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Improvements of Laser Weldability of Aluminum Alloys by Laser Texturization
Abstract
The application of laser beam welding to aluminum alloys has some
complications, mainly due to their high reflectivity, high thermal
conductivity and low viscosity. In order to increase the laser
absorption of aluminum alloys, some surface treatments has been applied
in the literature, such as the application of dark coatings or
sandblasting. However, these conventional superficial treatments have
some drawbacks, such as the low weld penetration, the possibility to
undergo magnesium evaporation and the impossibility to control and/or
change the superficial properties of the treated samples. In the present
contribution, laser texturization treatments have been performed with a
fibber laser for the first time on aluminum alloys to increase their
weldability. These textured samples have shown better weldability than
reference sandblasted samples.
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In this paper, a three-dimensional numerical model was developed to study laser welding in an aluminium alloy (AA5083). The CFD model was used to solve the governing equations of conservation of mass, momentum and energy, so as to obtain the morphology, velocity field and temperature field of the melted zone in steady state. The predicted dimensions of the weld pool agreed well with experimental results obtained on laser conduction welding with a (CW) high power diode laser. The study allowed to determine the effect of different surface treatment (sandblasting, black painting) on the laser absorptivity of the alloy and analyze the heat transfer mechanism within the weld pool
Laser welding is a very attractive technique to join different alloys at the industrial level, due to Its low heat input, high flexibility, high weld quality and high production rate. In this work, the weldability of the aluminium alloy AA 5083 with a high power diode laser has been tested. Concisely, samples were subjected to lineal treatments of laser radiation, with the objective of studying the properties of the bead on plate welds generated. The main objective of the present work has been to study the influence of both the processing rate and the superficial treatment of the AA 5083 samples, on the morphological, microstructural and corrosion properties of the laser weld beads. The sizes of the welds were higher as the processing rate was decreased. The weld beads were seen to have better behaviour against corrosion than the base metal due to the microstructural refinement. It was also verified that a blasting process before processing gave beads with lower size but better corrosion resistance than the application of a black layer, due to the minimisation of the magnesium evaporation In this former superficial treatment
We have prepared absorbing structures for photovoltaic cells with different nano-texturization, obtained by means of a femtosecond laser, without the use of corrosive gas (i.e. under vacuum). To take in account the 3D structured front surface, the emitter doping has been realized by using Plasma Immersion Ion Implantation (so-called PULSION). The results show a photocurrent increase up to 60 % in the laser texturized zones.
We present results on the growth of highly organised, reproducible, periodic microstructure arrays on a stainless steel substrate
using multi-pulsed Nd:YAG (wavelength of 1064 nm, pulse duration of 7 ns, repetition rate of 25 kHz, beam quality factor of
M
2∼1.5) laser irradiation in standard atmospheric environment (room temperature and normal pressure) with laser spot diameter
of the target being ∼50 μm. The target surface was irradiated at laser fluence of ∼2.2 J/cm2 and intensity of ∼0.31×109 W/cm2, resulting in the controllable generation of arrays of microstructures with average periods ranging from ∼30 to ∼70 μm, depending
on the hatching overlap between the consecutive scans. The received tips of the structures were either below or at the level
of the original substrate surface, depending on the experimental conditions. The peculiarity of our work is on the utilised
approach for scanning the laser beam over the surface. A possible mechanism for the formation of the structures is proposed.
