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Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy
摘要： Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.
关键词： Cooling rate,Laser welding,Grain refinement,Niobium alloy,Mechanical properties,Nb-1% Zr-0.1% C
更新于2025-09-23 15:19:57
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Finite-element inverse analysis of residual stress for laser welding based on a contour method
摘要： The thermal effect of laser welding degrades the local material properties, and this inevitably leads to thermal deformation and thermal residual stress in welded joints. In this study, the residual stress distribution of laser-welded Al–Li alloy parts was measured by a combination of the contour method and finite-element simulation. First, the contour deformation of the cutting surfaces of welded parts resulting from the release of residual stress was measured by a coordinator. Then, the reverse contour deformation was applied to the finite-element model as the displacement boundary condition to invert the full-field residual stress of the cutting surface. Furthermore, a thermal/structural sequential coupling analysis method was used to establish a complete three-dimensional finite-element model of a laser-welded plate and calculate the residual stress field, taking the actual weld morphology as the characteristic parameter of the heat source, using the improved conical heat source model of laser welding. The result is consistent with the results of the contour method.
关键词： Laser welding,Residual stress,Contour method,Thermal/structural finite-element analysis,Improved conical heat source model
更新于2025-09-23 15:19:57
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Correlation between plume fluctuation and keyhole dynamics during fiber laser keyhole welding
摘要： In order to reveal the fluctuation mechanism of the plume induced during fiber laser keyhole welding, dynamic behaviors of both the plume and the keyhole were simultaneously observed by using the multiple-imaging method. The results show that the fluctuation period of the plume was the same as that of the laser-induced vapor moving down on the keyhole front wall (KFW). The tilt angle of the plume was the largest when the laser-induced vapor was close to the orifice. As the laser-induced vapor moved toward the bottom of the KFW, the tilt angle of the plume decreased gradually. The correlation between the plume fluctuation and the dynamics of the laser-induced vapor on the KFW was not affected by parameters such as welding speed, laser power, and focal length. Further analysis shows that the periodic drilling behavior of the laser spot on the KFW is the main reason for the periodic fluctuation of the plume.
关键词： KFW,plume,fiber laser welding,laser-induced vapor,fluctuation
更新于2025-09-23 15:19:57
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Femtosecond laser-induced non-thermal welding for a single Cu nanowire glucose sensor
摘要： Copper nanowires (CuNWs) are a key building block to facilitate carrier conduction across a broad range of nanodevices. For integration into nanoscale devices, manipulation and welding of these nanowires need to be overcome. Based on high energy density laser processing investigation, we report on innovative welding of single CuNWs to a silver film using a tightly focused laser beam combined with manipulation of CuNWs through the dielectrophoresis (DEP) method. Two types of lasers, femtosecond (FS) and continuous-wave (CW), were employed to analyze, improve, and control Cu-NW melting characteristics under high energy density irradiation. The FS laser welding of CuNWs resulted in a metallic joint with a low contact resistance suitable for functional electronic nanodevices. Computational simulations using the 1-D heat diffusion equation and finite difference method (FDM) were performed to gain an insight into metal–laser interactions for high performance welded contact development. Simulation studies on lasers established contrasting melting behavior of metal under laser irradiation. The device feasibility of CuNW based welded contacts was evaluated in terms of the electrical performance of a glucose sensor. It was possible to sense glucose concentration down to 10?6 M, demonstrating a path towards integration of CuNWs into wearable, flexible nanoelectronic devices.
关键词： glucose sensor,femtosecond laser,Copper nanowires,laser welding,dielectrophoresis,nanoelectronics,continuous-wave laser
更新于2025-09-23 15:19:57
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Vapor plume and melted zone behavior during dissimilar laser welding of titanium to aluminum alloy
摘要： The present study deals with continuous Yb:YAG laser welding of pure titanium to aluminum alloy A5754 performed with different beam offsets to the joint line. Spectroscopic and morphological characterization of vapor plume exiting the keyhole was combined with post-mortem observation and energy-dispersive X-ray spectroscopy (EDX) analysis of the welds. The laser beam centered on the joint line resulted in periodic transversal inclination of a vapor jet on the aluminum side associated with a local increase of melt width and an intense spatter formation. Such behavior can be attributed to the instability of the keyhole wall from the aluminum side. The beam offset on the titanium side led to the stabilization of vapor plume, the attenuation of spattering, and a minimal mixing between the two liquid metals. On the contrary, the beam offset on the aluminum side produced a violent formation of spatters and a highly unstable, diffuse vapor jet. In this case, the liquid metals underwent a violent mixing that was progressively reduced along with the decrease in quantity of melted Ti. The observed spectral regions contained the emission peaks of neutral Ti and Mn. Very few emission lines of Al were observed, because they require higher excitation energies compared to Ti and Mn. Boltzmann linearization using Ti emission peaks allowed the estimation of vapor temperature to be between 5000 and 6000 K, except for the welds with the beam offset on Al.
