld metal near the fusion boundary and weld metal center.The results showed that the strengthening effect of weld metal was more obvious than that of heat affected zone for nickel based welded joint and especially in coarse grained heat affected zone,the hardening resulted from overheating was not apparent.Nickel based weld metal with high content of alloying elements which were often segregated at interdendritic regions or precipitated in grain interior under nonequilibrium solidification contributed to the characteristics that differ from conventional low alloy steel welded joint.展开更多
Flame heating combined with water cooling was used to straighten A6N01 aluminum alloy welded joint and effect of flame heating pass on its microstructure and mechanical properties was studied. Results showed that the ...Flame heating combined with water cooling was used to straighten A6N01 aluminum alloy welded joint and effect of flame heating pass on its microstructure and mechanical properties was studied. Results showed that the flame induced the precipitation and growth of the Mg_2Si phase on the Al substrate for the thermal aging A6N01 aluminum alloy welded joints,thus it led the decrease of micro-hardness and tensile strength of the A6N01 aluminum alloy welded joint with the increase of the heating pass. However,the fatigue property of the flame heated joint was improved because the Mg_2Si precipitation hindered the initiation and propagation of the fatigue crack.展开更多
The current research of low cycle fatigue(LCF) is mainly focused on the components with uniform microstructure.Compared with these typical components, LCF behavior of welded components are more complex due to their gr...The current research of low cycle fatigue(LCF) is mainly focused on the components with uniform microstructure.Compared with these typical components, LCF behavior of welded components are more complex due to their great gradient microstructure, especially for di erent temperature. In this paper, LCF properties were conducted on the welded joint at di erent temperatures for bainite steel, and the failure mechanism was systematically discussed.Fatigue parameters derived from fitting curves indicated that welded joint had worse plastic deformation resistance and experienced more significantly strain hardening e ect at 300 °C. The joint failed in the weld metal at room temperature, which attributed to the softening in weld metal combined with cyclic strain hardening e ect in heata ected zone, which meant the joint was more sensitive with the hardness at this condition. When it came to 300 °C,more cracks appeared near to HAZ and the heterogeneous distributed surface inclusion was responsible for the fracture transition to HAZ adjacent to bainite steel rather than the softest zone in HAZ, reflecting the joint was more sensitive with the surface inclusion at 300 °C. This research could support the design on loading of welded component at di erent temperature, and further ensure the safe operation.展开更多
In this paper, to meet the needs of studying work of dynamic mechanical properties of welded joint, the dynamic mechanical properties of welded joint were measured by means of SHPB(Split Hopkinson Pressure Bar).The dy...In this paper, to meet the needs of studying work of dynamic mechanical properties of welded joint, the dynamic mechanical properties of welded joint were measured by means of SHPB(Split Hopkinson Pressure Bar).The dynamic mechanical property’s curves of every part of welded joint were obtained. For studying the dynamic behavior of mechanical heterogeneity of welded joint, important data were offered. The method of test creates a new way of studying dynamic mechanical properties of welded joint.展开更多
The effect of Zn interlayer on the microstructural evolution and mechanical behavior of dissimilar ultrasonic-spot-welded Al/Cu joints was investigated.The tensile lap shear strength in relation to welding energy was ...The effect of Zn interlayer on the microstructural evolution and mechanical behavior of dissimilar ultrasonic-spot-welded Al/Cu joints was investigated.The tensile lap shear strength in relation to welding energy was analyzed.The experimental results show that two intermetallic compounds,Cu5Zn8 and Al2Cu,were generated at the interface of the ultrasonic-spotwelded Al/Cu joint with a Zn interlayer.The primary joining mechanisms of the joint included the intermetallic compound bonding and metallic bonding caused by solid shear plastic deformation.Meanwhile,with increasing welding energy,the plastic deformation of the material became more substantial.With increasing welding energy,the tensile lap shear strength of the joints first increased and then decreased for the ultrasonic-spot-welded Al/Cu joints with and without Zn interlayers.Under the energy input of 700 J,the bearing load capacity of the ultrasonic-spot-welded Al/Cu joints with a Zn interlayer improved signifi cantly due to the observed intermetallic compound(Cu5Zn8).展开更多
