The laser wire （LW） method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this ...The laser wire （LW） method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this paper, we present an improved design of high repetition LW system for high average power free electron lasers （HAP FELs） and energy recovery linacs （ERLs）. This improved LW utilizes the excess power of the photocathode drive laser, thus making itself much cheaper and simpler. The system main parameters are optimized with numerical calculations and Monte Carlo simulations, indicating that resolutions would be better than 100 ~m and scanning time less than 1 minute. Status of the experiment preparation is also presented.展开更多
With preheating wire by resistance heat, laser hot wire welding improves process stability and wire deposition efficiency, which gives broad potential applications in sugracing and narrow gap welding. It is a critical...With preheating wire by resistance heat, laser hot wire welding improves process stability and wire deposition efficiency, which gives broad potential applications in sugracing and narrow gap welding. It is a critical issue to control the temperature of preheated wire in this process. The temperature which is so high that the wire fuses outside molten pool or so low that the wire cannot melt timely in the molten pool, results in poor wire transfer stability and bad weld formation. This paper is purposed to calculate the wire temperature for the prediction of wire transfer behavior under various welding parameters. A heat conduction model is set up. Heat sources of the wire include resistance heat and reflected laser, and the heat source of molten pool is laser. The calculated temperature of wire part outside the molten pool is verified by infrared ratio temperature measurement. The calculated temperature of wire part in the molten pool is verified by measurement of the molten pool size. Analyzing the wire temperature and welding process observed by the high speed video imaging, the temperature criteria of wire transfer behaviors are obtained. Thus, numerical simulation of the wire temperature can be used to predict wire transfer behaviors in laser hot wire welding.展开更多
Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that th...Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that the weld appearance can be effectively improved when using laser welding with filler wire. The microhardness and tensile strength of joints are almost the same us those of the base metal when ER AZ31 or ER AZ61 wire is adopted. However, when the filler wire of ER 5356 aluminum alloy is used, the mechanical properties of flints become worse. For ER AZ31 and ER AZ61 filler wires, the microstructure of weld zone slws small dendrite grains. In comparison, for ER 5356 filler wire, the weld shows a structure of snowy dendrites and many intermetallic compounds and eutectic phases distribute in the dendrites. These intermetallic constituents with low melting point increase the tendency of hot crack and result in fiagile joint properties. Therefore, ER AZ31 and ER AZ61 wire are more suitable filler material than ER 5356 for CO2 laser welding of AZ31 magnesium alloys.展开更多
The process properties and interface behavior of CO_2 laser brazing with automatic wire feed for galvanized steel sheets were investigated, in which the brazing filler metal was CuSi3 and no flux was used. As to the a...The process properties and interface behavior of CO_2 laser brazing with automatic wire feed for galvanized steel sheets were investigated, in which the brazing filler metal was CuSi3 and no flux was used. As to the appearance quality of the brazing seams, the roles of the processing parameters, such as brazing speed, wire feeding rate, inclination and feeding direction of the wire, laser power, spot diameter and heating position, were assessed. The further investigation indicates that the behavior of the active elements Si, Mn and Zn are significantly influenced by energy input. At the interface, the microstructure of the base metal was composed of columnar crystals and the acicular α solid solution was found on the filler metal side.展开更多
The temperature fields in laser ＋ GMAW-P hybrid welding for different laser-wire distances in quasi-steady state were calculated using an developed combined heat source model, and the influence of laser-wire distance...The temperature fields in laser ＋ GMAW-P hybrid welding for different laser-wire distances in quasi-steady state were calculated using an developed combined heat source model, and the influence of laser-wire distance on them was analyzed. The results show tbat, at a low level of arc power, the temperature profiles caused by laser and arc energy respecively cannot couple well when the laser-wire distance reaches 4 mm, a trend of separation between them beginning to take place. In the case of high arc power, both the critical laser-wire distance and HAZ width increase.展开更多
CO2 laser welding aluminum alloy with filler wire was studied. The results indicate that the problems in CO2 laser welding of Al alloy, such as bad appearance of weld, easily excessive penetration and low strength, ca...CO2 laser welding aluminum alloy with filler wire was studied. The results indicate that the problems in CO2 laser welding of Al alloy, such as bad appearance of weld, easily excessive penetration and low strength, can be improved effectively by using laser welding with filler wire, and the maximum tensile strength of weld can reach 94% for the base metal. It also can be found that, the linear energy have great influence on the microstructure and mechanical properties of the joint. As the heat input increases, the cellular fir-tree crystals in the weld zone become sparse and the form of tensile fracture transforms from gliding fracture to brittle fracture.展开更多
