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On the occurrence of weld bead porosity during laser vacuum welding of high pressure aluminium die castings
摘要： Due to porosity and incomplete fusion, aluminium high pressure die castings are materials that are known to be difficult to weld. Hereby porosity is mainly caused by hydrogen which is trapped within the weld bead during solidification as a result of insufficient degassing. To enhance degassing and to reduce the influence of surrounding air, laser vacuum welding was applied within the current study. The main goal was to investigate the occurrence of porosity during laser beam welding of aluminium high pressure die castings. To reach this aim, die casting plates were laser welded at varied ambient pressure and investigated by x-ray computed tomography. The analysis of the welds focuses on the size, position, amount and shape of the detected defects depending on the ambient pressure during welding. The results showed a dependency of the occurrence of porosity and the ambient pressure whilst welding.
关键词： Aluminium die castings,Laser vacuum welding,Aluminium,X-ray computed tomography,Laser welding,Porosity
更新于2025-09-12 10:27:22
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Single track scanning experiment in laser powder bed fusion process
摘要： Laser powder bed fusion (LPBF) process utilizes laser source to melt the powder particles. As a result, melt pool is formed which develops along the scan track. In this study, single track scanning with Ti-6Al-4V alloy is performed in alternate layers over the supporting base pad. Multiple single scan tracks with scanning speeds of 200mm/s, 400 mm/s and 600 mm/s are defined and thermal responses are captured using infrared camera. The thermal images record the apparent temperature measurements; therefore, derivate method is used to find the liquidus-solidus transition region which is required to estimate the melt pool length and width. Based on the estimation, the average melt pool width of the single track decreased with increasing speed while the average melt pool length for 200 mm/s scanning speed was 438.62 μm, for 400 mm/s was 432.27 μm and for 600 mm/s was 451.2 μm. Besides, cylindrical powder container samples with enclosed single tracks were designed to investigate internal features using computed tomography (CT). The CT images showed that the scanning speed of 200 mm/s and 400 mm/s resulted in formation of significant number of pores due to keyhole formation which may contribute to variation in melt pool length.
关键词： Thermal image,Single track,Infrared Camera,Porosity,Melt pool
更新于2025-09-12 10:27:22
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Porosity and solidification cracking in welded 45 mm thick steel by fiber laser-MAG process
摘要： Porosity and solidification cracking in joining of thick sections are very common issues in deep penetration keyhole laser-arc hybrid welding (LAHW). In the present work, 45 mm thick high strength steel was joined by a double-sided technique. With combined use of fast welding speeds and larger air gap between plates, higher amount of porosity was found because of the dynamic behavior of the keyhole walls. Solidification cracking formed at the centerline in the bottom of the weld due to high-depth-to-width geometrical ratio. Numerical simulations have been performed and showed very high cooling rate and stresses occurred in the root of the deep welds, which corresponds with higher cracking tendency.
关键词： hybrid welding,mechanical properties,porosity,Laser welding,thick steel,solidification cracking
更新于2025-09-12 10:27:22
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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
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Mitigation of porosity defects in fiber laser welding under low vacuum
摘要： Laser welding trials were conducted under low vacuum to reduce porosity defects. The effect of vacuum on the characteristics of porosity was quantitatively evaluated using 3D micro-CT. To explore the mechanisms of porosity formation at atmospheric pressure and porosity defects mitigation under vacuum, the weld pool and fluid flow behaviors were directly observed by placing a transparent glass plate on one side of the weld pool. The results showed that the vacuum condition was favorable for reducing porosity, especially process porosity. It was also found that the weld pool size and fluid flow were totally different at atmospheric pressure and under vacuum. At atmospheric pressure, bubbles were trapped in the vortex induced by two opposing fluid flows, failed to escape from the weld pool and finally formed pores. Under vacuum, suppression of vapor plume and reduction in the boiling point led to a deeper keyhole and a thinner weld pool, resulting in an upward flow in the rear weld pool. In this case, the bubbles could escape easily from the weld pool with the help of the upward flow.
关键词： 3D micro-computed tomography,Fluid flow,Low vacuum,Laser welding,Porosity,Ambient pressure
更新于2025-09-12 10:27:22
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Efficiency and Stability Enhancement of Fully Ambient Air Processed Perovskite Solar Cells Using TiO <sub/>2</sub> Paste with Tunable Pore Structure
摘要： Crystallization and nucleation of the perovskite layer in the mesoscopic perovskite solar cells (PSCs) depend on the nucleation sites of the electron transport layer (ETL). The porosity optimization of TiO2 film as an efficient ETL plays an important role in the performance improvement of PSCs. In the present study, nontoxic carbon spheres synthesized with uniform morphology and controllable size under hydrothermal conditions and used as a template to generate the tunable porous TiO2 films. Furthermore, the effect of porosity modification of TiO2 on the formation of perovskite films with large grain size is studied in an ambient atmosphere with humidity higher than 50%. The best TiO2 film is produced with carbon spheres 8 wt% (C8), which results in the formation of a pinhole-free, and compact-packed perovskite layer. The fully air processed PSC device with the ETL made of C8 film exhibits an efficiency of 16.66% with reduced hysteresis, which is much superior in performance compared to the standard cell (11.72%). It is believed that this porosity optimization of TiO2 layer is a simple practical strategy for improved stability of fully air processed efficient perovskite solar cells and usable for the fabrication of reproducible compact perovskite layers in uncontrolled laboratories.