Relationships between microstructures of welded joint and welding parameters or weld strength of aluminium matrix composite Al2O3p/6061 subjected to diffusion welding were studied. The results are as follows: key fact...Relationships between microstructures of welded joint and welding parameters or weld strength of aluminium matrix composite Al2O3p/6061 subjected to diffusion welding were studied. The results are as follows: key factor affecting strength of welded joint is oxide in the weld zone. The existence of oxide in the welded joint not only hinders the diffusion of the matrix atoms, but also destroys the good interface between the matrix and the reinforced phase. The oxides turn into fine particles from film with increasing welding temperature, and the destroying effect on welded joint decreases, which increases the strength of the welded joint. On the basis of this, the diffusion welding of aluminium matrix composite Al2O3p/6061 was successfully realized.展开更多
Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a ...Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a nd mechanical properties. Electron Beam Welding (EBW) process has been found to be especially well suited in this area. Selection of the appropriate welding par ameters needs thorough investigations. These parameters include: preheat tempera ture (℃), welding current (I w), focusing current (I F), welding spee d (V), height between the gun and workpiece surface (H), scan width (S w) and shift distance (S). The present work aims firstly, setting the pr oper welding conditions to get sound joint between commercially pure copper (C10 200) and AISI 316 stainless steel plates 8 mm thickness. Secondly, investigate t he effect of Electron Beam (EB) shift, single-sided and double-sided welds on the mechanical, metallurgical and chemical properties of the weld bead. Due to t he high difference in thermal conductivity between copper and stainless steel, E lectron Beam (EB) was shifted towards copper with different values. These values were ranged from 0.3 to 0.9 mm in welding without preheating of copper plate an d from 0.1 to 0.4 mm with preheating. Number of joints were welded using variabl e EBW parameters in view to obtain the sound weld bead. These parameters are as follows: gradual reduction I w=51 to 49 mA, I F=845 mA, V=8 mm/sec , H=130 mm, S w=500 μm and S=0.4 mm. The investigation has shown t hat, the copper (C10200) plate must be preheated to get sound welded joint with AISI 316 stainless steel using the EBW process. The tensile fracture in all wel ded samples occurred in copper plate away from the weld bead. This reflects that the weld bead tensile strength is greater than the copper strength. The EB shif t has slight effect on hardness distribution through weld bead. The hardness val ue (H v) reduces in gradual manner from stainless steel hardness to copper one. The EB shift distance has no significant effect on the impact toughness.展开更多
Al-6Mg alloy with trace Sc addition was prepared by means of melting-casting.The samples of the welded joints of Al-6Mg alloy with trace Sc addition were made by method of manual argon-arc welding.Neutral salt spray t...Al-6Mg alloy with trace Sc addition was prepared by means of melting-casting.The samples of the welded joints of Al-6Mg alloy with trace Sc addition were made by method of manual argon-arc welding.Neutral salt spray test was carried out by referring to GB/T10125-1997 and GB6384-1986 practice.Exfoliation testing was carried out in accordance with the method of Al-Mg alloy exfoliation corrosion test.The corrosion behaviors of the welded joints of AlMg alloy with high level of Mg and trace Sc addition were studied.The microstructures of the welded joints were observed by using optical microscope and transmission electron microscope.The corrosion resistance mechanism of the alloy was also involved.This work intended to determine if the welded joints of Al-6Mgalloy with trace Sc addition can have excellent corrosion resistance, when their strength are clearly improved.The results show that trace content of Sc refines the grains of alloys effectively, raises remarkably the corrosion resistance of the welded joints of Al-6Mg alloy with trace Sc addition.The corrosion resistance mechanisms are that there is free of continuous grain boundary precipitation or network which could be susceptible to corrosion in the microstructure of welded joints.展开更多