The weld appearance, deposition rate, welding efficiency, stability of arc, laser keyhole characteristic, and weld property were studied by using a novel laser-MIG hybrid welding process with filling wire of aluminum ...The weld appearance, deposition rate, welding efficiency, stability of arc, laser keyhole characteristic, and weld property were studied by using a novel laser-MIG hybrid welding process with filling wire of aluminum alloy. The results were also compared with those by conventional laser-MIG hybrid welding process. It was found that with the suitable process parameters this novel welding process for aluminum alloy was stable and final weld bead had fine appearance. Compared to conventional laser-MIG hybrid welding process, during this novel welding process the stability of arc, the laser keyhole characteristic and the weld property were similar, while the keyhole cycle frequency and keyhole opening area had differences of 1.23% and 15.34%, respectively, and the welding efficiency increased by about 31% without increasing heat input.展开更多
Formation of copper wiring on a polyimide film by laser irradiation to a stable copper-complex film consisting of glyoxylic acid copper complex and methylamine copper complex in air has been investigated. A stable met...Formation of copper wiring on a polyimide film by laser irradiation to a stable copper-complex film consisting of glyoxylic acid copper complex and methylamine copper complex in air has been investigated. A stable metallic copper on the polyimide film was precipitated even in air. Since this copper was generated only in the laser-irradiated parts, direct patterning of copper wiring was possible. It was also found that copper was precipitated by electroless copper plating on the laser-deposited copper wiring and it was possible to thicken the copper wiring by this precipitation. The resistivity of the copper wiring was almost the same as that of the bulk of metallic copper. The developed method—combining laser irradiation to a copper-complex-coated film and electroless copper plating—enables the high-speed deposition of fine copper wiring on a polyimide film in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring without high vacuum facility and heat-treatment under inert gas.展开更多
Preparation of a glyoxylic acid copper complex and fabrication of fine copper wire by CO2 laser irradiation in air to a thin film of that complex have been investigated. Irradiating laser to the complex thin film spin...Preparation of a glyoxylic acid copper complex and fabrication of fine copper wire by CO2 laser irradiation in air to a thin film of that complex have been investigated. Irradiating laser to the complex thin film spin-coated on a glass substrate, thin film of metallic copper was fabricated in areas that were subjected to laser irradiation in air. The thickness of this thin copper film was approx. 30 to 40 nm, and as non-irradiated areas were etched and removed by a soluble solvent of the copper complex, fine copper wire with 200 μm width was formed by laser direct patterning. The resistivity of this thin copper film depended on the irradiation intensity of the laser and was 3.0 × 10–5 Ω·cm at 12 W intensity (sweep speed: 20 mm/s). This method enables the high-speed deposition of copper wiring in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring.展开更多
In laser ＋ P-GMA hybrid welding, laser-wire distance is an important parameter to describe the distance from laser spot to the center of the pulsed gas metal arc. The experiments results show that the optimal laser-w...In laser ＋ P-GMA hybrid welding, laser-wire distance is an important parameter to describe the distance from laser spot to the center of the pulsed gas metal arc. The experiments results show that the optimal laser-wire distance with the deepest weld penetration increases with welding current and laser power being increased and decreases with welding speed being increased. Welding current, laser power and welding speed determine the hybrid welding heat input in laser ＋ arc hybrid welding process, so there is a correlation between the optimal laser-wire distanee and the hybrid heat input welding parameters for the deepest weld penetration： the optimal laser-wire distance increases with the heat input being increased. The positive correlation between the optimal laser-wire distance and the hybrid welding heat input is induced by the characteristics of the limited influence of P-GMA welding process on laser transmission and the dependence of weld penetration of hybrid welding on laser power.展开更多
The Al-Cu-Li alloy is welded by using laser beam welding,and the welding wire ER4043 is used as filler metal. The microstructure and mechanical property of welded joints are systematically investigated. Microstructure...The Al-Cu-Li alloy is welded by using laser beam welding,and the welding wire ER4043 is used as filler metal. The microstructure and mechanical property of welded joints are systematically investigated. Microstructure analyses show that the fusion zone is mainly composed of α-Al matrix phase and some strengthening phases including T,δ’,θ’,β’ and T1,etc. During welding,the weld formation and joint quality are obviously improved by the addition of Al-Si filler wire. The measurements of mechanical property indicate that,compared with that of the base metal(BM), the microhardness in the weld zone is decreased to a certain extent. Under the appropriate welding parameters,the tensile strength of welded joint reaches 369.4 MPa,which is 67.8% of that of the BM. There are many dimples on the joint fracture surface,and it mainly presents the fracture characteristic of dimple aggregation.展开更多
