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Dynamic keyhole behavior and keyhole instability in high power fiber laser welding of stainless steel
摘要： A three-dimensional numerical model, considering the real-time multiple reflections of a laser beam, adiabatic bubble model and shear stress, was developed to study the dynamic keyhole behavior and keyhole instability in fiber laser welding of stainless steel. The inner dynamic keyhole behavior and weld defect formation were directly observed in a high resolution assisted by transparent glass. The numerical and experimental results showed that the keyhole width reached the quasi-steady state earlier than the keyhole depth did during fiber laser welding of stainless steel. Due to the large recoil pressure at rear keyhole wall caused by the irradiation of laser energy reflected by the bulge at the front keyhole wall, the rear keyhole wall was severely deformed at keyhole bottom and keyhole middle. The rear keyhole wall was collapsed due to the high surface tension pressure and hydrostatic pressure. The whole keyhole collapse was attributable to the capillary instability of the keyhole associated with large depth/width ratio and the strong flow of the bulges at the keyhole wall. When the laser power was increased, the keyhole depth/width ratio was increased, so the keyhole was more capillary instable. The average inclined angle of the front keyhole wall was decreased.
关键词： Bubble formation,Dynamic keyhole behavior,Keyhole instability,Fiber laser welding
更新于2025-11-28 14:24:20
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Effect of Heat Input on Porosity Defects in a Fiber Laser Welded Socket-Joint Made of Powder Metallurgy Molybdenum Alloy
摘要： Porosity defects are still a challenging issue in the fusion welding of molybdenum and its alloys due to the pre-existing interior defects associated with the powder metallurgy process. Fiber laser welding of end plug and cladding tube made of nanostructured high-strength molybdenum (NS-Mo) alloy was performed in this work with an emphasis on the role of welding heat input. The distribution and morphology of porosity defects in the welded joints were examined by computed tomography (CT) and scanning electron microscopy (SEM). Preliminary results showed that laser welding of NS-Mo under low heat input significantly reduced the porosity defects in the fusion zone. The results of computed tomography (CT) showed that when the welding heat input decreased from 3600 J/cm (i.e., 1200 W, 0.2 m/min) to 250 J/cm (i.e., 2500 W, 6 m/min), the porosity ratio of the NS-Mo joints declined from 10.7% to 2.1%. Notable porosity defects under high heat input were related to the instability of the keyhole, expansion and the merging of bubbles in the molten pool, among which the instability of the keyhole played the dominant role. The porous defects at low heat input were generated as bubbles released from the powder metallurgy base metal (BM) did not have enough time to overflow and escape.
关键词： fiber laser welding,molybdenum alloy,porosity defects,heat input
更新于2025-11-28 14:24:20
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Influence of laser parameters on tensile shear strength of copper welds
摘要： The electrification of the power train in the automotive industry leads to the requirement of electrical connectors with high ampacities. These connectors are often realized using ultrasonic bonding technology. Substitution of ultrasonic welding by laser welding allows an increase of ribbon cross section by a factor of 5 and thus a similar increase of the maximum transferred current. The increased cross section leads to higher loads (at least by a factor of 5) applied to the weld seam during the process. To minimize the heat input, the weld seam strength in shear direction shall be maximized. The influence of different laser parameters on the ultimate tensile shear stress in lap joint configuration is investigated, based on representative specimen geometries (10 × 0.3 mm2). The variable parameters are: laser wavelength (IR around 1050 nm + frequency doubled 515 nm), focal diameters (42–300 μm), different temper conditions of the base material, process parameters (laser power 0.6–4 kW and feed rate 50–800 mm/s), and welding strategies (single pass welding, spatial beam modulation). The material used is Cu-ETP (>99.9% Cu). For all the investigated parameters, the observed failure mode is “fracture in the fusion zone.” The ultimate tensile shear stress for all experiments is around 188 N/mm2 even for parameter changes in the order of one magnitude. This is in contrast to the assumed relation between laser parameters and the mechanical properties. This contrast will be discussed.
关键词： load-carrying capacity,ductile welds,wobbling,fiber laser welding,shear strength
更新于2025-11-28 14:24:20
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Influence of Al-Si coating on microstructure and mechanical properties of fiber laser welded 22MnB5 steel
摘要： Fiber laser welding of as-received 22MnB5 steel with Al-10wt.%Si coating in butt configuration was performed. The influence of Al-Si coating on microstructure transformation and mechanical properties including tensile tests, fatigue tests and Erichsen cupping tests was investigated. Ferrite with Al enrichment (1.37 wt%) was found in the fusion zone (FZ) of coated welded joints with 15% area proportion, while nearly entire martensite structure composed the FZ in the case of de-coated joint. The strain localization was more likely to accumulate at the martensite/martensite interface rather than the ferrite/martensite interface due to the higher kernel average misorientation (KAM) values. Microhardness of the FZ in coated welded joints dropped by 50HV compared with that of de-coated welded joints. However, tensile properties were not affected since failure occurred at base metal (BM). Fatigue samples of coated welded joints showed better performance than the de-coated ones, suggesting that the ferrite in the FZ had positive effect on fatigue lives under cycling load conditions. The Erichsen cupping tests showed similar Erichsen values (5.60 mm and 5.67 mm) for de-coated and coated welded joints. An opposite effect of ferrite on Erichsen cupping tests was obtained. The peak force required for deformation dropped by 35% with Al-10wt.%Si coating.