In modern fossil and nuclear power plants,the components are subjected to creep,fatigue,and creep-fatigue(CF)due to frequent start-up and shut-down operations at high temperatures.The CF interaction on the in-service ...In modern fossil and nuclear power plants,the components are subjected to creep,fatigue,and creep-fatigue(CF)due to frequent start-up and shut-down operations at high temperatures.The CF interaction on the in-service P92 steel welded joint was investigated by strain-controlled CF tests with different dwell times of 30,120,300,600 and 900 s at 650℃.Based on the observations of the fracture surface by scanning electron microscope(SEM),the character-istic microstructure of fatigue-induced damage was found for the CF specimens with short dwell times(30 and 120 s).The hardness,elastic modulus and creep deformation near the fracture edges of four typical CF specimens with 30,120,600 and 900 s dwell times were measured by nanoindentation.Compared to specimens with post-weld heat treatment(PWHT),lower hardness and creep strength were found for all CF specimens.In addition,significant reduc-tions in hardness,elastic modulus,and creep strength were measured near the fracture edges for the CF specimens with short dwell times compared to the PWHT specimens.Compared to PWHT specimens(0.007),the increased strain rate sensitivities(SRS)of 0.010 to 0.17 were estimated from secondary creep.The increased values of SRS indicate that the room temperature creeps behavior is strongly affected by the decrease in dislocation density after the CF tests.展开更多
It is essential to understand the weld interface characteristics and mechanical properties of dissimilar joints to improve its quality.This study is aimed at exploring the properties of friction welded magnesium-titan...It is essential to understand the weld interface characteristics and mechanical properties of dissimilar joints to improve its quality.This study is aimed at exploring the properties of friction welded magnesium-titanium dissimilar joint using tensile testing coupled with digital image correlation,optical and scanning electron microscopy,x-ray diffraction and microhardness measurements.Microstructurally different regions such as contact zone,dynamic recrystallized zone,thermo-mechanically affected zone,and partially deformed zone in the magnesium side were observed.No discernible regions were observed in the titanium side,as it had not undergone any significant plastic deformation.Phase analysis indicated that the aluminium from the magnesium side diffused toward the weld interface and formed a thin continuous intermetallic layer by reacting with the titanium.Microhardness mapping showed a steep hardness gradient from the titanium to magnesium side.Critical analysis is done on the tensile characteristics of the specimen and the response of the local regions to the deformation process is mapped.展开更多
The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion(EXCO) solution. Electrochemical measurements(open circuit potential, poten...The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion(EXCO) solution. Electrochemical measurements(open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy), scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase(Al2Cu) after 2 h of immersion in EXCO solution.展开更多
The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical propertie...The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track,and the design method of CWR and track structures on the beam ends are proposed.The results show that the unidirectional Rail Expansion Joints(REJ)need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force.Due to the bridge characteristics,there is no CWR fixed area on the kilometer-span bridge,and rail longitudinal force on the main span caused by bending loads needs to be concerned.The deformation of track on the beam end is complex,which is the weak area on the kilometer bridge,the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end,small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end.To improve the driving safety and comfort of beam end,the Sleeper-Supporting Apparatus(SSA)should be specially designed to ensure the uniform transition of track on beam ends.Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge,the dynamic response of trains and bridges under those loads needs to be attended to.展开更多