The laser-cladding technique for welding of bridge wires is reported for the first time.The essen- tial feature of this technique different from the cur- rent methods is the realization of mutual melting of workpieces...The laser-cladding technique for welding of bridge wires is reported for the first time.The essen- tial feature of this technique different from the cur- rent methods is the realization of mutual melting of workpieces.Thus the stability of products is im- proved in an order of magnitude.The main points of the technique and the microanalyses of the weld- ing spot and other features are given.The technique presented is a novel method of welding between tiny piece and workpiece of different sizes and proper- ties.展开更多
The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The me...The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaC1 solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical compo- nents and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat- affected zone with a compact protective film.展开更多
Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produce...Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by WAAM.Calibrations for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.展开更多
The characteristics of weld shape,microstructure,mechanical properties and defects of 5A90 Al-Li alloy joint by laser welding(LBW)and laser welding with filler wire(LWFW)were studied and analyzed.The results indicated...The characteristics of weld shape,microstructure,mechanical properties and defects of 5A90 Al-Li alloy joint by laser welding(LBW)and laser welding with filler wire(LWFW)were studied and analyzed.The results indicated that the microstructure of joint by LWFW was fine-grained layer and the equiaxed grain in most of seams,which were similar to the joint by LBW.Compared with the joint by LBW,the microstructure of joint by LWFW tended to fine,and the range of the columnar crystals zone was prone to decrease.The Microhardness of the joint by LWFW(92.57HV0.2)was lower than that by LBW(95.65HV0.2),but the uniformity was better.The ultimate tensile strength of the joint by LWFW was lower than that by LBW slightly,which reached to 73.03%and 79.22%of the base metal respectively.However,the elongation of the LWFW joint was higher than that of the LBW joint significantly,which reached to 38.65%and 20.38%of the base metal respectively.The microstructure and mechanical properties of 5A90 Al-Li alloy by LWFW were better than that by LBW.The defects of joint were mainly forming defects which were caused by improper parameters and porosity inside the joint,which was caused by uncleaned surface and incomplete penetration.展开更多
Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fi...Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fiber rods obtained directly from LHPG method are semiconductive and after heat treatment at temperature range from 780 to 870℃,they transformed into superconductive wires.Triple junctions and sharp grain boundary exist in the sample.HREM studies showed the intergrowth of (010) and (110),the occasional missing of CaCuO_2 layer in the 2212 phase.展开更多
We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures....We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.展开更多
A single particle magneto-confined in a one-dimensional （1D） quantum wire experiences a harmonic potential, and imposing a sharply focused laser beam on an appropriate site shapes a δ potential. The theoretical inv...A single particle magneto-confined in a one-dimensional （1D） quantum wire experiences a harmonic potential, and imposing a sharply focused laser beam on an appropriate site shapes a δ potential. The theoretical investigation has demonstrated that for a sufficiently strong δ pulse the quantum motional stationary state of the particle is one of the eigenstates of the free harmonic oscillator, and it is determined by the site of the laser beam uniquely, namely a quantum state is admissible if and only if the laser site is one of its nodes. The numerical computation shows that all the nodes of the lower energy states with quantum numbers n ≤ 20, except the coordinate origin, are mutually different. So we can manipulate the multiphoton transitions between the quantum states by adjusting the position of the laser δ pulse and realize the transition from an unknown higher excitation state to a required lower energy state.展开更多
文摘The laser wire （LW） method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this paper, we present an improved design of high repetition LW system for high average power free electron lasers （HAP FELs） and energy recovery linacs （ERLs）. This improved LW utilizes the excess power of the photocathode drive laser, thus making itself much cheaper and simpler. The system main parameters are optimized with numerical calculations and Monte Carlo simulations, indicating that resolutions would be better than 100 ~m and scanning time less than 1 minute. Status of the experiment preparation is also presented.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 51005125 ） and National Basic Research Program of China （Grant No. 2011CB013404）.
