Pulsed Laser Welding Research Articles

Industrial picosecond pulse laser welding of stainless-steel to quartz for optical applications

We report on the development of a robust picosecond laser welding process for the industrially relevant material combination of quartz and stainless steel. The process requires high numerical aperture focusing of a 6 ps 1030 nm laser through the transparent quartz onto the interface between the two materials. It is found that increased mechanical pressure applied during welding increases reliability and weld performance and with the correct choice of welding parameters parts will survive ISO standard thermal cycling and vibration testing demonstrating the suitability of the process for industrial application.

Study on molten pool flow and hot cracking of narrow gap laser welding of 316LN stainless steel for fusion reactor

In this paper, narrow-gap laser welding (NGLW) of 316LN stainless steel was studied. The results indicated that continuous laser welding with filler wire (CLWFW) and pulsed laser welding with filler wire (PLWFW) can obtain good weld formation under the transition of the wire bridge, and when the pulsed laser was a trapezoidal wave, the hot cracks of the filling layer can be greatly inhibited. The intermittent output of the pulsed laser reduced the temperature gradient of the molten pool and enhanced the morphology of the caudal region of the molten pool. Meanwhile, timely liquid backfilling effectively relieved the stress concentration of the weld, thus inhibiting the generation of hot cracks. Besides, the intermittent pulse energy input had a stirring effect on the molten pool, which disturbed the growth direction of the dendrite grain and refined the grain; consequently, the impurity elements were fully diffused, and the distribution of elements in the weld center area was more uniform.

Increased tensile strength induced by the precipitation of nanocrystals for welding joints of Zr-based amorphous alloys

Zr-based amorphous alloys have attracted intensive attention for applications because of their excellent mechanical property. However, the welding process is inevitable for some special cases, such as the obtain of large size structure parts. It is significant to clarify the influence of introduced welding joints on mechanical properties in Zr-based amorphous alloys. Herein, the increased tensile strength of welding joints in Zr-based amorphous alloys is demonstrated by choosing a suitable initial temperature of Cu cooling fixtures for pulsed laser welding. It is found that an optimized tensile strength is observed when the initial temperature is −20 °C. With the decrease of the initial temperature from 10 to −30 °C, the tensile strength shows a trend of first increasing and then decreasing. Combined with the characterization of microstructures, it can be concluded that the increased tensile strength results from the precipitation of nanocrystals in the heat affected zone. Thus, our results provide a method to improve the mechanical property by controlling the microstructures of the heat affected zone in welding joints of Zr-based amorphous alloys.

Ultrashort pulse laser welding of alumina ceramic and titanium

The direct welding of alumina ceramic and titanium using ultrashort pulse laser was successfully achieved for the first time. Benefitting from the extremely high peak power of ultrashort pulse laser, ceramics can be melted at a very low laser power. The emerging welding method was conducted at room-temperature without the need for preheating. Within the joint, a combination of Ti and Al elements was observed. A newly formed TiO2 phase was identified at the Al2O3/welding seam interface. Under the optimal welding parameters (welding speed: 0.8mm/s, laser power: 19.52W), the joint achieved a maximum four-point bending strength of approximately 134.9MPa. This study proposed a new methodology for butt welding of ceramics and metals and shows a much higher efficiency than the commonly used ceramic-metal joining approaches such as brazing and diffusion bonding.

Improvement in weld quality of Al and Cu joints using dual-beam laser welding

The high weld quality of dissimilar aluminum (Al)/copper (Cu) joint is essential to improve the reliability of connecting components in secondary batteries. This study was aimed at enhancing the weld quality of dissimilar AlCu joints to connect tab-to-busbar in secondary batteries. AA1050 and Ni-coated Cu (C1100) sheets were lap-welded using dual-beam laser welding with a continuous-wave (CW) laser for welding and a pulsed laser for preheating. Consequently, the weld quality was investigated by characterizing the morphology, microstructure, and mechanical and electrical properties of the joints. For comparison of the weld quality, single-beam welding was also performed. Soundly welded joints were achieved using a dual-beam at a CW laser power range of 1000–1400 W for fixed pulsed laser power and welding speed of 100 W and 80 mm/s, respectively. Microstructural analysis of the weld indicated that the upper weld metal (WM) comprised α-Al and AlCu eutectic phases, whereas the lower WM exhibited mixed morphology of different phases including Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Further, the electrical resistance was linearly correlated with weld penetration depth, exhibiting a minimum of 352.3 μΩ against a penetration depth of 341.7 μm. In addition, The Vickers microhardness and lap shear tensile testing of soundly welded sample (A4) exhibited an average hardness value of 921.7 HV in the lower WM, and the average tensile load for the welded sample was 247.4 N. This study provides valuable insights for improving the weld quality of reliable AlCu dissimilar joints for connecting tab-to-busbar in secondary batteries.

