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ANALYSIS OF THE PROPERTIES OF AW2099 ALUMINIUM-LITHIUM ALLOY WELDED BY LASER BEAM WITH AW5087 ALUMINIUM-MAGNESIUM FILLER MATERIAL
摘要： EN AW2099 aluminium lithium alloy, 2.0 mm in thickness, was used as an experimental material. EN AW2099 belongs to the 3rd generation of aluminium lithium alloys. The third generation was developed to improve the disadvantages of the previous generation, such as anisotropy in mechanical properties, low fracture toughness, corrosion resistance and resistance to fatigue crack growth, as well. Aluminium magnesium 5087 ?ller wire with a diameter of 1.2 mm was used for the welding. Crack free weld joints were produced after an optimization of welding parameters. The microstructure of weld metal and mechanical properties of weld joints were investigated. Equiaxed zone (EQZ) was observed at the fusion boundary. The character of grains changed in the direction towards the weld centre, from the columnar dendrite zone to equiaxed dendrite zone in the weld centre. The microstructure of the weld metal matrix consisted of α-aluminium. Alloying elements enrichment was found at the inter-dendritic areas, namely copper and magnesium. The microhardness decrease in the weld metal due to a dissolution of strengthening precipitates was measured. The microhardness was slightly higher in comparison to a weld produced by a laser welding without a ?ller material. The tensile strength of the weld joint reached around 67 % of the base material’s strength and the fracture occurred in the weld metal.
关键词： electron microscopy,microstructure,Aluminium lithium alloy,laser beam welding,equiaxed zone,mechanical properties
更新于2025-09-23 15:19:57
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Over 10% Efficient Pure CZTSe Solar Cell Fabricated by Electrodeposition with Ge Doping
摘要： The fabrication of kesterite CZTSe solar cells with electrodeposition method provides an attractive approach for the low-cost and environmental-friendly energy supply, yet the highest conversion efficiency for such solar cells (around 9%) still far away from the highest efficiency of Cu-based kesterite solar cells. Here a 10.54% efficiency CZTSe solar cell (0.28 cm2 active sized area, without anti-reflection layer) is reported through introducing electrodeposited Cu-Ge alloy layer at the bottom of metal precursor. It is found that the presence of Ge element within the bottom of the film can promote downwards diffusion of Sn element. Consequently, the distribution of Sn is relatively homogeneous during annealing process, thus the formation of undesirable defect clusters is inhibited and the band alignment of CdS/CZTSe interface is optimized. As a result, the conversion efficiency of CZTSe thin film solar cells is increased from 6.74% to 10.54%, which is the highest efficiency reported for electrochemically fabricated CZTSe solar cells.
关键词： Cu-Ge alloy,solar cell,electrodeposition,CZTSe
更新于2025-09-23 15:19:57
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FIB-SEM Investigation of Laser-Induced Periodic Surface Structures and Conical Surface Microstructures on D16T (AA2024-T4) Alloy
摘要： The use of aluminum alloy AA2024-T4 (Russian designation D16T) in applications requiring a high strength-to-weight ratio and fatigue resistance such as aircraft fuselage often demands the control and modification of surface properties. A promising route to surface conditioning of Al alloys is laser treatment. In the present work, the formation of ripples and conical microstructures under scanning with femtosecond (fs) laser pulses was investigated. Laser treatment was performed using 250 fs pulses of a 1033 nm Yb:YAG laser. The fluence of the pulses varied from 5 to 33 J/cm2. The scanning was repeated from 1 to 5 times for different areas of the sample. Treated areas were evaluated using focused ion beam (FIB)- scanning electron microscopy (SEM) imaging and sectioning, energy-dispersive X-ray (EDX) spectroscopy, atomic force microscopy (AFM), and confocal laser profilometry. The period of laser-induced periodic surface structures (LIPSS) and the average spacing of conical microstructures were deduced from SEM images by FFT. Unevenness of the treated areas was observed that is likely to have been caused by ablation debris. The structural and elemental changes of the material inside the conical microstructures was revealed by FIB-SEM and EDX. The underlying formation mechanisms of observed structures are discussed in this paper.