文摘With preheating wire by resistance heat, laser hot wire welding improves process stability and wire deposition efficiency, which gives broad potential applications in sugracing and narrow gap welding. It is a critical issue to control the temperature of preheated wire in this process. The temperature which is so high that the wire fuses outside molten pool or so low that the wire cannot melt timely in the molten pool, results in poor wire transfer stability and bad weld formation. This paper is purposed to calculate the wire temperature for the prediction of wire transfer behavior under various welding parameters. A heat conduction model is set up. Heat sources of the wire include resistance heat and reflected laser, and the heat source of molten pool is laser. The calculated temperature of wire part outside the molten pool is verified by infrared ratio temperature measurement. The calculated temperature of wire part in the molten pool is verified by measurement of the molten pool size. Analyzing the wire temperature and welding process observed by the high speed video imaging, the temperature criteria of wire transfer behaviors are obtained. Thus, numerical simulation of the wire temperature can be used to predict wire transfer behaviors in laser hot wire welding.
文摘Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that the weld appearance can be effectively improved when using laser welding with filler wire. The microhardness and tensile strength of joints are almost the same us those of the base metal when ER AZ31 or ER AZ61 wire is adopted. However, when the filler wire of ER 5356 aluminum alloy is used, the mechanical properties of flints become worse. For ER AZ31 and ER AZ61 filler wires, the microstructure of weld zone slws small dendrite grains. In comparison, for ER 5356 filler wire, the weld shows a structure of snowy dendrites and many intermetallic compounds and eutectic phases distribute in the dendrites. These intermetallic constituents with low melting point increase the tendency of hot crack and result in fiagile joint properties. Therefore, ER AZ31 and ER AZ61 wire are more suitable filler material than ER 5356 for CO2 laser welding of AZ31 magnesium alloys.
文摘The process properties and interface behavior of CO_2 laser brazing with automatic wire feed for galvanized steel sheets were investigated, in which the brazing filler metal was CuSi3 and no flux was used. As to the appearance quality of the brazing seams, the roles of the processing parameters, such as brazing speed, wire feeding rate, inclination and feeding direction of the wire, laser power, spot diameter and heating position, were assessed. The further investigation indicates that the behavior of the active elements Si, Mn and Zn are significantly influenced by energy input. At the interface, the microstructure of the base metal was composed of columnar crystals and the acicular α solid solution was found on the filler metal side.
文摘The temperature fields in laser ＋ GMAW-P hybrid welding for different laser-wire distances in quasi-steady state were calculated using an developed combined heat source model, and the influence of laser-wire distance on them was analyzed. The results show tbat, at a low level of arc power, the temperature profiles caused by laser and arc energy respecively cannot couple well when the laser-wire distance reaches 4 mm, a trend of separation between them beginning to take place. In the case of high arc power, both the critical laser-wire distance and HAZ width increase.
文摘CO2 laser welding aluminum alloy with filler wire was studied. The results indicate that the problems in CO2 laser welding of Al alloy, such as bad appearance of weld, easily excessive penetration and low strength, can be improved effectively by using laser welding with filler wire, and the maximum tensile strength of weld can reach 94% for the base metal. It also can be found that, the linear energy have great influence on the microstructure and mechanical properties of the joint. As the heat input increases, the cellular fir-tree crystals in the weld zone become sparse and the form of tensile fracture transforms from gliding fracture to brittle fracture.
