The superplastic deformation behavior and microstructure evolution of electron beam welded 5A90 aluminum lithium alloy were investigated. The results indicated that the electron beam weld joint had good superplasticit...The superplastic deformation behavior and microstructure evolution of electron beam welded 5A90 aluminum lithium alloy were investigated. The results indicated that the electron beam weld joint had good superplasticity under a suitable deformation condition. The elongation increased first and then decreased with increasing deformation temperature and initial strain rate,and the maximal elongation of 171.1% was obtained at the temperature of 450 ℃ and the strain rate of 5 × 10^(-3) s^(-1).The microstructure observation indicated that the fine equiaxed dendrite of weld bead transformed into coarse equiaxed in the initial stage( strain ε≤0.7),then refined in the later stage of superplastic deformation.The eutectic structure gradually decreased with the increase of strain. While the microstructure of HAZ was refined and equiaxed with the increase of strain.展开更多
Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm...Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy (SEM). Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone ( HAZ ). The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal (264. 50 MPa).展开更多
Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joi...Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.展开更多
SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properti...SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.展开更多
With the diversification of manufacture methods, joining the same materials with different states becomes indispensable in practical application. In present work, 6061 aluminum alloys with different states were welded...With the diversification of manufacture methods, joining the same materials with different states becomes indispensable in practical application. In present work, 6061 aluminum alloys with different states were welded by laser beam welding (LBW). The microstructures of welded joint, before and after heat treating, were investigated. The mechanical properties, such as the tensile properties and microhardness , were tested. And the fracture characteristic was observed by means of scanning electron microscope (SEM). The results show that the 6061 aluminum alloys have superior weldability and the microstructures are different significantly in different states. Besides, the grain boundaries of the joint microstructures become unclear after the heat treating. The strength and the elongations of welded joints could reach to those of the base metal. The tensile fracture occurs in the fusion zone and near 6061-0 alloy. And the fracture presents ductile rupture. Therefore, the LBW is an effective method for 6061 aluminum alloy.展开更多
The cast aluminum beam is a key structure for carrying the body-hung traction motor of a high-speed train;its fatigue property is fundamental for predicting the residual life and service mileage of the structure.To ch...The cast aluminum beam is a key structure for carrying the body-hung traction motor of a high-speed train;its fatigue property is fundamental for predicting the residual life and service mileage of the structure.To characterize the structural fatigue property,a finite element-based method is developed to compute the stress concentration factor,which is used to obtain the structural fatigue strength reduction factors.A full-scale fatigue test on the cast aluminum beam is designed and implemented for up to ten million cycles,and the corresponding finite element model of the beam is validated using the measured data of the gauges.The results show that the maximum stress concentration occurs at the fillet of the supporting seat,where the structural fatigue strength reduction factor is 2.45 and the calculated fatigue limit is 35.4 MPa.Moreover,no surface cracks are detected using the liquid penetrant test.Both the experimental and simulation results indicate that the cast aluminum beam can satisfy the service life requirements under the designed loading conditions.展开更多
Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding ...Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding of aluminum was analyzed and the effect of Al2O3 film on molten pool flow behavior and weld appearance was investigated. The results showed that the weld width of the specimen was enlarged by chemically cleaning. The solid Al2O3 film transformed into gaseous Al2O3 via the reaction with liquid aluminum at the temperature higher than 1 350 K was the main reason for the removal of the film. The weld width was narrowed down by the oxide film due to the inhibition of outward flow driven by the surface tension gradient and the drag force between the Al2O3 film and liquid Al. The weld penetration was reduced in the initial stage and then enhanced in the metastable stage.展开更多
This paper presents the formalism for absorbed dose determination to Aluminum in high-energy electron beams using Rhodotron accelerator. Depth dose curve for Aluminum at electron energy of 10 MeV was calculated. The c...This paper presents the formalism for absorbed dose determination to Aluminum in high-energy electron beams using Rhodotron accelerator. Depth dose curve for Aluminum at electron energy of 10 MeV was calculated. The calculated curve in the model as a function of the depth is compared to the experimental. The agreement of the final results remained well within the expected acceptable range. The calculated values of dose-to-Aluminum are completely fit with the measured values in the range of 0.07% for electron energy of 10 MeV.展开更多
