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Numerical and experimental study on keyhole and melt flow dynamics during laser welding of aluminium alloys under subatmospheric pressures
摘要： Porosity defects was highly related to the keyhole and melt flow dynamic during laser welding process. In this paper, a novel 3D numerical model was developed to describe the keyhole dynamic and melt flow behaviors during laser welding of 5A06 aluminium alloy under subatmospheric pressures. The effect of ambient pressure on laser welding process was taken into consideration by optimizing the boiling point of aluminium alloy and recoil pressure of evaporated metallic vapor jets based on vapor–liquid equilibria calculation and Wilson equation. A moving hybrid heat source model was employed to describe the laser energy distribution under subatmospheric pressures. Numerical results indicated that a wider and deeper keyhole with less humps was produced under subatmospheric pressure comparing with that of atmospheric pressure. The vortices in the rear keyhole wall became unapparent or even disappeared with the decrease of ambient pressures. The melt flow velocity on the keyhole wall was larger under a lower pressure. A smaller difference between boiling point and melting point was produced and this led to the formation of a thinner keyhole wall and improved the stability of molten pool. Larger recoil pressure produced under subatmospheric pressure was responsible for the weakened vortices and enhanced melt flow velocity. Bigger keyhole opening size, larger melt flow velocity, thinner keyhole and the weakened vortices all resulted into the reduction of porosity defects during laser welding of aluminium alloys. Based on the simulation results, the plasma distribution, weld formation and porosity defects had been demonstrated. The compared results showed that the simulation results exhibited good agreements with the experimental ones.
关键词： Porosity defects,Keyhole stability,Numerical simulation,Subatmospheric pressure,Melt flow dynamic,Laser welding
更新于2025-11-28 14:24:20
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The influence of Marangoni effect on the growth quality of multi-crystalline silicon during the vacuum directional solidification process
摘要： A multi-field coupling model of heat-flow-thermal stress was established to investigate the influence of Marangoni effect on the growth quality of multi-crystalline silicon (mc-Si) during the vacuum directional solidification (VDS) process. The simulation results showed that the Marangoni effect has a significant effect on the distribution of temperature and thermal stress as well during the VDS process due to the increased velocity of melts. The enhanced flow incurred more homogeneous temperature distribution of silicon melts and reduced radial temperature gradient, which then leads to the flatter solid/liquid (s/l) interface. However, as temperature gradient of the crystal increased, thermal stress of the silicon ingot was strengthened as a result. The growth quality of crystal was more desirable when adopting a pulling-down rate of 10 μm/s, in which case the (111) surface was advantageous throughout the entire crystal growth process by XRD detection. Finally, the reliability of the numerical simulation result was verified by the experiment.
关键词： Multi-crystalline,Melt flow,Vacuum directional solidification,Numerical simulation,Marangoni effect
更新于2025-09-23 15:22:29
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Role of thermal fluid dynamics in alloying element distribution and weld porosity in powder feeding-based laser welding of Al alloy
摘要： This work develops a model incorporating the powder transport, laser heating, and molten pool dynamics to describe the mixing process of alloying element and reveal the mechanisms of bubble dynamics in powder feeding-based laser welding. Simulation results show that the different roles of recoil pressure: driving the molten metal flow at the rear part of keyhole in partial penetration and maintaining the stable keyhole profile in full penetration, are responsible for the difference between their melt flow behaviors. Driven by the melt flow, the alloying element transport path can be generalized as the shallow areas, the rear areas, the central and bottom areas in partial penetration. It permits a relatively uniform silicon distribution. However, two vortices rotating in the opposite direction in full penetration results in a higher concentration of Si in the upper part. Meanwhile, we conclude three steps for the bubble dynamics: bulge formation, bubble formation, bubble being captured by re-formed keyhole or being captured by the solid-liquid interface or escaping from the free surface. Such phenomena manifest that the contributions to the processing quality and metallurgy quality of welded joints come from the complex melt flow behaviors, which are confirmed by a series of experiments.
关键词： Thermal fluid dynamics,Alloying element distribution,Melt flow,Powder feeding-based laser welding,Weld porosity
更新于2025-09-23 15:19:57
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In-situ full-field mapping of melt flow dynamics in laser metal additive manufacturing
摘要： Melt flow plays a critical role in laser metal additive manufacturing, yet the melt flow behavior within the melt pool has never been explicitly presented. Here, we report in-situ characterization of melt-flow dynamics in every location of the entire melt pool in laser metal additive manufacturing by populous and uniformly dispersed micro-tracers through in-situ high-resolution synchrotron x-ray imaging. The location-specific flow patterns in different regions of the melt pool are revealed and quantified under both conduction mode and depression mode. The physical processes at different locations in the melt pool are identified. The full-field melt-flow mapping approach reported here opens the way to study the detailed melt-flow dynamics under real additive manufacturing conditions. The results obtained provide crucial insights into laser additive manufacturing processes and are critical for developing reliable high-fidelity computational models.
关键词： x-ray imaging,melt flow,laser processing,powder bed fusion,Metal additive manufacturing
更新于2025-09-12 10:27:22
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Quantitative study of melt flow dynamics inside laser cutting kerfs by in-situ high-speed video-diagnostics
摘要： Within this paper the melt flow dynamics of the laser cutting process during laser cutting of 6 mm thick stainless-steel using a disk laser with a laser power of 5 kW and nitrogen assist gas with a pressure up to 20 bar, is analyzed by in-situ high-speed video-diagnostics (>100,000 fps). An advanced algorithm is used to determine spatially resolved the melt flow dynamics on the laser cutting front. The results reveal a link between the fluid dynamics, the cutting velocity, the assist gas pressure and the average roughness of the cut flank.
关键词： melt flow,process diagnostics,high-speed imaging,1 micron laser,Laser cutting
更新于2025-09-12 10:27:22