Effect of preheating temperature on the microscopic structure and mechanical performance of pulsed laser welding in sheet AZ31 alloy

To achieve high quality welding of an AZ31 magnesium alloy sheet, butt experiments are conducted using an Nd:YAG pulsed laser welder to weld the AZ31 magnesium alloy (1 mm). The influence of preheating temperature on the microscopic structure and mechanical performance of AZ31 magnesium alloy pulsed laser welding is studied. Experimental results show that with the rising of preheating temperature, the grain size of an equiaxed crystal in the weld center and columnar crystal at the fusion boundary (FB) first decreases and then increases and reaches the minimum values of 18.89 ± 0.45 and 32.09 ± 1.52 μm, respectively, when preheated at 200 °C. The maximum force and tensile strength increase first and decrease and reach the maximum of 2.32 kN and 193.3 MPa, respectively, when the preheating temperature is 300 °C. Above all, the welds with excellent mechanical performance can be obtained at the preheating temperature of 300 °C.

Optimization and GRA prediction of Al–Cu pulsed laser welding process based on RSM

In this paper, the process parameters of pulsed laser welding of Al–Cu are studied using response surface methodology (RSM) and grey relation analysis (GRA) to propose optimal directions for lap-shear strength of the joints. A single-factor experiment was conducted to find the suitable process parameter windows. The RSM models were established and analyzed with laser power, welding speed, pulse width, and frequency as inputs and joint lap shear, interfacial weld width, and weld-penetration-depth as outputs. With the use of GRA of interfacial weld width and weld penetration depth with the lap-shear force of joints, the improved direction for the lap-shear force of joints can be proposed.

Enhanced structural, optical and electrical properties of polycrystalline WO3 thin films achieved by aluminum nanosheets coating

Herein the effects of aluminum nanosheets on the structural, morphological, optical and electrical properties of tungsten oxide thin films are reported. Polycrystalline phase of the thermally evaporated WO3 was achieved by the pulsed laser welding technique. The polycrystalline films are then coated with Al nanosheets of thicknesses of 100 nm and 150 nm by the ion coating technique. It is observed that Al induces the domination of the hexagonal structure of WO3 over the tetragonal. Associated with the enhanced crystallinity the light absorption in the films increased by more than 60% and the energy band gap narrowed significantly. Namely the energy band gap of the as grown WO3 decreased from 3.15 eV to 2.85 eV and 2.59 eV as the Al layer thickness increased from 100 to 150 nm, respectively. It is also observed that crystalline films of WO3 exhibited lower electrical resistivity compared to films fabricated by other techniques. The temperature dependent electrical resistivity measurement was carried out in the temperature range of 310–420 K. It showed room temperature values of 2.5 ( Ω cm), 2.2 ( Ω cm) and 1.9 ( Ω cm) and impurity levels centered at 0.25 eV, 0.34 eV and 0.16 eV for uncoated and films coated with Al nanosheets of thicknesses of 100 nm and 150 nm, respectively. The enhanced crystallinity that is accompanied with narrower energy band gap and lower electrical resistivity values make crystalline WO3 films promising for optoelectronic applications.

Effect of nanosecond pulse laser power on welding interface and mechanical properties of AZ31B Mg/6061 Al