With thick plates of 2219 high-strength alloy, the microstructures of welded joints with twin wire MIG welding were analyzed. Experimental results show that no hot crack was found in the weld due to discontinuous dist...With thick plates of 2219 high-strength alloy, the microstructures of welded joints with twin wire MIG welding were analyzed. Experimental results show that no hot crack was found in the weld due to discontinuous distribution of cocrystallization with low melting temperature, but porosity is serious in the first weld seam that is mainly composed of equiaxial grains with uneven sizes. As the poor position of the whole welded joint, fusion zone has big and coarse grains, uneven microstructures; In quenching zone, there exist a lot of soaked microstructures that cocrystallization with low melting temperature solute into matrix, thus strengthening the metal in this zone; In excessive aging zone, much more phases that distribute evenly will be separated from the matrix; Outside this zone, properties and microstructures of the metal are basically similar to matrix due to the relatively low temperature or unaffected heat in the zone during welding.展开更多
The microstructures, the changing rule of carbon-enriched zone, the diffusion behaviors of elements C and Cr, and the carbide type of 0Cr6Mn13Ni10MoTi/1Cr5Mo dissimilar welded joints after aging at 500℃ for various t...The microstructures, the changing rule of carbon-enriched zone, the diffusion behaviors of elements C and Cr, and the carbide type of 0Cr6Mn13Ni10MoTi/1Cr5Mo dissimilar welded joints after aging at 500℃ for various times and after long-term service in technical practice were investigated by using the optical microscopy, electron probe microanalysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that in aging 0Cr6Mn13Ni10MoTi/1Cr5Mo dissimilar welded joints, the main carbides are M3C and a few carbides are M7C3 and M23C6. The M3C carbide decomposition and dissolution with increasing aging time or aging temperature and the anti-diffusion of C and Cr cause the decrease and disappearance of the carbon-enriched zone. The results are different from those of the A302/1Cr5Mo dissimilar welded joints in previous studies.展开更多
The fatigue contrast tests of unload longitudinal direction corner joints as original welded and treated by ultrasonic peening of Q235B in various stress ratio are directed. The improvements of fatigue performance of ...The fatigue contrast tests of unload longitudinal direction corner joints as original welded and treated by ultrasonic peening of Q235B in various stress ratio are directed. The improvements of fatigue performance of unload longitudinal direction corner joints resulted by ultrasonic peening are studied. The effect pattern of stress ratio on fatigue performance of welded joints that are treated by ultrasonic peening is studied. As tests results indicate that: ① In the condition of stress ratio R= -1, the fatigue strength of specimen treated by ultrasonic peening is increased by 165% of that of the original welded specimen. And the fatigue life of specimen treated by ultrasonic peening is as much as 75～210 times of that of the latter. When R=0.1, the fatigue strength is increased by 87% and the fatigue life is extended by 21～29 times. When R= -0.5, the fatigue strength is increased by 123% and the fatigue life is extended by 42～59 times. When R=0.45, the fatigue strength is increased by 51% and the fatigue life is extended by 3～14 times. ② If the welded joints are treated by ultrasonic peening, the fatigue strength is no longer independent on the applied mean stress. The more the stress ratio R, the less the fatigue stress range which can be sustained by the joints is. ③ Whether the high value residual stress is in the joints or not, the dead load portion of the applied load must be considered in the design of the joints which should be treated by ultrasonic peening.展开更多
7A52 Al alloy plate aged at 105 ℃ for 8 h and then at 130 ℃ for 24 h was welded by means of TIG using Al- 6.3Mg-0.35Sc-0.1Zr-0.1Cr solder wire. Mechanical properties and microstructures of welded joint were studied....7A52 Al alloy plate aged at 105 ℃ for 8 h and then at 130 ℃ for 24 h was welded by means of TIG using Al- 6.3Mg-0.35Sc-0.1Zr-0.1Cr solder wire. Mechanical properties and microstructures of welded joint were studied. There are two obviously soft areas in the welded joint, welding seam and over-aging zone. The mechanical properties of welded joint are that σb is 358 MPa, σ0.2 is 238 MPa and δ5 is 6.6%. 75.6% of welding coefficient can be achieved. The addition of scandium leads to very significant grain refinement in the fusion zone, which results in a reduction in solidification cracking tendency. The solidification cracking isn’t observed.展开更多
文摘Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.