关键词： femtosecond laser,LIPSS,conical microstructures,aluminum alloy 2024
更新于2025-09-23 15:19:57
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Effect of Laser Positioning on the Microstructure and Properties of NiTi-Copper Dissimilar Laser Welds
摘要： Dissimilar pulsed laser welding of 400-lm NiTi and Cu wires was used to investigate the effect of laser positioning on NiTi-Cu joint performance. Laser positioning was found to have a significant role in the microstructure due to the difference in mixing patterns and composition distributions. Homogenous element distribution was observed in both the NiTi offset and the centerline joints, while complex mixing patterns were observed in the Cu offset joints. Changing the laser position resulted in a change in alloy content in the weld pool that affected the mixing patterns, and the phases that were formed in the weld zone of each sample. By moving the laser beam from NiTi toward Cu, NiTi and NiTiCu in the weld zone were replaced by pure Cu which resulted in a decreased average hardness from 512 to 158 HV. However, high hardness values were found inside the weld zone of Cu offset welds due to the presence of hard and brittle ternary intermetallic compounds. The 100-lm Cu offset joint displayed the worst mechanical response due to its inhomogeneous microstructure and the presence of cracks and pores. It was shown that positioning the laser beam on the NiTi or on the centerline resulted in a better transition in microstructure that led to acceptable mechanical properties without optimizing laser parameters or inserting any interlayers.
关键词： dissimilar welding,copper,laser welding,laser positioning,shape-memory alloys,NiTi alloy
更新于2025-09-23 15:19:57
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Hot cracking in autogenous welding of 6061-T6 aluminum alloy by rectangular pulsed Nd:YAG laser beam
摘要： Due to high hot crack susceptibility of Al-Mg-Si alloys, autogenous welding by rectangular pulsed laser beam has not been generally successful in the removal of cracks. In this research, the effect of pulsed Nd:YAG laser parameters and preheating on the creation of hot cracks in the 6061-T6 aluminum alloy was investigated. The sample that was fabricated by the laser parameters including 1 Hz, 0.12 mm/s, 10 ms, and without preheating exhibited the highest cooling rate and the smallest dendrite arm spacing but no hot crack was observed. The tensile test specimens of this sample fractured at a point far from the weld metal and a decrease in the precipitation of silicon and magnesium in the inter-dendritic space and the reduction of thermal stresses resulted in the elimination of hot cracks. However, according to macro-scale models for the creation of hot cracks, preheating decreased the tensile stresses in the BTR (brittle temperature range), but increasing the preheating temperature led to increasing rather than decreasing the hot crack length. In this case, the formation of hydrogen porosity, the segregation of silicon and magnesium, and the creation of low melting point compounds were the important parameters affecting the hot crack initiation and growth.
关键词： Laser welding,6061 aluminum alloy,Stress simulation,Solidification microstructure,Hot crack modeling,Rectangular pulse
更新于2025-09-23 15:19:57
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Surface and subsurface characteristics of laser polished Ti6Al4V titanium alloy
摘要： This paper aims at investigating the effects of laser power, laser pulse repetition rate and scan speed on the polished metal surface and subsurface characteristics. The influence of initial surface roughness of workpiece on the polishing performance was also taken into account. In this study, Ti6Al4V titanium alloy was selected as a specimen to be polished by a nanosecond pulse laser. The results revealed that the surface roughness was able to be improved by about 43% when the laser fluence of 1–3 J/cm2 was applied. In addition, the proper polishing condition was dependent on the initial surface roughness of workpiece, and a better surface improvement was subjected to a lower initial surface roughness. A thick recast layer, high degree of oxidation and large heat-affected zone with lots of micro-cracks were obtained when too high laser power and slow scan speed were used in the polishing of titanium alloy. With regard to the findings of this study, the suggested polishing conditions could be applied for smoothing the different levels of initial surface roughness of titanium alloy and possibly other similar metals with less subsurface damage.
