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RISS 인기검색어
- 검색키워드
- 저자 : Xiyuan Hu (검색결과 6 건)
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Atomistic simulations for the non-equilibrium surface premelting and melting of Nb(1 1 0) plane
Xiyuan Yang,Wangyu Hu,Zhi Zhang 한국물리학회 2010 Current Applied Physics Vol.10 No.2
In the present paper molecular dynamics (MD) simulations have been preformed to investigate the surface melting process and microscopic mechanism of Nb(1 1 0) plane in the atomic scale with a modified analytic embedded atom method (MAEAM). On the basis of the MD relaxation dependence of averaged internal energy and layer structure factor at given temperatures, the melting point of the sample has been estimated to be 2510 K. Then by the above results the Nb(1 1 0) plane melting process has been approximately divided into two stages: first the layer-by-layer premelting phase in the surface region and then a simultaneous abrupt melting transition for the inner layers. According to the variation of the averaged internal energy of the inner atomic layer, the melting latent heat has been calculated and the result is in good agreement with the experimental value. The simulated snapshots of atomic configuration for Nb(1 1 0) plane have indicated that the dynamically microscopic mechanism of melting nucleation during the melting transition.
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Porosity in fiber laser formation of 5A06 aluminum alloy
Yangchun Yu,Chunming Wang,Xiyuan Hu,Jun Wang,Shengfu Yu 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.5
The mechanism of porosity formation and its suppression methods in laser formation of aluminum alloy have been studied using a 4kW fiber laser to weld 5A06 aluminum alloy with SAl-Mg5 filler. It was found that the porosity formation is closely related to the stability of the keyhole and fluctuation of the molten pool in the laser welding aluminum alloy. The filling wire increased the instability of the keyhole and weld pool, thus further increasing the amount of gas cavities in the joint. Prefabrication of a suitable gap for the butt joint can provide a natural passage for the flow of the liquid metal, which can weaken, and even completely eliminate the disturbance of the filling wire on the formation of keyhole. The gap can also provide a passage for the escape of the bubble. Thus, this method can greatly decrease the sheet’s susceptibility to porosity. Moreover, for a thin sheet, if the power of the laser is sufficient to form a keyhole with stable penetration through the weld sheet, a weld bead without porosity can also be obtained because closing the keyhole is almost impossible.
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Interaction between laser-induced plasma/vapor and arc plasma during fiber laser-MIG hybrid welding
Jun Wang,Chunming Wang,Xuanxuan Meng,Xiyuan Hu,Yangchun Yu,Shengfu Yu 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.6
Hybrid plasma is an important physical phenomenon in fiber laser-MIG hybrid welding. It greatly affects the stability of the process,the quality of the weld, and the efficiency of energy coupling. In this paper, clear and direct proofs of these characteristics are presented through high-speed video images. Spectroscopic analysis is used to describe the characterization of hybrid plasma. The hybrid plasma forms a curved channel between the welding wire and the keyhole during the fiber laser-MIG hybrid welding process. The curved channel is composed of two parts. The laser-induced plasma/vapor expands due to the combined effect of the laser and the MIG arc, forming an ionization duct, which is one part of the curved channel. The resistance of the duct is smaller than that of other locations because of the rise in electrical conductivity. Consequently, the electrical arc is guided through the duct to the surface of the material, which is the other part of the curved channel. The spectral intensities of metal elements in laser-MIG hybrid welding are much stronger than those in MIGonly welding, whereas the spectral intensities of shielding gas element in laser-MIG hybrid welding are much weaker.
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Morphology, microstructure, and mechanical properties of laser-welded joints in GH909 alloy
Chunming Wang,Yuanzheng Cai,Chongjing Hu,Xiong Zhang,Fei Yan,Xiyuan Hu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5
The experimental laser welding of GH909 alloy was conducted in this study. The morphology, microstructure, and mechanical properties of laser-welded joints were analyzed by scanning electron microscopy, energy diffraction spectroscopy, and other techniques. Results revealed that the microstructure of the welded joints mainly consisted of tiny cellular structures, dendritic structures, and equiaxed crystals. Pores appeared in the interdendritic regions because of the insufficient local feeding of molten metal during solidification. Nb segregation in the heat-affected zone caused liquation cracking, whereas C segregation further induced the formation of carbide precipitates along the grain boundaries during the welding thermal cycle. The instability of the keyhole significantly promoted the escape of the metal vapor/plasma from the hole; as a result, porosity defects formed in the weld. The average tensile strength of the test joints was 756 MPa, which is 93.1 % of that of the base metal. The average microhardness of the weld zone (250 HV) was higher than that of the GH909 alloy substrate (208 HV), peaking at 267 HV. Microcracks appeared along the grain boundaries, proving that the grain boundaries were the weakest areas in the joint.
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Study on softening behavior of laser welded joint in GH909 alloy
Fei Yan,Tao Zhan,Sang Liu,Zhengwu Zhu,Chunming Wang,Xiyuan Hu 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11
Laser beam welding was conducted on GH909 alloy in a solution treatment and aging conditions. The microstructure, mechanical properties, and softening behavior of welded joints were carefully studied using scanning electron microscopy, energy diffraction spectroscopy, and other techniques. Results indicated that γ′-Ni 3 (TiAl)-precipitated phases were produced inside the matrix, and the presence of Laves at grain boundaries restricted grain growth. A sharp reduction in γ′-precipitated phases evidently weakened the average tensile strength and microhardness of the welded joints. Moreover, fractures occurred in the weld zone. Microcracks in the fracture of the joint mainly depended on the competition result between thermal stress and cohesion forces among the grains.
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Investigation of melting dynamics of filler wire during wire feed laser welding
Yangchun Yu,Wei Huang,Guozhen Wang,Jun Wang,Xuanxuan Meng,Chunming Wang,Fei Yan,Xiyuan Hu,Shengfu Yu 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.4
In order to investigate the mechanism of stability for the wire feed laser welding process, systematic experiments are carried out in this study for 5A06 aluminum alloy. By using high speed camera, the melting dynamics of filler wires with different feed positions and feed rates are studied. The results indicate that these two factors mainly influence the characteristics of the filler wire melting dynamics and determine the stability of the welding process. The melting dynamics of filler wire can be generally characterized by three different forms: explosion, big droplet and molten metal bridge. When the filler wire melts and transits to the molten pool in the forms of explosion or big droplet, the stability of the welding process is strongly disturbed, resulting in an undesirable weld quality. In contrast, when it is in molten metal bridge form, the welding process is more stable and a uniform weld bead is achieved.
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