The microstructure, phase composition and cold shut defect of thick titanium alloy electron beam welded joint were studied. The results showed that the microstructure of weld zone was composed of α′ phase; the heat ...The microstructure, phase composition and cold shut defect of thick titanium alloy electron beam welded joint were studied. The results showed that the microstructure of weld zone was composed of α′ phase; the heat affected zone was divided into fine-grained zone and coarse-grained zone, the microstructure of fine-grained zone was primary α phase ＋ β phase ＋ equiaxed α phase, and the microstructure of coarse-grained zone was primary α phase ＋ acicular α′ phase; the microstructure of base metal zone basically consisted of primary α phase, and a small amount of residual β phase sprinkled. The forming. reason of cold shut was analyzed, and the precaution of cold shut was proposed.展开更多
Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint...Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint was predicted by finite element （FE） method, while the structural morphology of distinctive zones was obtained through metallographic experiments. The highest principal stress made the symmetric face of the joint most sensitive to tensile cracks under service conditions. Whereas, the boundaries between the weld seam and the base plates were sensitive to cracks because the equivalent von Mises stress was the highest when the first interpass cooling was finished. The third weld pass and the inter-pass remelted zones exhibited the modest mechanical performances as a result of the coarse grain and coarse grain boundary, respectively. The most vulnerable zones were regarded to be the crossed parts between the zones identified by numerical and experimental methods.展开更多
Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were ...Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were applied. The minimum critical thickness reduction to begin cold weld was specified as 70% which equals 0.1630 critical rolling shape factors. The bimetallic strips were treated by diffusion annealing at 400 ~C and various annealing time. The A1/Ag interface of strips was observed by scanning electron microscope to investigate the formation of hard and brittle probable phases. The effect of anneal time on diffusion distance and phase transformation was also analysed by EDS analysis and line scan. A diffusion region along the interface in the Ag side was observed and its width increased with prolonging annealing time. Some 8 phases were detected close to the interface after anneal treating for 3 h and 8 phase was thicker and more continuous by increasing annealing time. The microhardness measurement showed that in spite of formation of 8 phase due to diffusion annealing, the interface hardness was reduced.展开更多
The interfacial bonding of Ag-Cu (they are limited soluble) formed by the technology of cold pressure welding was discussed from the point of metallurgic view in this paper. Meanwhile, tensile test and microscopic tes...The interfacial bonding of Ag-Cu (they are limited soluble) formed by the technology of cold pressure welding was discussed from the point of metallurgic view in this paper. Meanwhile, tensile test and microscopic test were adopted for studying the state of interfacial bonding, suggesting that the joint of Ag-Cu has not only strong welding joint but also atomic diffusion on the interface. For Ag-Cu, the interaction of dislocation caused by plastic deformation will cause the strain and the vibration of microconstructer defects, accompanied by emitting energy. The energy increases the atomic action and the amplitude of atomic vibration, and the result is that the atom can diffuse to several lattice parameters deep from interface to inner metals. Therefore, under the condition of chemical potential gradient, the special technique, cold pressure welding rather than basic requirements of diffusion should be taken into account. During the cold pressure welding, plastic deformation plays an important role for it causes the metals′ displacement, crystal defects, further activates the surface atoms. Finally, the fracture of atomic bonding leads to the atomic exchange and diffusion between the new metals′ surfaces.In other words the metals Ag,Cu can achieve solidate bonding by cold pressure welding accompanied by the atomic diffusion. Moreover, theoretical analysis and calculation on the basis of thermodynamics, crystallogy, so- lid physics,etc, have been applied to calculate the amount of atomic diffusion, which has further proved the testing results that joint Ag-Cu has strong bonding strength through the mechanism of atomic diffusion.展开更多
Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% ...Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.展开更多
The common Au nanostructures(nanospheres,nanorods and nanosheets)were prepared by the seed growth method to explore the cold welding phenomenon of these non-single crystal nanostructures at room temperature.Systematic...The common Au nanostructures(nanospheres,nanorods and nanosheets)were prepared by the seed growth method to explore the cold welding phenomenon of these non-single crystal nanostructures at room temperature.Systematic studies show that the concentration of surfactant cetyltrimethylammonium bromide(CTAB)and drying conditions are important factors to determine the evolution and final configuration of nanostructures during welding.The key factor of cold welding is the concentration of surfactant as low as 0.3 mm/L,and the welding should be carried out under the condition of slow evaporation and sufficient relaxation time,rather than rapid drying process.At the same time,the structural evolution during the welding process of gold rod head and tail is simulated by combining the electronic microscope characterization and density functional theory,which reveals that the stability of the welding nanostructure is better than that of the dispersed nanostructure.In the slow evaporation process of Au nanostructures with the same crystal structure,the low surfactant attached to the surface of the nanoparticles increases the attraction between the nanoparticles,which makes the nanoparticles close to each other adhere due to the interaction,and improves the physical properties of the intersection due to the diffusion,epitaxy and surface relaxation of the metal surface atoms.The results provide a research basis for the physical property analysis of nanostructures and the construction of defect devices.展开更多
基金Project (2010CB731704) supported by the National Basic Research Program of China
文摘The microstructure, phase composition and cold shut defect of thick titanium alloy electron beam welded joint were studied. The results showed that the microstructure of weld zone was composed of α′ phase; the heat affected zone was divided into fine-grained zone and coarse-grained zone, the microstructure of fine-grained zone was primary α phase ＋ β phase ＋ equiaxed α phase, and the microstructure of coarse-grained zone was primary α phase ＋ acicular α′ phase; the microstructure of base metal zone basically consisted of primary α phase, and a small amount of residual β phase sprinkled. The forming. reason of cold shut was analyzed, and the precaution of cold shut was proposed.