关键词： Surface roughness,Polishing,Titanium alloy,Laser
更新于2025-09-23 15:19:57
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Probing a novel heat source model and adaptive remeshing technique to simulate laser powder bed fusion with experimental validation
摘要： A finite element method based three-dimensional heat transfer model with adaptive remeshing is presented to simulate the building of multiple tracks and layers in laser powder bed fusion of metallic powders with enhanced computational competence. A dimensional analysis is undertaken to define the heat source dimensions as function of laser parameters and properties of alloy powder. The computational model is used to calculate the melt pool cross sections for multiple combinations of laser power and scanning velocities considering multi-track-multi-layer builds of SS316L powder. The computed results are verified extensively with the corresponding experimentally measured ones. The model is utilized further to examine its ability to predict defects such as melt track discontinuity and incomplete fusion between neighboring tracks and layers. Overall, the adaptive remeshing and the proposed heat source expression could significantly enhance the model competence by reducing the computational time and memory while maintaining the accuracy of results in simulating laser powder bed fusion of multiple tracks and layers.
关键词： Selective laser melting (SLM),Pool dimensions,Adaptive remeshing,Laser powder bed fusion (L-PBF),Melt pool defects,SS316L alloy
更新于2025-09-23 15:19:57
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Effect of processing parameters on the size of molten pool in GH3536 alloy during selective laser melting
摘要： A combination of the finite element simulation and experimental measurement is proposed to study the influence of laser power and scanning velocity on the molten pool size in the selective laser melting (SLM) of GH3536 alloy. The results show that line energy density and molten pool size exhibit linear growth relationship within the scope of the study parameters. In addition, several GH3536 alloy samples are fabricated by SLM technology with different parameters. All SLM samples are used for metallographic experiment to measure the molten pool size. The result shows that experimental measurements are in good agreement with the simulation predictions.
关键词： molten pool size,experimental measurement,finite element simulation,GH3536 alloy,selective laser melting
更新于2025-09-23 15:19:57
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Light incoupling and SPR tailoring of graphene coated silver-aluminum alloys’ dimer in mimicked humid ambient
摘要： This work demonstrates the optical responses of the graphene coated silver-aluminum (Ag-Al) alloys' dimer in the presence of humid ambient using Discrete Dipole Approximation (DDA) as a numerical technique. The non-equivalent spherical shape of graphene coated Ag-Al alloy dimer has been considered for this study, where the plasmonic coupling supports both the bonding and anti-bonding modes which lies in higher and lower wavelength region, respectively. The combined effect of these modes provides a broad resonant spectrum, which is mainly influenced by the inter-particle separation between graphene coated alloy dimer. As the interparticle separation decreases, the resonance wavelength shows a red spectral shift with increase in the magnitude of local electric field. The results of proposed geometry provide a good support for the various applications in photovoltaics and photonics.
关键词： surface plasmon,humidity,graphene,dimer,Silver-aluminum alloy
更新于2025-09-19 17:15:36
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High Reliability of Ag Reflectors with AgCu Alloy for High Efficiency GaN-Based Light Emitting Diodes
摘要： We propose an Ag reflector layer with an AgCu alloy layer as a thermally reliable reflector for high power flip-chip and vertical light emitting diodes (LEDs). By annealing the deposited Ag and Cu layers, intermixed grains and grain boundaries from the alloyed AgCu layer were formed on the LEDs, and CuO nano dots precipitated at the grain boundaries. A thick AgCu layer was deposited to cover the AgCu alloy layer. The precipitation of the CuO nano dots at the grain boundaries suppressed Ag agglomeration, leading to enhanced light reflectance after the annealing process. Consequently, the alloyed AgCu/Ag reflector produced by annealing at a high temperature of 500 °C demonstrated a higher reflectance of 78% and a lower contact resistance of 7.0 × 10^{-5} Ω·cm2.
关键词： Light Emitting Diode,AgCu Alloy,Reflector,Nano Dots,Ohmic Contact
更新于2025-09-19 17:15:36