基金supported by the National Natural Science Foundation of China (No.51874179,52005240 and 52164045)the Young Talent Program of Major Disciplines of Academic and Technical Leaders in Jiangxi Province (No.20212BCJ23028)。
文摘Friction stir welding of dissimilar Al/Mg thick plates still faces severe challenges, such as poor formability, formation of thick intermetallic compounds, and low joint strength. In this work, two joint configurations, namely inclined butt(conventional butt) and serrated interlocking(innovative butt), are proposed for improving weld formation and joint quality. The results show that a continuous and straight intermetallic compound layer appears at the Mg side interface in conventional butt joint, and the maximum average thickness reaches about 60.1 μm.Additionally, the Mg side interface also partially melts, forming a eutectic structure composed of Mg solid solution and Al_(12)Mg_(17) phase.For the innovative butt joint, the Mg side interface presents the curved interlocking feature, and intermetallic compounds can be reduced to less than 10 μm. The joint strength of innovative butt joint is more than three times that of conventional butt joint. This is due to the interlocking effect and thin intermetallic compounds in the innovative joint.
文摘The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir welding(FSW),and the microstructure and mechanical property of the joint were systemically characterized.The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint.The joint was divided into stir zone of Al(ST-Al),stir zone of interface(ST-I),thermal-mechanically affected zone of steel(TMAZ-Fe)and base material of steel(BM-Fe)according to their distinct microstructure vertically.Three kinds of intermetallic compounds(IMCs)of FeAl_(3),FeAl and Fe_(3)Al were formed at the interface.The horizontal micro hardness distribution exhibited a hat shape and“M”shape in Al and steel,respectively.The hardest region of the joint was located at the ST-I,with a hardness of 175 HV−210 HV.The joint was fractured along the hook structure,with an average shear strength of 73.9 MPa.Fractural morphology of Al and steel indicted a cleavage fracture mode.
基金supported by the Primary Research&Developement Plan of Jiangsu Province(BE2017168)
文摘To quantify the nonuniform micromechanical performance of welded joint,the load-displacement curves by nanoindentation test were introduced to examine different zones including base metal,coarse grained heat affected zone,partially melted zone,weld metal near the fusion boundary and weld metal center.The results showed that the strengthening effect of weld metal was more obvious than that of heat affected zone for nickel based welded joint and especially in coarse grained heat affected zone,the hardening resulted from overheating was not apparent.Nickel based weld metal with high content of alloying elements which were often segregated at interdendritic regions or precipitated in grain interior under nonequilibrium solidification contributed to the characteristics that differ from conventional low alloy steel welded joint.
文摘Flame heating combined with water cooling was used to straighten A6N01 aluminum alloy welded joint and effect of flame heating pass on its microstructure and mechanical properties was studied. Results showed that the flame induced the precipitation and growth of the Mg_2Si phase on the Al substrate for the thermal aging A6N01 aluminum alloy welded joints,thus it led the decrease of micro-hardness and tensile strength of the A6N01 aluminum alloy welded joint with the increase of the heating pass. However,the fatigue property of the flame heated joint was improved because the Mg_2Si precipitation hindered the initiation and propagation of the fatigue crack.
基金Supported by National Natural Science Foundation of China(Grant Nos.51675336,U1660101,and 51775338)
文摘The current research of low cycle fatigue(LCF) is mainly focused on the components with uniform microstructure.Compared with these typical components, LCF behavior of welded components are more complex due to their great gradient microstructure, especially for di erent temperature. In this paper, LCF properties were conducted on the welded joint at di erent temperatures for bainite steel, and the failure mechanism was systematically discussed.Fatigue parameters derived from fitting curves indicated that welded joint had worse plastic deformation resistance and experienced more significantly strain hardening e ect at 300 °C. The joint failed in the weld metal at room temperature, which attributed to the softening in weld metal combined with cyclic strain hardening e ect in heata ected zone, which meant the joint was more sensitive with the hardness at this condition. When it came to 300 °C,more cracks appeared near to HAZ and the heterogeneous distributed surface inclusion was responsible for the fracture transition to HAZ adjacent to bainite steel rather than the softest zone in HAZ, reflecting the joint was more sensitive with the surface inclusion at 300 °C. This research could support the design on loading of welded component at di erent temperature, and further ensure the safe operation.
