Electron Beam Welding Joints Research Articles

Microstructure and magnesium burning loss behavior of AA6061 electron beam welding joints

Full penetration butt welding with different parameters was performed on 4mm thick AA6061 plates. The microstructural characteristics, element burning loss behavior and their effects on the mechanical properties of the weld beams were studied. It revealed that the weld porosity could be effectively controlled with a lower welding velocity and the crystal enlargement is rather obvious near the weld upper surface. The secondary-precipitated phase AlFeSi was observed at the crystal boundaries, whereas the strengthening phase Mg2Si within the welds is undetectable by SEM. The magnesium burning loss behavior of the welds embodies in two aspects: the decrease in magnesium content compared to the original alloy and the uneven distribution of magnesium with a decrease tendency as close to the weld surface and a symmetric growth as further away from the seam center line. The welded joints with a higher burning loss degree of magnesium are performed at a lower Vickers hardness, tensile strength, plasticity and toughness. The characteristic isotherm and convection within the molten pool during EBW were considered as the key factors that dominated the microstructure and magnesium distribution.

Microstructure and Mechanical Properties of Powder Metallurgy Ti-22Al-24Nb-0.5Mo Alloys Joints with Electron Beam Welding

In this work, a Ti2AlNb based intermetallic alloy with the composition of Ti–22Al–24Nb–0.5Mo (at. %) pre-alloyed powder was firstly produced by gas atomization, and then fully dense powder metallurgy (PM) Ti2AlNb alloy was prepared by a hot isostatic pressing (HIPing) procedure. The HIPed alloy shows uniform microstructure with low number of porosities. In order to broaden the application field of PM Ti2AlNb alloys, electron beam welding (EBW) was proposed to join the intermetallics. The joint quality, microstructure and microhardness of PM Ti2AlNb alloy processed by EBW were characterized, and the results showed that the both base alloy and EBW joints have high metallurgy quality.

Tensile mechanical performance of electron-beam welded joints from aluminum alloy (Al-Mg-Si) 6156

The mechanical behavior of both, reference and electron beam welded aluminum alloy 6156 specimens was experimentally investigated. Sheets of AA6156 were artificially aged before and after the welding process and tensile specimens were machined from the welded sheets according to the ASTM E8 standard. The specimens were artificially aged at 170°C for different times that corresponded to all precipitation-hardening conditions, namely under-ageing (UA), peak-ageing (PA) and over-ageing (OA). The results showed that the effect of welding without any heat treatment (condition T4) decreases by, about 100 MPa, the yield stress and the yield strength, while the remaining elongation at fracture hardly exceeds 4 %. It was also shown that artificial ageing before welding increases the tensile ductility (almost 50 % joint efficiency in deformation) while the artificial ageing post to welding significantly increases the strength properties (more than 75 % joint efficiency in strength).

Plastic deformation behavior and bonding strength of an EBW joint between 9Cr-ODS and JLF-1 estimated by symmetric four-point bend tests combined with FEM analysis

The joint between 9Cr-ODS and JLF-1 made by electron beam welding (EBW) fractured at the JLF-1 base metal (BM) during uniaxial tensile tests. Thus, the bonding strength of the joint was not determined and was estimated as more than the ultimate tensile strength of the BM in this case. Symmetric four-point bend tests which concentrate the stress inside the inner span including the weld metal (WM) were carried out at room temperature (RT) and 550°C to investigate how the bonding strength is more than the ultimate tensile strength of the BM. The normal stress at the center of the weld bead can be calculated with elastic theory up to only 0.25% in strain, though the joint showed more than 10% in strain due to plastic deformation. Thus, finite element method (FEM) was utilized to simulate the plastic deformation behavior of the joint during bend tests. According to the fitting of the FEM output, such as load and displacement of the upper jig contacting the specimens, to the experimental results, the bonding strength of the joint at RT and 550°C were estimated as 854MPa and 505MPa, respectively.

Qualification of electron-beam welded joints between copper and stainless steel for cryogenic application

Joints between copper and stainless steel are commonly applied in cryogenic systems. A relatively new and increasingly important method to combine these materials is electron-beam (EB) welding. Typically, welds in cryogenic applications need to withstand a temperature range from 300K down to 4K, and pressures of several MPa. However, few data are available for classifying EB welds between OFHC copper and 316L stainless steel. A broad test program was conducted in order to qualify this kind of weld. The experiments started with the measurement of the hardness in the weld area. To verify the leak-tightness of the joints, integral helium leak tests at operating pressures of 16 MPa were carried out at room- and at liquid nitrogen temperature. The tests were followed by destructive tensile tests at room temperature, at liquid nitrogen and at liquid helium temperatures, yielding information on the yield strength and the ultimate tensile strength of the welds at these temperatures. Moreover, nondestructive tensile tests up to the yield strength, i.e. the range in which the weld can be stressed during operation, were performed. Also, the behavior of the weld upon temperature fluctuations between room- and liquid nitrogen temperature was tested. The results of the qualification indicate that EB welded joints between OFHC copper and 316L stainless steel are reliable and present an interesting alternative to other technologies such as vacuum brazing or friction welding.