Purpose: The aim of the paper is to demonstrate a laser method of multicrystalline silicon texturization. This means creating a roughened surface so that incident light may have a larger probability of being adsorbed into the solar cell. It was demonstrated, that laser processing is very promising technique for texturing multicrystalline silicon independent on crystallographic orientation of grains compared to conventional texturing methods.Design/methodology/approach: The topography of laser textured surfaces were investigated using ZEISS SUPRA 25 scanning electron microscope and LSM 5 Pascal ZEISS confocal laser scanning microscope. The reflectance of produced textures was measured by Perkin-Elmer Lambda spectrophotometer with an integrating sphere. Electrical parameters of manufactured solar cells were characterized by measurements of I-V illuminated characteristics under standard AM 1.5 radiation.Findings: The texturing of multicrystalline silicon surface using Nd:YAG laser makes it possible to increase absorption of the incident solar radiation. Laser processing is a promising method for texturization of multicrystalline silicon compared to conventional texturing methods applied in used technology of solar cells.Research limitations/implications: Laser processing introduce into the bulk of material some unwanted effects, having detrimental influence on the main parameters of processed silicon wafers. Solar cells manufactured from laser-textured multicrystalline silicon wafers demonstrate worse electrical performance than cells manufactured from the non-textured wafers after saw damage removal as well as wafers textured by etching in alkaline solutions. Chemical etching by means of potassium alkali made it possible to increase cell efficiency.Originality/value: Laser texturing has been shown to have great potential as far as its implementatnion into industrial manufacturing process of solar cell is concerned.
We have irradiated silicon with a series of femtosecond laser pulses to improve light absorption of photovoltaic solar cells. The black silicon shows excellent optical properties on mono and multicrystalline silicon wafers with a reflectivity down to 3 %, without crystal orientation dependence. After the laser process, the front side of samples have been boron-implanted by Plasma Immersion Ion Implantation to create the 3D p+ junction. Improved electrical performances have also been demonstrated with a 57 % increase in the photocurrent, compared to the non-texturized surface.
Efficient doping of amorphous silicon(a-Si) is a key issue in the field of photovoltaic applications. In this paper an attempt has been made to produce a highly highly textured Sb doped a-Si. The a-Si were coated with Sb to a thickness of 200nm using vacuum evaporation method and treated with an Nd:YAG laser of 355nm with a threshold fluence of 460mJ/cm2 by overlapping the laser spots to 90% of its size. The samples are retretaed with a low laser fluence of 230mJ/cm2 respectively so as to crytsallize and diffuse the Sb on to the surface and to activate the dopant. The laser doped and subequently laser textured samples were analysed through Scanning Electron microscope (SEM), X-ray diffraction (XRD) & Atomic Force Microscope(AFM).The traces of SiSb in the XRD peak with improved surface roughness were observed on the laser doped samples. This represents that the dopants are highly diffused on the a-Si.
We report the first systematic investigation of texturizing polycrystalline silicon films utilizing an excimer laser to achieve an increased cell capacitance for high-density memory-device applications. The degree of surface roughness after laser processing was found to be sensitive to polycrystalline silicon deposition temperature and laser fluence. In the laser-fluence range of 0.2 to 0.7 J/cm2, the reflectivity of polycrystalline silicon films varied from ∼10% to 80%. A significant increase in the degree of surface roughness was achieved at optimized conditions. This, in turn, resulted in an increased effective surface area of the polycrystalline silicon film used as the capacitor-storage node. Primary capacitance-voltage measurements indicated a 10% increase in the cell capacitance, and current-voltage characterizations showed no device degradation due to laser processing.
The subject of the present paper is to design the technique of laser texturization for solar cells made of multicrystalline silicon and improve understanding of the interaction between laser light and workpiece. We explore how different transverse modes influence laser surface treatment and examine some details related to laser multimodal operation. Since constant increase in global production of photovoltaic power can be observed the new technologies for manufacturing solar cells of improved efficiency are developed. One of the most important factors influencing cells performance is reflectivity of its front side. Consequently, new methods for efficient reduction of reflectance are searched. One of the crucial stages which is carried out to increase solar radiation absorption is surface texturization. It is brought under well control for solar cells made of monocrystalline silicon. However, from the market point of view the reduction of production costs has essential meaning. As a result, the market share of multicrystalline cells systematically grows since the base material is approximately twice cheaper compared to monocrystalline silicon. But on the other hand, texturization methods used for monocrystalline silicon are ineffective in the case of multicrystalline silicon. Thus, it seems to be very interesting to investigate new alternative methods for effective texturization of multicrystalline silicon. One of the promising technologies is laser processing which is the subject of present paper.