文摘In this paper, to meet the needs of studying work of dynamic mechanical properties of welded joint, the dynamic mechanical properties of welded joint were measured by means of SHPB(Split Hopkinson Pressure Bar).The dynamic mechanical property’s curves of every part of welded joint were obtained. For studying the dynamic behavior of mechanical heterogeneity of welded joint, important data were offered. The method of test creates a new way of studying dynamic mechanical properties of welded joint.
基金supported by the National Key R&D Program of China(2018YFB1107900)the National Natural Science Foundation of China and Civil Aviation Administration of China(U1933129)+1 种基金the Natural Science Foundation of Tianjin City(18JCQNJC04100)the National Natural Science Foundation of China(51575383).
文摘The effect of Zn interlayer on the microstructural evolution and mechanical behavior of dissimilar ultrasonic-spot-welded Al/Cu joints was investigated.The tensile lap shear strength in relation to welding energy was analyzed.The experimental results show that two intermetallic compounds,Cu5Zn8 and Al2Cu,were generated at the interface of the ultrasonic-spotwelded Al/Cu joint with a Zn interlayer.The primary joining mechanisms of the joint included the intermetallic compound bonding and metallic bonding caused by solid shear plastic deformation.Meanwhile,with increasing welding energy,the plastic deformation of the material became more substantial.With increasing welding energy,the tensile lap shear strength of the joints first increased and then decreased for the ultrasonic-spot-welded Al/Cu joints with and without Zn interlayers.Under the energy input of 700 J,the bearing load capacity of the ultrasonic-spot-welded Al/Cu joints with a Zn interlayer improved signifi cantly due to the observed intermetallic compound(Cu5Zn8).
文摘Relationships between microstructures of welded joint and welding parameters or weld strength of aluminium matrix composite Al2O3p/6061 subjected to diffusion welding were studied. The results are as follows: key factor affecting strength of welded joint is oxide in the weld zone. The existence of oxide in the welded joint not only hinders the diffusion of the matrix atoms, but also destroys the good interface between the matrix and the reinforced phase. The oxides turn into fine particles from film with increasing welding temperature, and the destroying effect on welded joint decreases, which increases the strength of the welded joint. On the basis of this, the diffusion welding of aluminium matrix composite Al2O3p/6061 was successfully realized.
文摘Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a nd mechanical properties. Electron Beam Welding (EBW) process has been found to be especially well suited in this area. Selection of the appropriate welding par ameters needs thorough investigations. These parameters include: preheat tempera ture (℃), welding current (I w), focusing current (I F), welding spee d (V), height between the gun and workpiece surface (H), scan width (S w) and shift distance (S). The present work aims firstly, setting the pr oper welding conditions to get sound joint between commercially pure copper (C10 200) and AISI 316 stainless steel plates 8 mm thickness. Secondly, investigate t he effect of Electron Beam (EB) shift, single-sided and double-sided welds on the mechanical, metallurgical and chemical properties of the weld bead. Due to t he high difference in thermal conductivity between copper and stainless steel, E lectron Beam (EB) was shifted towards copper with different values. These values were ranged from 0.3 to 0.9 mm in welding without preheating of copper plate an d from 0.1 to 0.4 mm with preheating. Number of joints were welded using variabl e EBW parameters in view to obtain the sound weld bead. These parameters are as follows: gradual reduction I w=51 to 49 mA, I F=845 mA, V=8 mm/sec , H=130 mm, S w=500 μm and S=0.4 mm. The investigation has shown t hat, the copper (C10200) plate must be preheated to get sound welded joint with AISI 316 stainless steel using the EBW process. The tensile fracture in all wel ded samples occurred in copper plate away from the weld bead. This reflects that the weld bead tensile strength is greater than the copper strength. The EB shif t has slight effect on hardness distribution through weld bead. The hardness val ue (H v) reduces in gradual manner from stainless steel hardness to copper one. The EB shift distance has no significant effect on the impact toughness.