Localized microstructural characterization of a dissimilar metal electron beam weld joint from an aerospace component

Hydrogen induced cold cracking (HICC) and hydrogen embrittlement (HE) are influenced by the microstructural evolution, residual plastic strain (i.e. local misorientation), recrystallization of grains and the resultant grain boundary characteristic distribution (GBCD) brought about by welding processes. HICC and HE are known to cause failures in aerospace components and it is vitally important to quantify the microstructural evolution, degree of residual plastic strain and determine the GBCD across dissimilar weld joints in order to assess the susceptibility of the weld joint to these phenomena. In this investigation a full a microstructural characterization study was carried out at various locations within and around a dissimilar weld joint of pulse-plated nickel (PP-Ni) and Inconel 718 (IN718), taken from an aerospace component. Areas examined included the base metals, weld fusion zone and heat affected zones on both sides of the weld joint, formed via electron beam welding. Scanning electron microscopy (SEM) in combination with electron backscatter diffraction (EBSD) was employed to measure the residual plastic strain, grain structure, grain size distribution, crystal orientation distribution, grain boundary misorientation distribution and GBCD of the dissimilar metal weld joint. Finally a metallurgical examination was carried out using SEM on the IN718 HAZ in order to investigate the secondary phase precipitation arising from the welding process. The results shows large variety of GBCD, crystallographic orientation distribution, local plastic strain distribution and grain size, shape and structure distribution across dissimilar weld joint. And these localized microstructural characterized data sets need to be carefully transferred using data-driven approach in order to develop predictive multiscale material modelling for hydrogen induced cracking and hydrogen embrittlement.

Effect of Non-Uniform Deformation on Low Cycle Fatigue Properties of Electron Beam Weld Joint of F82H Steel

To improve the fatigue properties evaluation of the joint region of the fusion reactor blanket, the effect of the non-uniform distribution of the microstructure and strength on the fatigue properties of the electron beam weld joint of the F82H steel was investigated by the fatigue test and the numerical simulation of the deformation under the test. The fatigue life of the joint was approximately 10–20 % of that of the base metal. The fracture under the fatigue test occurred around the over-tempered heat affected zone (the region with the lowest hardness). One of the reasons of the shorter fatigue life of the joint could be the higher crack growth rate induced by the peak strain around the over-tempered heat affected zone due to the non-uniform deformation.

A comparative study on electron beam welding and rigid restraint thermal self-compressing bonding for Ti6Al4V alloy

This study focuses on the influence of joining method difference on the joint microstructure and properties. Unlike vacuum electron beam welding (EBW) utilizing electron beam as fusion heat source, rigid restraint thermal self-compressing bonding (TSCB), a new solid-state bonding method proposed by authors, employs vacuum electron beam as the non-melt heat source to bond materials in this work. Meanwhile, a comparative study on the microstructure and mechanical properties of EBW joint and rigid restraint TSCB joint was conducted to investigate the effect of this difference on joint microstructure and properties. Results show that compared with EBW joints, the rigid restraint TSCB joints as solid-state joints are homogeneous in terms of microstructure and microhardness profile. Strength of both joints are comparable with that of base metal, but the elongation of the rigid restraint TSCB joint is more close to that of base metal. Rigid restraint TSCB joint has better combination of strength and ductility.

Effects of Metal Types on Residual Stress in Electron-Beam Welding Joints with Sheet Metals

Effects of Metal Types on Residual Stress in Electron-Beam Welding Joints with Sheet Metals

Effects of the Heterogeneity in the Electron Beam Welded Joint on Mechanical Properties of Ti6Al4V Alloy

The aim of this investigation was to evaluate the effect of microstructure heterogeneity on the tensile and low cycle fatigue properties of electron beam welded (EBW) Ti6Al4V sheets. To achieve this goal, the tensile and low cycle fatigue property in the EBW joints and base metal (BM) specimens is compared. During the tensile testing, digital image correlation technology was used to measure the plastic strain field evolution within the specimens. The experimental results showed that the tensile ductility and low cycle fatigue strength of EBW joints are lower than that of BM specimens, mainly because of the effect of microstructure heterogeneity of the welded joint. Moreover, the EBW joints exhibit the cyclic hardening behavior during low fatigue process, while BM specimens exhibit the cyclic softening behavior. Compared with the BM specimens with uniform microstructure, the heterogeneity of microstructure in the EBW joint is found to decrease the mechanical properties of welded joint.