关键词： Microstructure,Al-Si coating,Mechanical properties,Fiber laser welding,22MnB5 steel
更新于2025-11-28 14:24:20
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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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Effect of fiber laser welding on solute segregation and proprieties of CoCrCuFeNi high entropy alloy
摘要： The effect of fiber laser welding on solute segregation and proprieties of CoCrCuFeNi high entropy alloy was investigated. The microstructure and mechanical properties of the parent metal and the fusion zone were comparably studied. The parent metal was dendrite, with elemental Cu segregated to interdendrites owing to small bonding energies with Fe, Co, Ni, and Cr atoms. After laser welding, the microstructure in the center of the fusion zone was predominantly equiaxial grains, whereas that in the edge region was mainly columnar crystals oriented perpendicular to the fusion line. The segregation of Cu in the fusion zone is alleviated by grain refinement and molten pool agitation. Because of the fine-grain strengthening and precipitation hardening effect, the hardness and yield stress of the fusion zone are 12.84% and 26.87% greater than those of the parent metal, respectively.
关键词： CoCrCuFeNi,mechanical properties,fiber laser welding,solute segregation
更新于2025-09-23 15:19:57
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High Power Fiber Laser Welding with Filler Material
摘要： Industry today is continually challenged to improve quality, reliability, reduced cycle times, and improve the overall manufacturing efficiency. This is driving manufacturers across various market sectors to consider fiber laser welding and the possibility to automate their welding processes to improve consistency and part quality. Another driver is the changing workforce dynamics. It is hard to find or train skilled workers who can consistently and reliably weld aluminum, titanium, and high-strength nickel alloys. This is particularly true when welding with filler material where the base materials are subject to porosity and cracking during the welding process.
关键词： Fiber Laser Welding,Titanium,Filler Material,Nickel Alloys,Aluminium,Laser Welding
更新于2025-09-19 17:13:59
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Effects of Cr2O3 active agent on the weld process dynamic behavior and joint comprehensive properties of fiber laser welded stainless steel thick plate
摘要： In this study, the dynamic behaviors of metal vapor, plasma, keyhole, and weld pool during activating laser welding of stainless steel thick plates are monitored in real time by employing a novel "sandwich" method in combination with a high-speed camera system. Meanwhile, the welding quality of specimens is inspected and analyzed from the aspects like joint weld formation, mechanical properties, microstructure, and element distribution. The effects of Cr2O3 active agent on the welding stability and quality of specimens are explored. According to the results, adequate coating of active agent on the specimen surface can weaken and suppress the generation and drastic changes of metal vapor and plasma inside and outside the keyhole, increase the keyhole depth, improve the keyhole shape, weaken the oscillation amplitude of weld pool, and prolong the change cycles of keyhole and weld pool. Consequently, the stability of welding process is enhanced, the generation of porosity and splash defects is inhibited preferably, the quality of weld formation is improved, the weld penetration is increased, the grain structure in weld zone is refined, the width of heat affected zone is narrowed, and the joint strength and toughness are enhanced, without showing apparent change of the relative element contents in the welded joint. In conclusion, coating of Cr2O3 active agent on the specimen surface is effective in improving the welding properties of laser welded stainless steel plates.
关键词： Welding quality,Fiber laser welding,Plasma morphology,Cr2O3 active agent,Weld pool behavior
更新于2025-09-19 17:13:59
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Dynamic interaction between a laser beam and keyhole front wall during fiber laser welding
摘要： A bright spot (laser beam spot-center-induced metal vapor) on the keyhole front wall (KFW) was observed during fiber laser keyhole welding of a ‘sandwich’ specimen to reveal the interaction between the laser beam and the KFW. The dynamic behavior of the bright spot shows that the keyhole formation is the result of periodical drilling of the laser beam spot center on the KFW during welding. Welding parameters have little effect on the drilling period. The drilling speed first increases and then decreases with the increase in the keyhole depth, and the next drilling process begins before the drilling speed reduces to 0 m s?1. The average drilling speed can be increased by increasing the line energy or power density of the laser.
关键词： keyhole front wall (KFW),drilling speed,interaction,fiber laser welding,period
更新于2025-09-11 14:15:04