Among the newly developed techniques for thin film processing and semiconductor device fabrication, the excimer laser is one of the most promising and powerful due to its usefulness for rapid thermal processing and surface microstructure modification. To date, its applications in microelectronics include deep UV lithography, metal deposition and reflow, process monitoring and diagnostics, laser repairing, and thin film processing including high temperature superconductor material synthesis and laser enhanced chemical vapor deposition (CVD). In this paper, the status of semiconductor device metallization using excimers laser will be reviewed, and recent development in texturization of polycrystalline silicon thin films, silicide formation, and maskless patterning using excimer lasers will be presented.
In this work, samples of aluminium alloys 5083-T0 and 6082-T6 have been welded under conduction regime, using a high power diode laser. The influence of experimental variables, as the laser power and the linear welding rate, on the sizes and properties of the butt weld beads has been studied. In addition to measure the depths and widths of the weld beads, their microstructure, microhardness profile and corrosion resistance have been analysed. The results obtained allow one to define the experimental conditions leading to good quality butt welds with higher penetration than those published in the recent literature under conduction regime. Maximum penetration values of 3 and 2.3 mm were obtained for 5083 and 6082, respectively. Additionally, a simple mathematical expression relating the weld depth (d) with the laser power (P) and the processing rate (v) has been proposed: d=(P−bb′)/(av)−(ba′)/ad=(P−bb′)/(av)−(ba′)/a, being a, a′, b and b′ constant values for each alloy and under the employed experimental conditions. The values of these coefficients have been estimated from the fitting to the experimental depth values of 5083 and 6082 butt welds generated under conduction regime.
This paper reports the improvement of a high-efficiency mass-production process for large area multi-crystalline silicon (mc-Si) solar cells. A new cell structure and optimization of fabrication process has achieved 18.6% efficiency with mc-Si wafer in practical size of 15 cm × 15 cm, independently confirmed by National Institute of Advanced Industrial Science and Technology (AIST). Main fabrication process of the development are as follows; (1) novel texturization method by combination of laser patterning and wet chemical etching, (2) optimization for screen printing metallization process of firing profile condition, front and back metal electrode material, (3) reduction shading losses of front grid electrode by using modified screen and front metal electrode.
The formation of the front contact is one major topic for solar cell industry. In addition, for multicrystalline silicon (mc Si) there has been no breakthrough in establishing an efficient and cost effective surface texturisation technology for considerable front surface reflection reduction yet. This paper gives an overview on the integration of the V-texturisation into industrial solar cell processes applying the following economical attractive metallisation methods: screen-printing, roller-printing and buried contact formation. For these metallisation methods cell efficiencies of 16.0–16.3% on BAYSIX mc Si (area 100–156 cm2) have been reached with 4–7% rel. efficiency increase as compared to untextured reference cells. In addition solar cell simulations based on realistic assumptions for the contact geometry and electrical performance are given. Finally, a comparison between solar cell concepts with homogeneous and selective emitter including a mechanical V-texture is presented.
Tensile properties and formability are important parameters in many applications. Being a lightweight material, aluminum is increasingly employed in the fabrication of automotive body panels. This study performs butt welding without filler metal on two frequently used automotive body panel aluminum alloys, 5754-O and 6022-T4E29. Welding is conducted using a Nd-YAG laser with a rectangular wave form having various pulse levels (ΔP) but a constant mean power of 1.5 kW. For both alloys, the results indicate that the travel speed required to achieve a successful butt joint increases as ΔP decreases. For a constant pulse level, the travel speed required for the higher Mg content 5754-O alloy (2.9 wt.% Mg) is approximately 2.5 times that of the lower Mg content 6022-T4E29 alloy (0.61 wt.% Mg). Additionally, it is shown that the tensile strength, percentage elongation and formability of both alloy weldments increase with decreasing ΔP level. In the 5754-O alloy, these trends are attributed primarily to the occurrence of magnesium evaporation during the welding process, microstructure refining, and porosity reduction in the resultant welds. However, for 6022-T4E29, the evaporation of Mg is not significant, and consequently, the variation in porosity is not great. These results are caused by a lower Mg content in the base metal. Therefore, the enhancement of the mechanical properties observed in the weldments is a result of a refinement of the weld microstructure.