Relationship between the Textures and the Elastic Moduli of Electron Beam Welded Joint in Ti-6Al-4V Titanium Alloy

The microstructure, texture and elastic modulus of electron beam welding joint in Ti-6Al-4V titanium alloy were investigated by transmission electron microscopy, X-ray diffraction, electron back scattered diffraction and nanoindentation techniques. The α phase was in the majority, and a {0001} <-2110> texture of α phase was observed in the base material. A very weak {11-23} <-1-122> texture of α phase was in the fuse zone. Most of the α grain boundaries in the fuse zone were high-angle boundaries by electron backscattered diffraction, and it also confirmed that the orientations of α phase had a nearly random distribution in the fuse zone. The maximum average elastic modulus value measured by the nanoindentation techniques was in the base material due to the effect of the {0001} <-2110> texture. The average elastic moduli of three different zones in the joint were 134.8±3.5Gpa, 125.5±5.8Gpa and 123.0±4.7Gpa, respectively.

Research on fatigue behavior of electron beam welding joint of 06Cr19Ni10 austenitic stainless steel sheet

06Cr19Ni10 austenitic stainless steel sheet square butt joints without filler metal addition were fabricated using EBW (electron beam welding) processes. Fatigue properties, tensile properties and microstructure of the welded joints were studied. It was found that the yield strength, tensile strength, elongation and Vickers hardness of EBW joint can reach the level of base material performance. Fusion zones consist of coarse columnar dendritic grains, which are perpendicular to the weld pool boundary. The hardness of heat affected zone is lower than weld centreline. The reason is that the grain of heat affected zone under the action of electron beam heat source happened recovery and recrystallization. The present work suggests that S–N curve slope ofwelding joint should be revised to m=10 under the condition of high stress levels, and S–N curve slope is still m=3.0 under the condition of low stress levels. Fatigue cracks did not extend along the minimum thickness of the section. On the contrary, fatigue cracks extended along the maximum height of the section.

Ti–6Al–4V welded joints via electron beam welding: Microstructure, fatigue properties, and fracture behavior

The effect of microstructural characteristics on the fatigue properties of electron beam-welded joints of forged Ti–6Al–4V and its fracture behavior were investigated. Tensile tests and fatigue tests were conducted at room temperature in air atmosphere. The test data were analyzed in relation to microstructure, high-cycle fatigue properties, low-cycle fatigue properties, and fatigue crack propagation properties. The high-cycle fatigue test results indicated that the fatigue strength of the joint welded via electron beam welding was higher than that of the base metal because the former had a high yield strength and all high-cycle fatigue specimens were fractured in the base metal. Although the joint specimens had a lower low-cycle fatigue life than the base metal, they mainly ruptured at the fusion zone of the joint specimen and their crack initiation mechanism is load-dependent. The fatigue crack propagation test results show that the joint had a slower crack propagation rate than the base metal, which can be attributed to the larger grain in the fusion zone.

Fatigue crack growth of titanium alloy joints by electron beam welding

Electron beam welding (EBW) has been widely used in the manufacture of titanium alloy welded blisk for aircraft engines. Based on fatigue crack growth tests on titanium alloy electron beam welding (EBW) joints, mechanism of fracture was investigated under scanning electron microscope (SEM). The results show that fatigue crack growth rate increases as the experimental load increases under the same stress ratio and stress intensity factor range. At the beginning of crack growth, the extension mechanism of fatigue crack is the typical mechanism of cleavage fracture. In the steady extention stage, crack extends along the weld seam firstly. Then, crack growth direction changes to extend along the base metal. The extension mechanism of fatigue crack in the weld seam is the main mechanism of cleavage fracture and the extension mechanism of fatigue crack in the base metal is the main extension mechanism of fatigue band. In the instantaneous fracture stage, the extension mechanism of fatigue crack is the typical dimple-type static fracture mechanism. Crack growth was simulated by conventional finite element method and extended finite element method.

Effect of post-weld heat treatment on the mechanical properties of electron beam welded joints for CLAM steel

In this paper the microstructure and mechanical properties of electron beam weld (EBW) joints for China low activation martensitic (CLAM) steel, which underwent a series of different post weld heat treatments (PWHTs) were studied. The aim of the study was to identify suitable PWHTs that give a good balance between strength and toughness of the EBW joints. The microstructural analyses were performed by means of optical microscope (OM) and scanning electron microscope (SEM). The mechanical properties were determined via tensile tests and Charpy impact tests. The results showed that the tensile strength of the as-weld joint (i.e. without any PWHT) were close to that of the base metal, but the impact toughness was only 13% of that of the base metal due to the existence of a delta-ferrite microstructure. To achieve a significant improvement in toughness a PWHT needs to be performed. If a one-step PWHT is applied tempering at 760°C for 2h gives EBW joints with high strength at a still acceptable toughness level. If a two-step PWHT is applied, a process involving quenching at 980°C for 0.5h followed by tempering at 740°C or 760°C for 2h gives EBW joints with high strength and toughness properties. Whenever possible a two-step PWHT should be applied in favor of a one-step process, because of higher resulting strength and toughness properties.

