Laser Welding Research Articles

Microstructure formation mechanism and mechanical properties of super-thickness TC11 titanium alloy joint by electron beam welding and laser additive manufacturing hybrid connection technology

Advanced connection technology for extra-large/super-thickness titanium wrought components is urgent demand in aerospace manufacturing industries. For achieving high-performance titanium alloy super-thickness joint with a high connecting efficiency, a novelty concept of hybrid connection technology with electron-beam welding and subsequent laser additive connection is proposed. A super-thickness (200 mm) TC11 titanium alloy joint has been successfully prepared, and microstructure, tensile properties and fracture behavior of different regions in which are investigated. The results suggest that in stress-relieve heat treatment (SRT) condition, deformation and fracture of the joint are prone to occur in its low-strength wrought base material zone; after double annealing heat treatment (DAT), lamellar α phases in different zones of the joint become similar, associating with a higher fraction of fine secondary α phases in wrought base material zone. Therefore, the tensile properties of the joint are comparable to wrought properties. Although strength in different zones of hybrid connection joint is similar, ductility is not uniform and apparently lower in middle fusion zone due to grain heterogeneity. Overall, these findings indicate that hybrid connection can be one potential technology for fabricating high performance super-thickness titanium alloy joint with a high connection efficiency in engineering application fields.

Corrosion behavior of combination of laser beam welded UNS S32304 + SS304L in 3.5% NaCl solution

This study investigates the corrosion behavior of laser beam-welded UNS S32304 and SS304L in 3.5% NaCl solutions, focusing on the effects of temperature. The primary objective is to enhance the understanding of corrosion resistance in welded materials and inspire advancements in corrosion mitigation strategies. The methodology involves assessing corrosion resistance under varying temperatures and comparing the performance of laser beam welding (LBW) with that of the base metals. Scanning electron microscopy analysis reveals effective passivation, while quantitative analysis indicates differences in chloride ion coverage between the weld metal and base metals. Tafel plots and electrochemical impedance spectroscopy demonstrate enhanced corrosion potential and improved barrier properties for the weld metal. Results indicate a marginal reduction in corrosion resistance at 50 °C for both base metals. LBW metals corrosion resistance demonstrates superior performance, with only 5% reduction in breakdown potential compared to 10% in base metals. Compared to the base metal, it exhibits a substantial reduction in corrosion rate, ranging from 60 to 75%. This supports enhanced corrosion resistance and material stability. Additionally, similar results are observed after the analysis with scanning electron microscopy images, reinforcing the efficacy of LBW in improving corrosion resistance of LBW UNS S32304 and SS304L. These findings underscore the potential of LBW for applications requiring robust corrosion performance. By contributing to the understanding of the corrosion behavior of laser beam-welded materials, this study addresses a critical research gap in material science and corrosion engineering. Future research may explore long-term durability and corrosion resistance under diverse environmental conditions to further elucidate the mechanisms driving the observed differences in corrosion behavior.

Analysis of the dynamic behaviors of molten pool and keyhole for the oscillating laser welding of dissimilar materials stake welded T-joints with a gap

The dynamic behaviors of molten pool and keyhole have the significant effects on weld quality and joint performance. To investigate the circular shaped oscillating laser welding (OLW) of dissimilar materials stake welded T-joints with a gap between the face plate (FP) and web plate (WP), a dynamic model of molten pool and keyhole for the OLW of dissimilar materials stake welded T-joints with a gap is developed and the dynamic behaviors of molten pool and keyhole during the weld formation process are analyzed and discussed in detail. Based on the calculated results, it is found that the laser beam mainly radiates on the front wall of keyhole and the hump is formed on the rear wall of keyhole relative to the moving direction of laser beam at the FP welding stage. At the gap penetration stage, the keyhole opening at the molten pool bottom of FP shows the trumpet-shaped characteristic and the molten pool is divided into the upper and lower parts by the gap. The formed gas cavity is separated and fused with the keyhole several times at the WP welding stage. The gap around the gas cavity is disappeared after the reintegration of the upper and lower parts of molten pool. The depth of molten pool shows the periodic fluctuation characteristic with time and the fluctuation period is nearly the same as the oscillation period of laser beam during the OLW process.

A Low-Cost Laser Welding Monitoring Framework Based on Depth-Wise Separable Convolution with Photoelectric Signals

A Low-Cost Laser Welding Monitoring Framework Based on Depth-Wise Separable Convolution with Photoelectric Signals

Active control effect of shielding gas flow on high-power fiber laser welding plume

Plume are common physical phenomena in fiber laser keyhole welding and have serious negative effects on the welding process. Based on this, this paper explores the regulation law of conventional shielding gas flow on plume. The results show that the shielding gas has a very significant effect on the suppression of the slender part of the plume, and the greater the gas flow rate, the better the plume removal effect. The addition of the shielding gas makes the welding process more stable, the molten pool flows stably, and the frequency of spatter eruption is reduced. Under the experimental conditions, the optimal shielding gas flow rate is around 15 l/min, and the penetration depth and width are increased by about 10% and decreased by about 22%, respectively, compared with that without adding the shielding gas. Based on the gas flow simulation, the gas flow pressure (about 132 Pa) generated by an appropriate amount of shielding gas (about 15 l/min) can press the liquid column and spatter near the keyhole mouth into the molten pool to avoid the spatter eruption. Excessive shielding gas flow will interfere with the flow of the molten pool excessively, and the weld surface will show a serious undercut phenomenon.