基金Project(9140C850205120C8501)supported by the Major Program of State Key Laboratory of Remanufacturing,China
文摘Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint was predicted by finite element （FE） method, while the structural morphology of distinctive zones was obtained through metallographic experiments. The highest principal stress made the symmetric face of the joint most sensitive to tensile cracks under service conditions. Whereas, the boundaries between the weld seam and the base plates were sensitive to cracks because the equivalent von Mises stress was the highest when the first interpass cooling was finished. The third weld pass and the inter-pass remelted zones exhibited the modest mechanical performances as a result of the coarse grain and coarse grain boundary, respectively. The most vulnerable zones were regarded to be the crossed parts between the zones identified by numerical and experimental methods.
文摘Aluminum and silver strips were cold welded by rolling and a bimetallic strip was produced. To create cold weld between A1 and Ag, mating surfaces were specially prepared and various rolling thickness reductions were applied. The minimum critical thickness reduction to begin cold weld was specified as 70% which equals 0.1630 critical rolling shape factors. The bimetallic strips were treated by diffusion annealing at 400 ~C and various annealing time. The A1/Ag interface of strips was observed by scanning electron microscope to investigate the formation of hard and brittle probable phases. The effect of anneal time on diffusion distance and phase transformation was also analysed by EDS analysis and line scan. A diffusion region along the interface in the Ag side was observed and its width increased with prolonging annealing time. Some 8 phases were detected close to the interface after anneal treating for 3 h and 8 phase was thicker and more continuous by increasing annealing time. The microhardness measurement showed that in spite of formation of 8 phase due to diffusion annealing, the interface hardness was reduced.
文摘The interfacial bonding of Ag-Cu (they are limited soluble) formed by the technology of cold pressure welding was discussed from the point of metallurgic view in this paper. Meanwhile, tensile test and microscopic test were adopted for studying the state of interfacial bonding, suggesting that the joint of Ag-Cu has not only strong welding joint but also atomic diffusion on the interface. For Ag-Cu, the interaction of dislocation caused by plastic deformation will cause the strain and the vibration of microconstructer defects, accompanied by emitting energy. The energy increases the atomic action and the amplitude of atomic vibration, and the result is that the atom can diffuse to several lattice parameters deep from interface to inner metals. Therefore, under the condition of chemical potential gradient, the special technique, cold pressure welding rather than basic requirements of diffusion should be taken into account. During the cold pressure welding, plastic deformation plays an important role for it causes the metals′ displacement, crystal defects, further activates the surface atoms. Finally, the fracture of atomic bonding leads to the atomic exchange and diffusion between the new metals′ surfaces.In other words the metals Ag,Cu can achieve solidate bonding by cold pressure welding accompanied by the atomic diffusion. Moreover, theoretical analysis and calculation on the basis of thermodynamics, crystallogy, so- lid physics,etc, have been applied to calculate the amount of atomic diffusion, which has further proved the testing results that joint Ag-Cu has strong bonding strength through the mechanism of atomic diffusion.
基金Project (51405392) supported by the National Natural Science Foundation of ChinaProject (2019T120954) supported by the China Postdoctoral Science Foundation+1 种基金Project (3102019MS0404) supported by Fundamental Research Funds for the Central Universities, ChinaProject (2018BSHQYXMZZ31) supported by the Postdoctoral Science Foundation of Shaanxi Province, China。
文摘Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.
基金supported by the National Natural Science Foundations of China (Nos. 11774171,11874220,21805137)the Open Funds of Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education (Nos. INMD-2019M02, INMD2020M03)+1 种基金the Scientific Foundation of Nanjing Institute of Technology(No. CKJB201708)the Fundamental Research Funds for the Central Universities(No.NS2017047) provided by Nanjing University of Aeronautics and Astronautics
文摘The common Au nanostructures(nanospheres,nanorods and nanosheets)were prepared by the seed growth method to explore the cold welding phenomenon of these non-single crystal nanostructures at room temperature.Systematic studies show that the concentration of surfactant cetyltrimethylammonium bromide(CTAB)and drying conditions are important factors to determine the evolution and final configuration of nanostructures during welding.The key factor of cold welding is the concentration of surfactant as low as 0.3 mm/L,and the welding should be carried out under the condition of slow evaporation and sufficient relaxation time,rather than rapid drying process.At the same time,the structural evolution during the welding process of gold rod head and tail is simulated by combining the electronic microscope characterization and density functional theory,which reveals that the stability of the welding nanostructure is better than that of the dispersed nanostructure.In the slow evaporation process of Au nanostructures with the same crystal structure,the low surfactant attached to the surface of the nanoparticles increases the attraction between the nanoparticles,which makes the nanoparticles close to each other adhere due to the interaction,and improves the physical properties of the intersection due to the diffusion,epitaxy and surface relaxation of the metal surface atoms.The results provide a research basis for the physical property analysis of nanostructures and the construction of defect devices.