AZ31B magnesium alloy and 6061 aluminum alloy of 0.2 mm thickness were joined by nanosecond pulsed laser welding technology, and the effects of nanosecond pulsed laser power on the formation of weld seam, interface microstructure and mechanical properties were investigated, and numerical simulation of the temperature field during the welding process was carried out. The results show that when the laser power is 50 W, more defects such as cracks, pores and sags appeared in the joints due to the high heat input, and these defects resulted in a smaller effective joint area between the metals, which is very unfavorable to the strength of the joints. As the laser power decreases, at a laser power of 25 W, fewer defects are exhibited and the effective joint area becomes larger. As the laser power continues to decrease, the low heat input makes metal melting and joining very difficult. At low laser power, the Mg element intrudes backwards into the aluminum, causing the joint boundary interface to take on a reverse “V” shape. According to the results of the tensile shear experiments, the maximum tensile force of the joint was the highest at a laser power of 25 W, which reached 76.5 N. In addition, it was observed that the effective joint area, the number of oxides and their inclusions, and the degree of angular deformation had a very important effect on the mechanical properties of the joints. The results of temperature field numerical simulation experiments show that the heat is accumulated from outside to inside during the laser scanning process, and whether the temperature in the center of the molten pool reaches the melting point of the alloy can be used as an important basis for analyzing the degree of welding.

The characteristics and dynamics of fused silica-aluminum alloy welding during mJ-level femtosecond laser

Recent research has focused on the ultrafast laser welding of metal and glass due to its diverse applications in aerospace, medicine, and optical sensing. However, the significant material property differences between metals and glass, along with strict surface requirements, pose challenges to the development of metal-glass welding and limit its industrial utility. Utilizing high-pulse-energy lasers has proven effective in mitigating these challenges. This study comprehensively analyzes a millijoule (mJ)-level femtosecond pulse laser welding technique applied to aluminum alloy and fused silica, with a primary emphasis on understanding the characteristics and mechanism of joint. During the welding process, aluminum and fused silica mutually diffuse, leading to the formation of five distinct zones at the joint's cross-section. Within the aluminum molten pool in rapid cooling, aluminum grains undergo continuous growth along a temperature gradient and then transform into smaller epitaxial grains with altered grain orientations and HAGBs. An amorphous Al2O3 phase coexists with aluminum, forming a lamellar structure. Besides, silicon nanoparticles and transitional γ-Al2O3 precipitate near the center of the weld. This study examines the underlying causes of these phenomena and provides a detailed discussion of the associated strengthening mechanisms, ultimately resulting in a maximum shear strength of 8.94 MPa.

Fast crystallization of InSe thin films via pulsed laser welding technique and effect of crystallinity on the optical and dielectric properties

In the current study the crystalline phase of indium selenide thin films which were grown by the thermal evaporation technique is achieved via pulsed laser welding technique (PLW) in a second. The films crystallinity is achieved under various welding conditions including the pulse width ( PW ), repetition frequency ( fr ) and pulse diameter ( d ). The optimum parameters for obtaining well crystalline phase are PW=1.0 ms, fr=10 Hz and d= 1.0 mm. PLW induced crystallinity showed preferred structure relating to monoclinic phase of InSe. Compositionally while amorphous films exhibited In2Se3 chemical structure, crystalline ones preferred InSe phase. Associated with this type of crystallinity, direct and indirect energy band gap values of 2.32 eV and 3.12 eV are determined. The crystalline films showed lower dielectric constant value accompanied with higher optical conductivity and higher terahertz cutoff frequency in the infrared range of light. In addition the dielectric dispersion spectra were treated using Drude–Lorentz model to read the optical conductivity parameters for the PLW assisted crystalline InSe terahertz resonators. The treatment showed that the crystallinity of the films resulted in improved free carrier density, longer relaxation times at femtosecond level, larger plasmon frequencies and higher drift mobility values. These features together with the response of terahertz cutoff frequency to IR excitations make crystalline InSe thin films promising for optoelectronic and terahertz technology applications.

Optical strain measurements during pulsed laser beam welding to improve the understanding of hot crack formation of EN AW-6082 aluminum alloy

E-mobility turned in the last years to be an emerging market and one solution to fossil fuel free mobility for the future. E-mobility requires, compared to fossil-fueled mobility concepts, a huge amount of welding tasks, which have to guarantee different functionality, as for example high strength, ductility, but also low resistivity and tightness. Last is especially for housing or cases of aluminum in automotive challenging, as pores and cracks can occur. Pulsed laser welding presents, due to the adaptable heat input and the temporal modification of stress state and solidification conditions advantages for this type of applications. EN AW-6xxx group of aluminum alloys is mainly used for such components due to their favorable mechanical properties. However, these alloys are susceptible to hot cracking during solidification from the molten phase. This article aims to present a methodology for demonstrating the resulting strain during pulsed laser beam welding of hot crack susceptible aluminum alloys. It will highlight the influence of factors such as pulse shape, shielding gas, and flow rate on strain and strain rate.