Nitriding of surface of aluminum alloys was carried out with using an electron-beam-excited-plasma (EBEP) technique. The EBEP is sustained by electron impact ionization with energetic electron beam. Two kinds of subst...Nitriding of surface of aluminum alloys was carried out with using an electron-beam-excited-plasma (EBEP) technique. The EBEP is sustained by electron impact ionization with energetic electron beam. Two kinds of substrates, aluminum alloys AA5052 and AA5083, were exposed to the down flow of EBEP source at 843 K for 45min. The specimens were characterized with respect to following properties: crystallographic structure (XRD), morphology (SEM) and the cross sectional microstructures of the nitrided layer was observed using a scanning electron microscopy (SEM). There are some A12O3 particles on the surface of the nitrided AA5052 and AA5083. The A1N layers were formed on the substrates with the thickness of 4.5 fi m for AA5052 and 0.5 /z m for AA5083 . A relatively uniform nitrided surface layer composed of A1N can be observed on the AA5052 substrate. The grains size near the interfaces between the substrate and A1N layer were smaller than that near the surface. On the surface of A1N layer, the concentration of nitrogen was high and in the middle of A1N layer it had a constant concentration like the aluminum and the concentration was decreased with approaching to the interface. On the surface of nitrided AA5083, a uniform A1N layer was not formed as the reason for the high nitriding temperature.展开更多
To avoid the angular deformation of aluminum alloy T-joint weldments, a new method named welding with auxiliary heat source is proposed. The welding simulation is performed with the commercial finite element software ...To avoid the angular deformation of aluminum alloy T-joint weldments, a new method named welding with auxiliary heat source is proposed. The welding simulation is performed with the commercial finite element software Abaqus and FORTRAN programme encoding a special conical heat source with Gaussian volumetric distribution of flux. The influence of the local model on the temperature, residual stress, and welding deformation distributions is investigated. The findings show that angular deformation achieved through numerical computation completely consists with the experimental result which has proved the effectiveness of the finite element methods developed. Various measurements performed on small-scale welded test specimens provide a data base of experimental results that serves as a bench mark for qualification of the simulation result. Finally, the residual stress and strain states in a T-joint are predicted.展开更多
The restraint effects of pulse frequency and pulse duty cycle on the precipitates of harmful needle like Al 4C 3 phase were studied in CO 2 impulsed laser welding through the experiment on the SiC p/6063 composite, an...The restraint effects of pulse frequency and pulse duty cycle on the precipitates of harmful needle like Al 4C 3 phase were studied in CO 2 impulsed laser welding through the experiment on the SiC p/6063 composite, and the microstructures of the weld under the different process parameters (pulse time from 1 ms to 20 ms,duty cycle from 50% to 91%) were analyzed. In order to compare, CO 2 continuous laser was conducted under the same efficiency. The results demonstrate that the proper laser pulse frequency and duty cycle can restrain the formation of Al 4C 3 effectively. However, the burning loss of SiC is more serious and the fluidity of molten pool is less in continuous laser welding than in impulsed laser welding.展开更多
AlxIn1-xAs with 0.47&lex&le0.62 onto (100) oriented InP substrate was grown by molecular beam epitaxy (MBE) and characterized with X-ray double crystal diffraction, low temperature photoluminescence and an ele...AlxIn1-xAs with 0.47&lex&le0.62 onto (100) oriented InP substrate was grown by molecular beam epitaxy (MBE) and characterized with X-ray double crystal diffraction, low temperature photoluminescence and an electron probe. Results show their high qualities. Strain and residual stress were studied in detail.展开更多
In this paper, the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer crystalline quality are investigated. Crack-ftee AlN samples with various nucleation thicknesses are grown on ...In this paper, the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer crystalline quality are investigated. Crack-ftee AlN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The AlN crystalline quality is analysed by transmission electron microscope and x-ray diffraction (XRD) rocking curves in both (002) and (102) planes. The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope. A critical nucleation thickness for realising high quality AlN films is found. When the nucleation thickness is above a certain value, the (102) XRD full width at half maximum (FWHM) of AlN bulk increases with nucleation thickness increasing, whereas the (002) XRD FWHM shows an opposite trend. These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AlN main layer growth.展开更多
基金Project (51465042) supported by the National Natural Science Foundation of China
文摘The superplastic deformation behavior and microstructure evolution of electron beam welded 5A90 aluminum lithium alloy were investigated. The results indicated that the electron beam weld joint had good superplasticity under a suitable deformation condition. The elongation increased first and then decreased with increasing deformation temperature and initial strain rate,and the maximal elongation of 171.1% was obtained at the temperature of 450 ℃ and the strain rate of 5 × 10^(-3) s^(-1).The microstructure observation indicated that the fine equiaxed dendrite of weld bead transformed into coarse equiaxed in the initial stage( strain ε≤0.7),then refined in the later stage of superplastic deformation.The eutectic structure gradually decreased with the increase of strain. While the microstructure of HAZ was refined and equiaxed with the increase of strain.
