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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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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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Surface modification methods for fatigue properties improvement of laser-beam-welded Ti-6Al-4V butt joints
摘要： Surface and internal defects formed upon laser beam welding (LBW) have been recognized as a serious problem because they cause stress concentration leading to premature failure of a welded component. This paper seeks to remedy these weld imperfections by applying various post-weld treatments and analyzing their effect on the high cycle fatigue (HCF) performance of welded joints. High efficiency of laser-based post-processing techniques after welding such as laser surface remelting (LSR) and laser shock peening (LSP) was demonstrated and compared with conventional approaches. The study reveals that welding porosity determines the internal crack initiation of the surface-treated weldments. Influence of process parameters on porosity level and the HCF properties is presented in detail. Based on an extensive experimental study, practical guidelines needed to mitigate the notch effect from defects and to maximize the fatigue performance of the laser-welded Ti-6Al-4V butt joints are given.
关键词： laser shock peening,Laser beam welding,high cycle fatigue,porosity,defects
更新于2025-09-12 10:27:22