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1.
A mathematical model for flow simulation of full penetration laser beam welding of titanium alloy is presented. In this model, the heat source comprises a plane heat source on the top surface and a cylindrical heat source along the z-direction, which takes into account the plasma effect and the keyhole absorption. By solving the conservation equations of energy, momentum and mass, the temperature and flow fields are obtained. The momentum interpolation scheme with under-relaxation parameter is used to simplify the calculation algorithm and save the storage space of computer. The mushy region is introduced to provide a simple method to dispose of the pressure and velocity boundary conditions. Results calculated from the models are found to agree with the experimental results for the geometry profile of weld. The calculated results indicate the metal flow is the main reason for forming the typical “hourglass” cross-section profile. 相似文献
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Laser butt welding of titanium alloy to stainless steel was performed. The effect of laser-beam offsetting on microstructural characteristics and fracture behavior of the joint was investigated. It was found that when the laser beam is offset toward the stainless steel side, it results in a more durable joint. The intermetallic compounds have a uniform thickness along the interface and can be divided into two layers. One consists of FeTi + α-Ti, and other consists of FeTi + Fe2Ti + Ti5Fe17Cr5. When laser beam is offset by 0 mm and 0.3 mm toward the titanium alloy side, the joints fracture spontaneously after welding. Durable joining is achieved only when the laser beam is offset by 0.6 mm toward the titanium alloy. From the top to the bottom of the joint, the thickness of intermetallic compounds continuously decreases and the following interfacial structures are found: FeAl + α-Ti/Fe2Ti + Ti5Fe17Cr5, FeAl + α-Ti/FeTi + Fe2Ti + Ti5Fe17Cr5 and FeAl + α-Ti, in that order. The tensile strength of the joint is higher when the laser beam is offset toward the stainless steel than toward the titanium alloy, the highest observed value being 150 MPa. The fracture of the joint occurs along the interface between two adjacent intermetallic layers. 相似文献
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采用电子束对新型耐650 ℃使用的高温钛合金板材进行焊接,并进行1 000 ℃/1 h/AC+700 ℃/4 h/AC的退火处理,研究了接头的组织、硬度分布,母材和接头的拉伸性能和持久性能.结果表明,接头组织由α相、少量β相、以及大量细小的再结晶α相构成.接头中母材、热影响区和焊缝的显微硬度值比较均匀,介于440~490HV之间.室温条件下,母材和接头的抗拉强度均高于1 000 MPa,延伸率均介于7%~10%;650 ℃拉伸,母材抗拉强度达到了750 MPa,延伸率最高达20%;接头的抗拉强度在700 MPa以下,延伸率在10%~14%之间.接头与母材的持久断裂均是由孔洞聚集形成微裂纹,在力的作用下不断扩展,直至最终断裂.而接头中柱状晶的晶界促进了裂纹的扩展,所以母材的持久寿命和应变优于接头.根据结果分别得出了650 ℃下接头和母材应力与寿命的关系式. 相似文献
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Rattana Borrisutthekul Yukio Miyashita 《Science and Technology of Advanced Materials》2013,14(2):199-204
Joining technology of lightweight dissimilar metals between magnesium and aluminum alloys is essential for realizing hybrid structure cars and other engineering applications. In the present study, the normal center-line welding of lap joint was carried out by laser welding. It was found that the intermetallic layer formed near interface between two metals significantly degraded the joining strength. FEM heat transfer analysis was carried out to find out an available method to control penetration depth and width of molten metal, which contributes to control thickness of intermetallic compound layer. Based on the results of FEM analysis, the edge-line welding of lap joint was carried out, which could easily control the thickness of intermetallic layer and successfully obtained high joining strength. 相似文献
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Gap-free fibre laser welding of Zn-coated steel on Al alloy for light-weight automotive applications
As a result of new policies related to global warming announced by the European Union, avoiding unnecessary energy waste and reducing environmental pollution levels are becoming a major issue in the automotive industry. Accordingly, the lap welding of Zn-coated steels process, which is commonly used for producing car doors, has been gradually developed to lap welding of Zn-coated steel to light materials, such as Al alloy, Mg alloy and composite materials, in order to effectively reduce the vehicle weight. In certain part of car manufacture, organic glues are used to temporally join the Zn-coated steels and Al alloys before permanent welding takes place. The stability of such temporary joining by glues needs improving. Laser “stitching” or low strength welding could be considered as an alternative. However, challenges exist in joining Zn-coated steel on Al alloy by laser welding, due to significant differences of material properties between the two welding materials. Porosity, spatter and intermetallic brittle phases are readily produced in the weld. In this study, the effects of welding speed, laser power, number of the welding passes and type of shielding gas in gap-free welding of Zn-coated steel on Al alloy were investigated using a 1 kW single mode continuous wave fibre laser. Results show that a weld with higher shear strengths in the laser stitching application and less intermetallic phases could be obtained when nitrogen gas was used as the shielding gas. The corrosion resistance and the surface finish of the weld could be improved in double pass welding, especially when argon gas was used as the shielding gas. 相似文献
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This paper gives an account of research which has been carried out on electron‐beam welded specimens made of high‐Nb γ/α2‐titanium aluminides (in short: TiAl). The high niobium content of this alloy (5–8 %) has a positive effect on the strength and the creep resistance and also on the oxidation resistance. The standard welding parameters weld speed and beam current and also additional beam oscillation have been used for the determination of factors which will effect the solidification morphology and structural constitution since those, in return, exert influence on the high cracking susceptibility of the alloy. In order to reduce the critical cooling rate, preheating which has a positive effect on crack formation has, in addition, been applied. In a direct comparison of both alloys, micrographs and electron beam micro‐analyses of the developing weld structure and of the HAZ the effects of the beam parameters on both alloys have been established. 相似文献
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In this work, the current understanding and development of friction-stir welding and processing of Ti-6Al-4V alloy are briefly reviewed. The critical issues of these processes are addressed, including welding tool materials and design, tool wear, processing temperature, material flow, processing window and residual stresses. A particular emphasis is given to microstructural aspects and microstructure-properties relationship. Potential engineering applications are highlighted. 相似文献
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The effect of microstructural characteristics on fracture behaviour mechanism for electron beam welding of Ti-6Al-4V was investigated.