Monitoring laser weld penetration status from the optical signal

Spectrometers have demonstrated their value in laser welding by facilitating the comprehension of welding dynamics and the identification of defects. However, the complex interaction between the laser beam and the material being welded makes it difficult for spectrometers to accurately capture the depth and extent of weld penetration, predominantly because plasma formation during welding interferes. This study presents an innovative approach that integrates laser technology, spectrometers, and advanced data analysis methods to classify and characterize various penetration types in pulse laser welding procedures, with notable computational efficiency. The research entailed the execution of an experiment on a boron steel plate, wherein peak power (1000-1200 kW), pulse duration (2-4 ms), and pulse repetition rate (25-50 Hz) were systematically varied to achieve diverse penetration conditions. Two categories of joints were identified based on their depth of penetration through careful analysis of the collected data. The investigation demonstrated a positive correlation between the depth of weld penetration and the increment of laser energy, with peak power ranging from 1000 kW to 1200 kW. Consequently, an elevation in light intensity was observed related to deeper weld penetration. The information is essential for understanding the relationship between laser energy and weld penetration, highlighting the importance of controlling laser parameters to achieve desired welding results. The spectrums were analyzed using Principal Component Analysis (PCA) to distinguish between different welding conditions. Overlap was observed between data from different weld conditions due to limitations imposed by the restricted dataset. Expanding the sample size can rectify this limitation and improve the accuracy and dependability of analytical outcomes. This study’s results provide valuable insights into optimizing welding parameters and improving understanding of the welding process, specifically in Tailor Weld Blanks. The findings offer potential for improving welding quality and strengthening lightweight components in high-performance industries like aerospace and automotive engineering.

Formation, Enhanced Crystallization, Optical Absorption and Electrical Conduction in Copper Indium Selenide Thin Films Prepared via Pulse Laser Welding Technique

AbstractIn this study, thin films of CuInSe2 (CIS) are expeditiously fabricated within 1 s utilizing the pulsed laser welding (PLW) technique. Preceding the PLW process, thin films of InSe (500 nm) are coated with Cu nanosheets of 60 and 120 nm thicknesses using vacuum coating systems. The optimal PLW parameters leading to the formation of CIS films include a pulse width of 1.0 ms, a spot diameter of 2.0 mm, and a repetition frequency of 10 Hz. The resulting CIS films exhibited a well‐crystalline cubic structure with lattice parameters of 5.265 Å. Surface morphology analyses revealed the preferential formation of porous films with varying stoichiometry, a characteristic that can be manipulated by adjusting laser welding parameters. The energy band gap and room temperature electrical conductivity display values of 1.80 eV and 2.06 × 10−5 (Ωcm)−1, respectively. Cu‐rich samples exhibit a wider energy band gap of 1.94 eV and lower electrical conductivity values of 4.78 × 10−7 (Ωcm)−1. The CIS film demonstrates n‐type conductivity attributed to the formation of donor levels centered at 0.24 and 0.10 eV. This study presents an ultrafast method for fabricating CIS films with physical properties compatible with those produced using traditional methods.

Statistical analysis of plasma thermodynamic behavior based on laser deep penetration welding of TC4 titanium alloy

The laser-induced plasma is an important characteristic that affects the welding process and weld quality. The plasma plume erupting velocity and temperature are the two critical parameters of plasma thermodynamic behavior. In this paper, a kind of passive dual-probe device was proposed to measure the erupting velocity of the plasma plume, and the feasibility of the method was demonstrated. The temperature distribution of the plasma plume was also investigated. The experimental results showed that for the reason of the state of the keyhole was different, the MPV at the beginning of the laser pulse period increased from 14 m/s to 26 m/s with the peak power increased from 1980 W to 2520 and from 4 m/s to 25 m/s with the peak power increased from 1200 W to 1500 in the pulse laser welding process, while the MPV decreased from 20 m/s to 11 m/s with the laser power increase from 1200 W to 1500 W in the continuous laser welding process. The MPT decreased with the increase of height in pulse laser welding process; but in the continuous laser welding process, the plasma plume was heated by absorbing the laser energy and a hot core occurred in the plasma plume, the MPT first increased and then decreased with the increase of probe height.