基金This research was supported by Major Subject Foundation of Beijing University of Technology
文摘Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy (SEM). Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone ( HAZ ). The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal (264. 50 MPa).
文摘Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.
基金Project was supported by the National Nature Science Foundation of China(51375115).
文摘SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.
文摘With the diversification of manufacture methods, joining the same materials with different states becomes indispensable in practical application. In present work, 6061 aluminum alloys with different states were welded by laser beam welding (LBW). The microstructures of welded joint, before and after heat treating, were investigated. The mechanical properties, such as the tensile properties and microhardness , were tested. And the fracture characteristic was observed by means of scanning electron microscope (SEM). The results show that the 6061 aluminum alloys have superior weldability and the microstructures are different significantly in different states. Besides, the grain boundaries of the joint microstructures become unclear after the heat treating. The strength and the elongations of welded joints could reach to those of the base metal. The tensile fracture occurs in the fusion zone and near 6061-0 alloy. And the fracture presents ductile rupture. Therefore, the LBW is an effective method for 6061 aluminum alloy.
基金Supported by the National Natural Science Foundation of China(Grant No.51475036)the International Cooperation and Exchange of the National Natural Science Foundation of China(Grant No.51711530034).
文摘The cast aluminum beam is a key structure for carrying the body-hung traction motor of a high-speed train;its fatigue property is fundamental for predicting the residual life and service mileage of the structure.To characterize the structural fatigue property,a finite element-based method is developed to compute the stress concentration factor,which is used to obtain the structural fatigue strength reduction factors.A full-scale fatigue test on the cast aluminum beam is designed and implemented for up to ten million cycles,and the corresponding finite element model of the beam is validated using the measured data of the gauges.The results show that the maximum stress concentration occurs at the fillet of the supporting seat,where the structural fatigue strength reduction factor is 2.45 and the calculated fatigue limit is 35.4 MPa.Moreover,no surface cracks are detected using the liquid penetrant test.Both the experimental and simulation results indicate that the cast aluminum beam can satisfy the service life requirements under the designed loading conditions.
基金supported by the International S&T Cooperation Program of China(Grant No.2011DFR60)
文摘Aluminum specimens with and without chemically cleaning were welded by electron beam to investigate the effect of Al2O3 film on weld appearance. The removal mechanism of Al2O3 film during vacuum electron beam welding of aluminum was analyzed and the effect of Al2O3 film on molten pool flow behavior and weld appearance was investigated. The results showed that the weld width of the specimen was enlarged by chemically cleaning. The solid Al2O3 film transformed into gaseous Al2O3 via the reaction with liquid aluminum at the temperature higher than 1 350 K was the main reason for the removal of the film. The weld width was narrowed down by the oxide film due to the inhibition of outward flow driven by the surface tension gradient and the drag force between the Al2O3 film and liquid Al. The weld penetration was reduced in the initial stage and then enhanced in the metastable stage.