基金supported by the Key Science and Technology of Jilin Province(Grant No.20140204070GX)
文摘The weld appearance, deposition rate, welding efficiency, stability of arc, laser keyhole characteristic, and weld property were studied by using a novel laser-MIG hybrid welding process with filling wire of aluminum alloy. The results were also compared with those by conventional laser-MIG hybrid welding process. It was found that with the suitable process parameters this novel welding process for aluminum alloy was stable and final weld bead had fine appearance. Compared to conventional laser-MIG hybrid welding process, during this novel welding process the stability of arc, the laser keyhole characteristic and the weld property were similar, while the keyhole cycle frequency and keyhole opening area had differences of 1.23% and 15.34%, respectively, and the welding efficiency increased by about 31% without increasing heat input.
文摘Formation of copper wiring on a polyimide film by laser irradiation to a stable copper-complex film consisting of glyoxylic acid copper complex and methylamine copper complex in air has been investigated. A stable metallic copper on the polyimide film was precipitated even in air. Since this copper was generated only in the laser-irradiated parts, direct patterning of copper wiring was possible. It was also found that copper was precipitated by electroless copper plating on the laser-deposited copper wiring and it was possible to thicken the copper wiring by this precipitation. The resistivity of the copper wiring was almost the same as that of the bulk of metallic copper. The developed method—combining laser irradiation to a copper-complex-coated film and electroless copper plating—enables the high-speed deposition of fine copper wiring on a polyimide film in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring without high vacuum facility and heat-treatment under inert gas.
文摘Preparation of a glyoxylic acid copper complex and fabrication of fine copper wire by CO2 laser irradiation in air to a thin film of that complex have been investigated. Irradiating laser to the complex thin film spin-coated on a glass substrate, thin film of metallic copper was fabricated in areas that were subjected to laser irradiation in air. The thickness of this thin copper film was approx. 30 to 40 nm, and as non-irradiated areas were etched and removed by a soluble solvent of the copper complex, fine copper wire with 200 μm width was formed by laser direct patterning. The resistivity of this thin copper film depended on the irradiation intensity of the laser and was 3.0 × 10–5 Ω·cm at 12 W intensity (sweep speed: 20 mm/s). This method enables the high-speed deposition of copper wiring in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring.
基金Supported by the key project of Natural Science Foundation of Heilongjiang Province （ZJG0601 and the National Key Technologies Research and Development Program of China during the 11^th Five-Year Plan Period （2006BAFO4B10）.
文摘In laser ＋ P-GMA hybrid welding, laser-wire distance is an important parameter to describe the distance from laser spot to the center of the pulsed gas metal arc. The experiments results show that the optimal laser-wire distance with the deepest weld penetration increases with welding current and laser power being increased and decreases with welding speed being increased. Welding current, laser power and welding speed determine the hybrid welding heat input in laser ＋ arc hybrid welding process, so there is a correlation between the optimal laser-wire distanee and the hybrid heat input welding parameters for the deepest weld penetration： the optimal laser-wire distance increases with the heat input being increased. The positive correlation between the optimal laser-wire distance and the hybrid welding heat input is induced by the characteristics of the limited influence of P-GMA welding process on laser transmission and the dependence of weld penetration of hybrid welding on laser power.
基金supported by the Key Research and Development Program of Zhenjiang City(No. GY2019004).
文摘The Al-Cu-Li alloy is welded by using laser beam welding,and the welding wire ER4043 is used as filler metal. The microstructure and mechanical property of welded joints are systematically investigated. Microstructure analyses show that the fusion zone is mainly composed of α-Al matrix phase and some strengthening phases including T,δ’,θ’,β’ and T1,etc. During welding,the weld formation and joint quality are obviously improved by the addition of Al-Si filler wire. The measurements of mechanical property indicate that,compared with that of the base metal(BM), the microhardness in the weld zone is decreased to a certain extent. Under the appropriate welding parameters,the tensile strength of welded joint reaches 369.4 MPa,which is 67.8% of that of the BM. There are many dimples on the joint fracture surface,and it mainly presents the fracture characteristic of dimple aggregation.