关键词： titanium,Laser,aluminum,emission spectroscopy,dissimilar welding
更新于2025-09-23 15:19:57
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Understanding root humping in high-power laser welding of stainless steels: a combination approach
摘要： High-power laser welding is an efficient way for joining the thick plates in the industries. However, full penetration laser welding of thick plates is prone to form weld imperfections such as undercuts, root humps, and porosity. In this paper, numerical simulation and laser welding experiments are combinedly carried out to investigate the dynamics of the keyhole and molten pool and understand the formation mechanism of root humping during full penetration fiber laser welding of thick stainless steel plates. Besides, the microstructure of the welded joint is analyzed. Good agreements are obtained between the numerical simulation and experimental results. The results indicate that recoil pressure, surface tension, and gravity are the main driving forces for the formation of root hump. The melt flow driven by the recoil pressure near the bottom of the keyhole is an initial and direct formation cause of the root hump. Welding speed is an important factor for the growth of root hump. Local solidification of the rear weld pool path is a hinder for the continuous growth of root hump and can cause a periodic root humping weld.
关键词： Laser welding,Numerical simulation,Root hump,Weld pool,Keyhole
更新于2025-09-23 15:19:57
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A pathway to mitigate macrosegregation of laser-arc hybrid Al-Si welds through beam oscillation
摘要： Macrosegregation is rather serious during laser-arc hybrid welding (LAHW) due to poor arc penetration ability. Here we presented a simple and effective method to improve solute transfer and mitigate macrosegregation by using beam oscillation. When oscillating amplitude A ≥0.8 mm and frequency f ≥ 300 Hz, the macrosegregation of the overall weld cross-section was 300% lower than that of the non-oscillation weld, and the longitudinal section reduced by 220%. The reduction of macrosegregation was attributed to the stirring and vortex suction effect produced by high-frequency oscillating beam, which improved turbulent ?ow and the convection of molten pool to homogenize the alloying elements of hybrid weld.
关键词： Solute transfer,Element distribution,Laser-arc hybrid welding,Beam oscillation,Macrosegregation
更新于2025-09-23 15:19:57
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Analysis of back-weld spatters in laser welding of CP-Ti
摘要： The laser welding of commercial grades of pure titanium plate TA2 with 0.5 mm was taken, and the back area of the molten pool was photographed by high-speed camera. Also, the reasons of back spatters were studied. Spatters on the back side of the plate have three main types: continuous spatters, periodic spatters and no spatters. All continuous back spatters are accompanied by the appearance of keyhole, and the keyhole can be observed at the moment when periodic spatters appear. The downward shear stress applied by the downward jet of metal vapor from the keyhole is an important reason for backside spatter. Increased laser power or welding speed will increase shear force, eventually contributing to more spatters. When the defocused distance is increased to 30 mm, the keyhole is completely obscured on the back side, so there is no spatter at this time.
关键词： Backside spatter,Laser welding,Keyhole behavior,Commercial pure titanium
更新于2025-09-23 15:19:57
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Effect of single pulsed picosecond and 100 nanosecond laser cleaning on surface morphology and welding quality of aluminium alloy
摘要： Removing the oxide film and dirt on the surface of the aluminium alloy can improve the welding quality of the aluminium alloy. In this paper, the characteristics of picosecond and 100 nanosecond pulsed laser cleaning aluminium alloys are explored by changing the average laser power, spot overlap ratio and scanning trajectory overlap rate. The results show that the oxide laser removal depth and diameter are related to the average power. As the average laser power increases, the depth and diameter of the ablation pit increase. At the same average power, the nanosecond laser ablation depth is greater than the picosecond laser. To achieve good surface quality, the nanosecond laser requires a higher overlap rate than the picosecond laser. The high overlap rate results in a nanosecond laser cleaning efficiency that is much lower than that of a picosecond laser. More importantly, the surface quality obtained by picosecond laser cleaning is much better than nanosecond laser cleaning. In addition, the welding experiment shows that the laser cleaning pre-treatment can effectively improve the welding quality.
关键词： Welding quality,Surface micromorphology,Picosecond laser,Laser cleaning,Process strategy
更新于2025-09-23 15:19:57
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In situ chemical composition analysis of a tungsten-inert-gas austenitic stainless steel weld measured by laser-induced breakdown spectroscopy
摘要： The chemical composition of a weld metal determines the resulting solidification mode of stainless steel and the consequent weld metal quality. In this work tungsten inert gas (TIG) welding of EN grade 1.4435 austenitic stainless steel was monitored using laser-induced breakdown spectroscopy (LIBS) for the in situ measurement of chemical composition changes. This research aims to prototype a real-time chemical composition analysis system for welding applications and prove the feasibility of such quality control loop. LIBS was used to investigate in situ the monitoring of metal vaporization during TIG welding. We found Mn vapor formation above the weld pool and subsequent condensation of Mn on the weld metal surface using LIBS. Post-weld line scans were conducted by LIBS on various welds produced with different welding currents. Local changes of Ni and Mn were observed at higher welding currents. The results are in good agreement with the literature and proved that LIBS can be used in situ to inspect the TIG welding process.
关键词： LIBS,In situ measurement,Metal vapor,Welding,Austenitic stainless steel
更新于2025-09-23 15:19:57