Effect of Electron Beam Welding on Microstructure and Mechanical Properties of Spray-Deposited Al-Zn-Mg-Cu Alloy

In this study, Al-8.6Zn-2.6Mg-2.2Cu (wt,%) alloy was synthesized by the spray atomization and deposition technique. Electron beam welding (EBW) joint in the spray-deposited Al-8.6Zn-2.6Mg-2.2Cu alloy is composed of fusion zone, heat affected zone and base metal region. The microstructure of the fusion zone has been found to be very fine equiaxed grains, and the microstructure of the heat affected zone is mainly composed of α-Al and Al/MgZn2 eutectic microstructure. Extensive microhardness measurements were conducted in the weld regions of the nuggets exhibited a hardness loss in the fusion zone due to the loss of strengthening phases. Tensile properties test results indicated that tensile strength of these welds approached 82.3~85.3% of the base metal. The analysis of fracture surface has confirmed that the specimen fractured within the weld region during tensile test.

Study on electron beam weld joints between pure vanadium and SUS316L stainless steel

The mechanical and metallographical properties of the electron beam weld joints between pure vanadium (V) and SUS316L austenitic stainless steel and the effect of post-welding heat treatment (PWHT) at 873 and 1273K for 1h on these properties were investigated. The electron beam was shifted by 0.2mm (EB02S), 0.4mm (EB04S), and 0.6mm (EB06S) on the SUS316L side. No significant defects (e.g., pores, macro-cracks, or micro-cracks) were observed in the as-welded EB02S and EB04S joints, whereas a non-welded region was formed in the as-welded EB06S joint. Much higher hardness was observed in the weld metal (WM) of the as-welded EB02S and EB04S joints than in the base metals (BMs), which might be attributed to solution hardening. A significant increment in the hardness of the WM of EB02S joint occurred due to the PWHT at 873 and 1273K, which might be attributed to solution hardening and formation of Ni2V3 and NiV3 precipitates. Almost no change in the hardness due to the PWHT at 873 and 1273K occurred in the WM of the EB04S joint. The interlayer was formed at the edge of the WM of the V side only in the post-welding heat-treated EB04S joint. The interlayer showed much higher hardness than the BMs and WM, which might be attributable to solution hardening, formation of σ phase of the Fe–V system, and formation of Ni2V3 and NiV3 precipitates.

Microstructure of Al-Li Alloy Electron Beam Welding Joint after Post-Weld Heat Treatment

Heat treatment was carried out to the 1420 Al-Li alloy electron beam welding (EBW) joints after welding, and the microstructures of welded joints are analyzed systematically before and after post-weld heat treatment (PWHT). The observation of joint microstructure demonstrates that the grain morphology of weldment changes from equiaxed dendrites in as-welded (AW) condition into equiaxed grains after PWHT, and that the fine strengthening phases precipitate within the grain. The XRD analysis of phase constituent and TEM observation of weldment indicate that the main strengthening phases in 1420 Al-Li alloy weldment are spheroidal δ′(Al3Li), β′(Al3Zr) and rod-like T(Al2MgLi) after PWHT. Furthermore, the δ′ phase precipitate free zone (PFZ) is found along the grain boundary. The scanning observation of joint fracture shows that Al-Li alloy EBW joint presents the characteristic of transgranular ductile fracture in AW condition. After PWHT, the Al-Li alloy welded joint presents the pattern of intergranular fracture. The variation of fracture mode is related to dispersed precipitation of δ′ phase and the formation of PFZ at the grain boundary in weldment after heat treatment.

Influences Of Welding Processes And Post- Weld Ageing Treatment On Mechanical And Metallurgical Properties Of Aa2219 Aluminium Alloy Joints

AA2219 aluminium alloy joints without filler metal addition were fabricated using gas tungsten arc welding (GTAW), electron beam welding (EBW) and friction stir welding (FSW) processes. The fabricated joints were post weld aged at 175 °C for 12 h. Microstructure analysis was carried out using optical and electron microscopes. It was found that the FSW joints were exhibiting superior tensile and fatigue properties compared to EBW and GTAW joints. Post-weld ageing treatment was found to be beneficial to enhance the tensile and fatigue properties of the welded joints, irrespective of welding processes. Post weld aged FSW joints showed the highest joint efficiency of 80 % and hence this process can be preferred over other welding processes to fabricate components and structures using AA2219 aluminium alloys.

薄板の電子ビーム溶接継手における残留応力・変形特性

薄板の電子ビーム溶接継手における残留応力・変形特性