文摘Al-6Mg alloy with trace Sc addition was prepared by means of melting-casting.The samples of the welded joints of Al-6Mg alloy with trace Sc addition were made by method of manual argon-arc welding.Neutral salt spray test was carried out by referring to GB/T10125-1997 and GB6384-1986 practice.Exfoliation testing was carried out in accordance with the method of Al-Mg alloy exfoliation corrosion test.The corrosion behaviors of the welded joints of AlMg alloy with high level of Mg and trace Sc addition were studied.The microstructures of the welded joints were observed by using optical microscope and transmission electron microscope.The corrosion resistance mechanism of the alloy was also involved.This work intended to determine if the welded joints of Al-6Mgalloy with trace Sc addition can have excellent corrosion resistance, when their strength are clearly improved.The results show that trace content of Sc refines the grains of alloys effectively, raises remarkably the corrosion resistance of the welded joints of Al-6Mg alloy with trace Sc addition.The corrosion resistance mechanisms are that there is free of continuous grain boundary precipitation or network which could be susceptible to corrosion in the microstructure of welded joints.
基金Supported by National 13th Five-Year Key Technologies R&D Program of China(Grant No.2016YFC0801902)National Natural Science Foundation of China(Grant No.11727803,11672356,52075490)Fundamental Research Funds for the Provincial Universities of Zhejiang(Grant No.RF-A2020010).
文摘In modern fossil and nuclear power plants,the components are subjected to creep,fatigue,and creep-fatigue(CF)due to frequent start-up and shut-down operations at high temperatures.The CF interaction on the in-service P92 steel welded joint was investigated by strain-controlled CF tests with different dwell times of 30,120,300,600 and 900 s at 650℃.Based on the observations of the fracture surface by scanning electron microscope(SEM),the character-istic microstructure of fatigue-induced damage was found for the CF specimens with short dwell times(30 and 120 s).The hardness,elastic modulus and creep deformation near the fracture edges of four typical CF specimens with 30,120,600 and 900 s dwell times were measured by nanoindentation.Compared to specimens with post-weld heat treatment(PWHT),lower hardness and creep strength were found for all CF specimens.In addition,significant reduc-tions in hardness,elastic modulus,and creep strength were measured near the fracture edges for the CF specimens with short dwell times compared to the PWHT specimens.Compared to PWHT specimens(0.007),the increased strain rate sensitivities(SRS)of 0.010 to 0.17 were estimated from secondary creep.The increased values of SRS indicate that the room temperature creeps behavior is strongly affected by the decrease in dislocation density after the CF tests.
文摘It is essential to understand the weld interface characteristics and mechanical properties of dissimilar joints to improve its quality.This study is aimed at exploring the properties of friction welded magnesium-titanium dissimilar joint using tensile testing coupled with digital image correlation,optical and scanning electron microscopy,x-ray diffraction and microhardness measurements.Microstructurally different regions such as contact zone,dynamic recrystallized zone,thermo-mechanically affected zone,and partially deformed zone in the magnesium side were observed.No discernible regions were observed in the titanium side,as it had not undergone any significant plastic deformation.Phase analysis indicated that the aluminium from the magnesium side diffused toward the weld interface and formed a thin continuous intermetallic layer by reacting with the titanium.Microhardness mapping showed a steep hardness gradient from the titanium to magnesium side.Critical analysis is done on the tensile characteristics of the specimen and the response of the local regions to the deformation process is mapped.
基金financially supported by the National Natural Science Foundation of China (No. 51105030)
文摘The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion(EXCO) solution. Electrochemical measurements(open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy), scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase(Al2Cu) after 2 h of immersion in EXCO solution.
基金supported by the National Key R&D Program of China(2022YFB2602901)the National Natural Science Foundation of China(No.52178405).