文摘The laser-cladding technique for welding of bridge wires is reported for the first time.The essen- tial feature of this technique different from the cur- rent methods is the realization of mutual melting of workpieces.Thus the stability of products is im- proved in an order of magnitude.The main points of the technique and the microanalyses of the weld- ing spot and other features are given.The technique presented is a novel method of welding between tiny piece and workpiece of different sizes and proper- ties.
基金financially supported by the National Natural Science Foundation of China (Grant Number: 51505010)Beijing Natural Science Foundation (Grant Number: 2152007)
文摘The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaC1 solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical compo- nents and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat- affected zone with a compact protective film.
基金Supported by National Natural Science Foundation of China(Grant Nos.51505394,61573293)Key Technologies R&D Program of Sichuan Province of China(Grant No.2015GZ0305)
文摘Wire and arc additive manufacturing(WAAM) shows a great promise for fabricating fully dense metal parts by means of melting materials in layers using a welding heat source. However, due to a large layer height produced in WAAM, an unsatisfactory surface roughness of parts processed by this technology has been a key issue. A methodology based on laser vision sensing is proposed to quantitatively calculate the surface roughness of parts deposited by WAAM.Calibrations for a camera and a laser plane of the optical system are presented. The reconstruction precision of the laser vision system is verified by a standard workpiece. Additionally, this determination approach is utilized to calculate the surface roughness of a multi-layer single-pass thin-walled part. The results indicate that the optical measurement approach based on the laser vision sensing is a simple and effective way to characterize the surface roughness of parts deposited by WAAM. The maximum absolute error is less than 0.15 mm. The proposed research provides the foundation for surface roughness optimization with different process parameters.
文摘The characteristics of weld shape,microstructure,mechanical properties and defects of 5A90 Al-Li alloy joint by laser welding(LBW)and laser welding with filler wire(LWFW)were studied and analyzed.The results indicated that the microstructure of joint by LWFW was fine-grained layer and the equiaxed grain in most of seams,which were similar to the joint by LBW.Compared with the joint by LBW,the microstructure of joint by LWFW tended to fine,and the range of the columnar crystals zone was prone to decrease.The Microhardness of the joint by LWFW(92.57HV0.2)was lower than that by LBW(95.65HV0.2),but the uniformity was better.The ultimate tensile strength of the joint by LWFW was lower than that by LBW slightly,which reached to 73.03%and 79.22%of the base metal respectively.However,the elongation of the LWFW joint was higher than that of the LBW joint significantly,which reached to 38.65%and 20.38%of the base metal respectively.The microstructure and mechanical properties of 5A90 Al-Li alloy by LWFW were better than that by LBW.The defects of joint were mainly forming defects which were caused by improper parameters and porosity inside the joint,which was caused by uncleaned surface and incomplete penetration.
文摘Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm^2 (78K, OT;cross area=1.04 mm^2).The fiber rods obtained directly from LHPG method are semiconductive and after heat treatment at temperature range from 780 to 870℃,they transformed into superconductive wires.Triple junctions and sharp grain boundary exist in the sample.HREM studies showed the intergrowth of (010) and (110),the occasional missing of CaCuO_2 layer in the 2212 phase.
基金Project supported by the National Natural Science Foundation of China （Grant No 10574042）, and the Hunan Provincial Natural Science Foundation of China （Grant No 06JJ2097）.
文摘We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.
基金Project supported by the National Natural Science Foundation of China （Grant No 10575034）, and the Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics of China （Grant No T152504）.
文摘A single particle magneto-confined in a one-dimensional （1D） quantum wire experiences a harmonic potential, and imposing a sharply focused laser beam on an appropriate site shapes a δ potential. The theoretical investigation has demonstrated that for a sufficiently strong δ pulse the quantum motional stationary state of the particle is one of the eigenstates of the free harmonic oscillator, and it is determined by the site of the laser beam uniquely, namely a quantum state is admissible if and only if the laser site is one of its nodes. The numerical computation shows that all the nodes of the lower energy states with quantum numbers n ≤ 20, except the coordinate origin, are mutually different. So we can manipulate the multiphoton transitions between the quantum states by adjusting the position of the laser δ pulse and realize the transition from an unknown higher excitation state to a required lower energy state.