The results indicated that the welded microstructure composed of coarse needle α + β phases presenting disordered and multidirectional
short needle morphology to make fracture mechanism complex. The coarse grains in weld seam with microhardness 536 HV were
easy to be fractured in the region where welding heat input was ≥ 68.8 kJ/m. There exists flat curves of Ti, Al and V, Fe
concentration distribution fluctuation to cause microstructural amplitude-modulated decomposition to increase the joint ductility
and cleavage strength. The uneven distribution of the partial micropores located at the interior of the specimen acting as
crack initiation sites lead to non-linear branch propagating path. The α + β interlaced structure results in the fracture
location near α/β interface. The existence of stacking fault structure caused pile-up of dislocation to produce micropores
to be new fracture initiation sites. 相似文献
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Microstructural and mechanical characterization of laser beam welded AA6056 Al-alloy 总被引:3,自引:0,他引:3
Laser beam welding is considered to be a suitable joining process for high speed, low distortion, and high quality fabrication of aircraft structures manufactured from aluminum alloys, which are mainly preferred due to their favourable properties, such as high strength to weight ratio, ease of forming and high thermal and electrical conductivity. However, the laser beam welding of 6000 series aluminum alloys may exhibit a tendency to solidification cracking, and porosity may be a major problem unless appropriate welding parameters and filler metal are employed.In this study, the microstructural aspects and mechanical properties of laser beam welded new generation aluminum alloy, namely 6056, developed especially for aircraft structures, are investigated. A continuous wave CO2 laser using AlSi12 filler wire was employed. A detailed microstructural examination of the weld region was carried out by Scanning Electron Microscopy (SEM). Standard tensile and microflat tensile specimens extracted from the welded plates were tested at room temperature for the determination of general and local mechanical properties of the welded joints. Extensive microhardness measurements were also conducted. Crack growth mechanisms of the joints produced were also determined by conducting fatigue tests under various stress ratios (i.e., 0.1 ≤ R ≤ 0.7). 相似文献
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The Nd:YAG laser welding was used to join the binary NiTi alloy wires with different compositions(Ti-50.0 at.%Ni and Ti-50.9 at.%Ni) which had the same diameter of 1 mm. The wires were welded with different parameters, including impulse width and welding current. The aim was to assess the influence of the laser-welding process on the microstructure and mechanical properties of the welded joint of binary NiTi wires. The optical microscopy (OM) and the metallographic microscopy (MM) were used to analyze the microstructure of the welded joints. The tensile test and the differential scanning calorimetry (DSC) were carried out to examine the ultimate tensile strength and the reverse martensitic transformation temperatures of the welded joints. It was found that the welding current and the impulse width had great influence on the quality of the welded joints, an optimal parameter combination would remove the pores and micro-cracks appeared in the fusion zone, and result in good mechanical properties such as higher fracture strength and elongation. The laser welding had a few effect on the reverse martensitic transformation temperatures of the welded joints. 相似文献
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Mohandas Srinivas & Kutumbarao 《Fatigue & Fracture of Engineering Materials & Structures》2000,23(1):33-38
The effects of a post-weld heat treatment on the fracture toughness and fatigue crack growth behaviour of electron beam welds of an α + β titanium alloy, Ti–6.5Al–1.9Zr–0.25Si have been studied. Welds in the stress-relieved condition exhibited poor fracture toughness due to poor energy absorbing capacity of the thin α and α' phases. Post-weld heat treatment which resulted in the decomposition of α' to α + β and the coarsening of intragranular and intergranular α resulted in improved toughness. This improvement in the toughness is related to improved ductility leading to crack blunting, crack path deviation at the thick intragranular and intergranular α phase. Fatigue crack growth resistance of welds was superior to the base metal in the α + β heat-treated condition. The superior crack growth resistance of the welds is due to the acicular α microstructure which results in a tortuous crack path and possible crack closure arising from crack path tortuosity. 相似文献
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Comparative study of fatigue and fracture in friction stir and electron beam welds of 24 mm thick titanium alloy Ti‐6Al‐4 V
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Paul D. Edwards M. Ramulu 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(10):1226-1240