文摘The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track,and the design method of CWR and track structures on the beam ends are proposed.The results show that the unidirectional Rail Expansion Joints(REJ)need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force.Due to the bridge characteristics,there is no CWR fixed area on the kilometer-span bridge,and rail longitudinal force on the main span caused by bending loads needs to be concerned.The deformation of track on the beam end is complex,which is the weak area on the kilometer bridge,the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end,small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end.To improve the driving safety and comfort of beam end,the Sleeper-Supporting Apparatus(SSA)should be specially designed to ensure the uniform transition of track on beam ends.Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge,the dynamic response of trains and bridges under those loads needs to be attended to.
文摘With thick plates of 2219 high-strength alloy, the microstructures of welded joints with twin wire MIG welding were analyzed. Experimental results show that no hot crack was found in the weld due to discontinuous distribution of cocrystallization with low melting temperature, but porosity is serious in the first weld seam that is mainly composed of equiaxial grains with uneven sizes. As the poor position of the whole welded joint, fusion zone has big and coarse grains, uneven microstructures; In quenching zone, there exist a lot of soaked microstructures that cocrystallization with low melting temperature solute into matrix, thus strengthening the metal in this zone; In excessive aging zone, much more phases that distribute evenly will be separated from the matrix; Outside this zone, properties and microstructures of the metal are basically similar to matrix due to the relatively low temperature or unaffected heat in the zone during welding.
文摘The microstructures, the changing rule of carbon-enriched zone, the diffusion behaviors of elements C and Cr, and the carbide type of 0Cr6Mn13Ni10MoTi/1Cr5Mo dissimilar welded joints after aging at 500℃ for various times and after long-term service in technical practice were investigated by using the optical microscopy, electron probe microanalysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that in aging 0Cr6Mn13Ni10MoTi/1Cr5Mo dissimilar welded joints, the main carbides are M3C and a few carbides are M7C3 and M23C6. The M3C carbide decomposition and dissolution with increasing aging time or aging temperature and the anti-diffusion of C and Cr cause the decrease and disappearance of the carbon-enriched zone. The results are different from those of the A302/1Cr5Mo dissimilar welded joints in previous studies.
文摘The fatigue contrast tests of unload longitudinal direction corner joints as original welded and treated by ultrasonic peening of Q235B in various stress ratio are directed. The improvements of fatigue performance of unload longitudinal direction corner joints resulted by ultrasonic peening are studied. The effect pattern of stress ratio on fatigue performance of welded joints that are treated by ultrasonic peening is studied. As tests results indicate that: ① In the condition of stress ratio R= -1, the fatigue strength of specimen treated by ultrasonic peening is increased by 165% of that of the original welded specimen. And the fatigue life of specimen treated by ultrasonic peening is as much as 75～210 times of that of the latter. When R=0.1, the fatigue strength is increased by 87% and the fatigue life is extended by 21～29 times. When R= -0.5, the fatigue strength is increased by 123% and the fatigue life is extended by 42～59 times. When R=0.45, the fatigue strength is increased by 51% and the fatigue life is extended by 3～14 times. ② If the welded joints are treated by ultrasonic peening, the fatigue strength is no longer independent on the applied mean stress. The more the stress ratio R, the less the fatigue stress range which can be sustained by the joints is. ③ Whether the high value residual stress is in the joints or not, the dead load portion of the applied load must be considered in the design of the joints which should be treated by ultrasonic peening.
基金Project(2005CB623705) supported by the National Basic Research Program of China
文摘7A52 Al alloy plate aged at 105 ℃ for 8 h and then at 130 ℃ for 24 h was welded by means of TIG using Al- 6.3Mg-0.35Sc-0.1Zr-0.1Cr solder wire. Mechanical properties and microstructures of welded joint were studied. There are two obviously soft areas in the welded joint, welding seam and over-aging zone. The mechanical properties of welded joint are that σb is 358 MPa, σ0.2 is 238 MPa and δ5 is 6.6%. 75.6% of welding coefficient can be achieved. The addition of scandium leads to very significant grain refinement in the fusion zone, which results in a reduction in solidification cracking tendency. The solidification cracking isn’t observed.