文摘This paper presents the formalism for absorbed dose determination to Aluminum in high-energy electron beams using Rhodotron accelerator. Depth dose curve for Aluminum at electron energy of 10 MeV was calculated. The calculated curve in the model as a function of the depth is compared to the experimental. The agreement of the final results remained well within the expected acceptable range. The calculated values of dose-to-Aluminum are completely fit with the measured values in the range of 0.07% for electron energy of 10 MeV.
文摘Nitriding of surface of aluminum alloys was carried out with using an electron-beam-excited-plasma (EBEP) technique. The EBEP is sustained by electron impact ionization with energetic electron beam. Two kinds of substrates, aluminum alloys AA5052 and AA5083, were exposed to the down flow of EBEP source at 843 K for 45min. The specimens were characterized with respect to following properties: crystallographic structure (XRD), morphology (SEM) and the cross sectional microstructures of the nitrided layer was observed using a scanning electron microscopy (SEM). There are some A12O3 particles on the surface of the nitrided AA5052 and AA5083. The A1N layers were formed on the substrates with the thickness of 4.5 fi m for AA5052 and 0.5 /z m for AA5083 . A relatively uniform nitrided surface layer composed of A1N can be observed on the AA5052 substrate. The grains size near the interfaces between the substrate and A1N layer were smaller than that near the surface. On the surface of A1N layer, the concentration of nitrogen was high and in the middle of A1N layer it had a constant concentration like the aluminum and the concentration was decreased with approaching to the interface. On the surface of nitrided AA5083, a uniform A1N layer was not formed as the reason for the high nitriding temperature.
基金This work was supported by the National Natural Science Foundation of China ( Grant No. 50305035 ).
文摘To avoid the angular deformation of aluminum alloy T-joint weldments, a new method named welding with auxiliary heat source is proposed. The welding simulation is performed with the commercial finite element software Abaqus and FORTRAN programme encoding a special conical heat source with Gaussian volumetric distribution of flux. The influence of the local model on the temperature, residual stress, and welding deformation distributions is investigated. The findings show that angular deformation achieved through numerical computation completely consists with the experimental result which has proved the effectiveness of the finite element methods developed. Various measurements performed on small-scale welded test specimens provide a data base of experimental results that serves as a bench mark for qualification of the simulation result. Finally, the residual stress and strain states in a T-joint are predicted.
文摘The restraint effects of pulse frequency and pulse duty cycle on the precipitates of harmful needle like Al 4C 3 phase were studied in CO 2 impulsed laser welding through the experiment on the SiC p/6063 composite, and the microstructures of the weld under the different process parameters (pulse time from 1 ms to 20 ms,duty cycle from 50% to 91%) were analyzed. In order to compare, CO 2 continuous laser was conducted under the same efficiency. The results demonstrate that the proper laser pulse frequency and duty cycle can restrain the formation of Al 4C 3 effectively. However, the burning loss of SiC is more serious and the fluidity of molten pool is less in continuous laser welding than in impulsed laser welding.
文摘AlxIn1-xAs with 0.47&lex&le0.62 onto (100) oriented InP substrate was grown by molecular beam epitaxy (MBE) and characterized with X-ray double crystal diffraction, low temperature photoluminescence and an electron probe. Results show their high qualities. Strain and residual stress were studied in detail.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60536020 and 60723002)the National Basic Research Program of China (Grant Nos. 2006CB302800 and 2006CB921106)+1 种基金the National High Technology Research and Development Program for Advanced Materials of China (Grant No. 2006AA03A105)the Major Project of Beijing Municipal Science and Technology Commission,China (Grant No. D0404003040321)
文摘In this paper, the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer crystalline quality are investigated. Crack-ftee AlN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The AlN crystalline quality is analysed by transmission electron microscope and x-ray diffraction (XRD) rocking curves in both (002) and (102) planes. The surface profiles of nucleation layer with different thicknesses after in-situ annealing are also analysed by atomic force microscope. A critical nucleation thickness for realising high quality AlN films is found. When the nucleation thickness is above a certain value, the (102) XRD full width at half maximum (FWHM) of AlN bulk increases with nucleation thickness increasing, whereas the (002) XRD FWHM shows an opposite trend. These phenomena can be attributed to the characteristics of nucleation islands and the evolution of crystal grains during AlN main layer growth.