In this study, friction stir welding of Ti‐6Al‐4 V was demonstrated in 24 mm thickness material. The microstructure and mechanical properties, fatigue, fracture toughness and crack growth of these thick section friction stir welds were evaluated and compared with electron beam welds produced in the same thickness material. It was found that the friction stir welds possessed a relatively coarse lamellar alpha transformed beta microstructure because of slow cooling from above the transus temperature of the material. The electron beam welds had a fine acicular alpha structure as a result of rapid solidification. The friction stir welds possessed better ductility, fatigue life, fracture toughness and crack growth resistance than the base meal or electron beam welds. Thus, even though friction stir welding is a relatively new process, the performance benefits it offers for the fabrication of heavy gage primary structure make it a more attractive option than the more well‐established electron beam welding method. 相似文献
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In the aircraft industry double-sided laser beam welding of skin–stringer joints is an approved method for producing defect-free welds. But due to limited accessibility – as for the welding of skin–clip joints – the applicability of this method is limited. Therefore single-sided laser beam welding of T-joints becomes necessary. This also implies a reduction of the manufacturing effort. However, the main obstacle for the use of single-sided welding of T-joints is the occurrence of weld defects. An additional complexity represents the combination of dissimilar and hard-to-weld aluminium alloys – like Al–Cu and Al–Zn alloys. These alloys offer a high strength-to-density ratio, but are also associated with distinct weldability problems especially for fusion welding techniques like laser beam welding. The present study demonstrates how to overcome the weldability problems during single-sided laser beam welding of a dissimilar T-joint made of AA2024 and AA7050. For this purpose a high-power fibre laser with a large beam diameter is used. Important welding parameters are identified and adjusted for achieving defect-free welds. The obtained joints are compared to double-sided welded joints made of typical aircraft aluminium alloys. In this regard single-sided welded joints showed the expected differing weld seam appearance, but comparable mechanical properties. 相似文献
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Dissimilar Mg alloy and Q235 steel lap joints are produced by Laser‐ tungsten inert gas (TIG) hybrid welding with Ni as an interlayer. Fe and Ni are joined together in the form of solid solution, while Mg alloy and Ni foil are joined together by intermetallic compound Mg2Ni. During tensile testing, the joints fail at the interface between Ni foil and Mg alloy. The shear strength of the Mg/Steel joints with Ni as interlayer is 170 MPa, which is higher than that without interlayer 120MPa. 相似文献
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Reasons for superior mechanical and corrosion properties of 2219 aluminum alloy electron beam welds 总被引:1,自引:0,他引:1
S.R. Koteswara Rao G. Madhusudhan Reddy K. Srinivasa Rao M. Kamaraj K. Prasad Rao 《Materials Characterization》2005,55(4-5):345-354
Electron beam welds of aluminum alloy 2219 offer much higher strength compared to gas tungsten arc welds of the same alloy and the reasons for this have not been fully explored. In this study both types of welds were made and mechanical properties were evaluated by tensile testing and pitting corrosion resistance by potentio dynamic polarization tests. It is shown that electron beam welds exhibit superior mechanical and corrosion properties. The weld metals have been characterized by scanning electron microscopy; transmission electron microscopy and electron probe micro analysis. Presence of partially disintegrated precipitates in the weld metal, finer micro porosity and uniform distribution of copper in the matrix were found to be the reasons for superior properties of electron beam welds apart from the fine equiaxed grain structure. Transmission electron micrographs of the heat affected zones revealed the precipitate disintegration and over aging in gas tungsten arc welds. 相似文献
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The influence of focusing thermal effect upon the weld shape, microstructure and alloying elements distribution in the welded joints during vacuum electron beam welding on AZ91D magnesium alloy was studied. The results show that the focus state affects the offset of DOF, and further significantly affects the actual welding heat input in the process of vacuum electron beam welding. The sharp focusing state is characterized with higher welding energy density, but the welding energy density of defocusing state is lower. Therefore, the welding process with sharp focusing state and smaller calculation welding heat input can obtain the same weld penetration as the welding process is the conditions of defocusing state and larger calculation welding heat input. And the welding process of sharp focusing state and smaller calculation welding heat input can induce more strongly burning loss of Mg element than the conditions of defocusing state and larger calculation welding heat input. Then, which will affect the distribution of alloy elements in weld seam. 相似文献