The role of asymmetric metal flow on weld formation and solidification characteristics during pulsed laser butt welding with assembly tolerance

In comparison to other laser-assisted welding techniques, the pulsed laser welding process (PLBW) provides cost-effectiveness and ease of operation while effectively connecting butt-assembled thin plates with manufacturing tolerances (both air gap and edge misalignment). A combination of numerical simulations and experimental studies was conducted to analyze the forming mechanism and solidification behavior of the weld. In this paper, a transient three-dimensional heat-flow-metallurgical model has been established for a PLBW process of mild steel plates with a thickness of 1.8 mm. The predicted weld pool profiles were consistent with the experimental findings. The finding suggested the molten metal, driven by surface tension and recoil pressure, successively generated liquid bridges on the rear and front sides of the pool. The two sheets were joined as the molten metal gradually solidified. The energy absorptivity was highly correlated with the weld pool and keyhole dynamics, and the laser energy absorbed by the metal was mainly transferred in the form of thermal convection. The kinematic features of the melt were observed by the liquid phase mass transfer rate and surface fluctuations. According to the Fourier analysis results, the molten pool oscillated at the characteristic frequency of the laser pulse frequency. The spatial and temporal distributions of solidification parameters aided in analyzing the solidification features within the pool. The asymmetric flow had a greater influence on the temperature gradient. These findings addressed the roles of PLBW on fluid flow, heat behaviors, and solidification parameters of welds with assembly tolerances, as well as the reasons for improved weld formation.

Effect of preheating temperature on the defects in pulsed laser welding of sheet AZ31 magnesium alloy

To suppress the welding defects of thin sheet magnesium alloy by pulsed laser welding, AC-300 W pulsed laser welder is used to weld 1 mm magnesium alloy at different preheating temperatures, and the effect of preheating temperature on solidification cracks, pore and undercut are studied. Preheating temperature is set at 25 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃, 300 ℃ and 350 ℃. Results show that preheating increases the peak temperature (1494.14 ℃ to 1785.86 ℃) and reduces the cooling rate (14489.33 ℃/s to 14282.11 ℃/s) of the molten pool, thereby reducing welding defect sensitivity. When preheated at 200 ℃, the solidification cracks and pores disappear, and the undercut depth reaches the minimum value of 0.04 mm.

Effect of process parameters on surface formation in laser welding of Al2O3 ceramic

The attainment of formability in ceramic welding presents an imposing quandary within the realm of the manufacturing industry. In this article, the laser welding of Al2O3 ceramics was carried out to compare and analyze the influence of laser power, welding speed, laser duty cycle, and other process parameters on the macroscopic morphology of the weld, weld cracking rate, and welded joint properties. The results show that Al2O3 ceramic welds have a greater tendency to cracking and that the laser power should be matched to the appropriate welding speed. When heat input increases, the weld cracking rate decreases and then increases. Ceramic welded joints with a weld cracking rate of less than 30 % and a bending strength of more than 4 MPa can be obtained when the heat input range is 17–20.5 J/mm for continuous laser welding or 20.5–24 J/mm for pulsed laser welding. In addition, under high heat input conditions, pulsed laser welding reduces the tendency for weld cracking compared to continuous laser.

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Study on pulsed wave mode laser welding of Nb-Zr-C alloy and many-objective optimization using meta-heuristic techniques

Investigation of Single-Pulse Laser Welding of Dissimilar Metal Combination of Thin SUS303 SS and Cu

The present study investigated the dissimilar metal combination of SUS303 stainless steel (SS) and pure copper C19210 by utilizing a fiber pulse laser to perform lap welding. The weld quality was evaluated through metallurgical and mechanical examinations, including scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive spectroscopy (EDS), as well as tensile and shear tests. The cross-section of the weld joints was observed to examine the penetration inside the molten zone of the pulse laser welding. The incomplete weld penetration depth was confirmed by analyzing the molten pool geometry, which indicated that the penetration depth was proportional to the pulse heat energy input. EDS analysis demonstrated that interdiffusion and dissolution of Cu and SS occurred inside the weld pool, although only a limited amount of Cu was melted. Microhardness (MH) exploration revealed the hardness of the molten zone was lower than that of the heat-affected zone (HAZ) on the SS side, while the hardness on the Cu side, closer to the molten zone, was higher. The results of the tensile test indicated that the fracture occurred in the HAZ on the Cu side, displaying a dimpled fracture mode characteristic of ductile fracture.