关键词： porosity,AP-VASP,carbon sphere,mesoporous TiO2,perovskite solar cells
更新于2025-09-12 10:27:22
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High-nitrogen steel laser-arc hybrid welding in vibration condition
摘要： Welding porosity and nitrogen content are considered significant factors affecting the mechanical properties of fusion-welding joints of high-nitrogen steel. In this study, a method of applying mechanical vibration in the welding process to reduce weld porosity and increase weld nitrogen content was investigated. The effects of mechanical vibration on porosity, tensile, and impact properties were analysed. The results indicated that the bubble floating speed in the vibrating weld pool is faster than that in the general welding mode. With the increase of mechanical vibration frequency, the porosity of the weld decreased at first and then rose. The tensile strength and impact energy increased first and then decreased, and the fracture surface indicated a ductile fracture.
关键词： nitrogen content,vibration,porosity,austenitic stainless steel,high-nitrogen steel,Laser-arc hybrid welding,microstructure,mechanical properties
更新于2025-09-12 10:27:22
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Effect of Hot Isostatic Pressing on Al-10%Si-0.4%Mg Alloy Fabricated by Selective Laser Melting; レーザ積層造形により作製したAl-10%Si-0.4%Mg合金における熱間等方加圧処理の影響;
摘要： In this study, we investigated the effects of hot isostatic pressing (HIP) on the mechanical properties of an Al-10%Si-0.4%Mg alloy fabricated by selective laser melting (SLM). In addition, the effect of internal porosity on the mechanical properties of the alloy was also investigated. After the HIP, the internal porosity of the alloy decreased, while its elongation to failure (EL) improved significantly. However, the 0.2% proof stress (PS) and the tensile strength (TS) of the HIPed alloy were significantly lower than those of the as-built state. This can be attributed to the microstructural changes that occurred at elevated temperatures during the HIP. In addition, the PS and TS of the as-built alloy decreased with an increase in the internal porosity. On the other hand, in the case of the HIPed alloy, the PS and TS were not affected by the internal porosity. However, EL was sensitive to the internal porosity. The EL of the HIPed alloy decreased with an increase in its initial internal porosity. This is because the diffusion bonding during the HIP was imperfect owing to the presence of oxidized scales. Hence, it is imperative to optimize the laser irradiation conditions for the fabrication of aluminum alloy by SLM.
关键词： aluminum alloy,selective laser melting (SLM),hot isostatic pressing (HIP),additive manufacturing (AM),internal porosity
更新于2025-09-11 14:15:04
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Study of the porosity generated by the use of cutting fluid in hybrid processes combining machining and Laser Metal Deposition (LMD)
摘要： The use of hybrid manufacturing processes that combine additive and machining operations is on increase and an example of it is the fact that the most advanced machine tool manufacturers have developed hybrid machines solutions. Nevertheless, cutting fluid required for machining operations can present several problems for the Laser Metal Deposition (LMD) process. In order to solve this issue, the present work evaluates the influence of the coolants in the LMD process from the point of view of pore generation and clad quality. For this purpose, several tests are performed on a part impregnated with cutting fluid, both directly and after the elimination of the fluid by means of different alternatives.
关键词： additive manufacturing,cutting fluid,laser metal deposition,porosity,coolant,clad quality,lubricant,hybrid machines
更新于2025-09-11 14:15:04
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Molybdenum incorporated Cu1.69ZnSnS4 kesterite photovoltaic devices with bilayer microstructure and tunable optical-electronic properties
摘要： Molybdenum (Mo) incorporated Cu1.69ZnSnS4 (CZTS) absorber has been deposited onto Mo-coated soda lime glass (SLG) by co-sputtering of Mo and non-stoichiometric quaternary compound targets. After sulfurization at 600 °C, Mo incorporation into CZTS was confirmed by X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). From the observed shifts for the (1 1 2) and (2 2 0) peaks, both lattice parameters a and c of the CZTS unit cell were found to decrease with increasing Mo incorporation suggesting cationic substitution by Mo. The Mo incorporated CZTS has a bilayer microstructure in which the lower sub-layer adjacent to the substrate has a smaller grain size and higher porosity than the upper sub-layer. The lower sub-layer is also richer in Mo and has a graded Mo profile. Sheet resistance measurements on Mo incorporated CZTS films deposited on SLG and on quartz show resistivity that decreases with the amount of Mo in CZTS and Mo acts as an acceptor dopant. The energy band gap of CZTS on SLG increases from 1.38 eV to about 1.68 eV as a result of Mo incorporation and the absorbance of Mo incorporated CZTS is increased for wavelengths shorter than 600 nm. When Mo is co-deposited at the optimized DC sputtering power of 10 W, Mo incorporated CZTS/CdS solar cells attain a maximum power conversion efficiency (PCE) of 5.49% versus 1.63% for the reference device under 1 Sun AM 1.5 illumination. Device efficiency enhancement is due to back surface field, increased carrier concentration and reduced band tailing.
关键词： Kesterite solar cell,porosity,Molybdenum,Bilayer microstructure,Co-sputtering
更新于2025-09-11 14:15:04