Dissimilar Laser Welding of Plastic to Stainless Steel with a Flat-Top Heat Source: Numerical Simulation and Experimental Investigation

Dissimilar Laser Welding of Plastic to Stainless Steel with a Flat-Top Heat Source: Numerical Simulation and Experimental Investigation

Multi- objective modeling and optimization of dissimilar laser welding by integrating an artificial intelligence predictive model with NSGA-II algorithm

This study presents a pioneering approach in laser welding of two dissimilar materials by integrating an Artificial Intelligence (AI)-based on predictive model with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) for optimizing key performance characteristics of Nickel-based alloy and duplex 2205 stainless steel. Focusing on four primary input variables including laser power, welding speed, focal distance and deviation, the research aims to predict and optimize the responses including temperature field adjacent to the melt pool, penetration depth, and tensile strength of the joint according to the experimental results. The developed AI model first accurately forecasts these characteristics based on the inputs. This predictive accuracy is critical in defining the optimal target values. Considering the multidimensional nature of the problem, where enhancing one characteristic could compromise another, the study employs a Multi-Objective Optimization (MOO) strategy. This is where the innovative integration with NSGA-II becomes pivotal. Renowned for its efficiency in navigating multiple, potentially conflicting objectives, NSGA-II assists in achieving a balanced optimization of all target parameters. This method is adept at considering the complex interdependencies among various characteristics. The novelty of this work lies in its unique combination of AI for prediction and MOO for optimization and it is for the first time that machine learning is applied on this kind of alloys with four features and four targets.

Study on the keyhole oscillation mechanism of laser welding based on electro-mechano-acoustical analogy theory

The acoustic emission phenomena generated by the laser welding process are closely related to the keyhole's forced oscillation and the dynamic pressure balance at the keyhole bottom. In this study, we constructed the mechanical equation of keyhole bottom pressure balance and used the “electro-mechano-acoustical” analogy theory to convert it into an acoustic equation, the acoustic resonant frequency as well as the magnification amplification factor of the keyhole oscillation in different penetration states were derived. A monitoring platform combining acoustic sensor and high-speed photography was established to obtain acoustic emission signals and lateral keyhole images. The acoustic and image features extracted from the monitoring data validated the derived formulas. Additionally, the acoustic phenomena of different frequency-energy components were explained according to the derived formulas in turn. The results demonstrated that the derived theory is compatible with experimental comparisons, showcasing its great interpretability and applicability. The introduced analogy theory effectively establishes a bridge between keyhole forced pressure and acoustic emission vibration, aiding in the understanding of keyhole oscillation characteristics. A novel model of keyhole oscillation was proposed and verified using process monitoring data in this study, which provides a new approach for the investigation of keyhole dynamic.

Study of the effect of laser beam welding on joint of Nimonic 80A superalloy: an experimental approach

Study of the effect of laser beam welding on joint of Nimonic 80A superalloy: an experimental approach

Study on pore behavior of laser welding process between steel and CFRP based on numerical simulation

In order to understand the pore behavior during laser welding of metal and polymer, the laser welding of steel and carbon fiber reinforced plastics (CFRP) was studied. A three-dimensional transient model of multi-physical field couple with heat, flow and force was constructed to simulate the temperature distribution, fluid flow, stress change and solidification under the thermal decomposition of CFRP based on the experiments. The formation, function and evolution mechanism of pores in welded joints were discussed, and the relationship between heat input and pore morphology at the interface was clarified. The results show that the model error is lower than 9 %, and the model is reliable. In laser welding process, bubbles generate, expand and fuse in the center of CFRP molten pool, which changes the local flow velocity and direction, but most of the fluid still flows to the molten pool edge under the action of temperature gradient, and forms pores of stable size with the cooling process. When the heat input is high, the large pores are formed at the interface due to the violent thermal decomposition of CFRP and big stress difference. When the heat input is low, there is still a large stress gradient in the center of the interface, and it is difficult for the insufficiently melted polymer to provide sufficient resistance to deformation, resulting in obvious pore phenomenon in the center of the interface.

A VMD-BP Model to Predict Laser Welding Keyhole-Induced Pore Defect in Al Butt-Lap Joint.

The detection of keyhole-induced pore positions is a critical procedure for assessing laser welding quality. Considering the detection error due to pore migration and noise interference, this research proposes a regional prediction model based on the time-frequency-domain features of the laser plume. The original plume signal was separated into several signal segments to construct the morphological sequences. To suppress the mode mixing caused by environmental noise, variational modal decomposition (VMD) was utilized to process the signals. The time-frequency features extracted from the decomposed signals were acquired as the input of a backpropagation (BP) neural network to predict the pore locations. To reduce the prediction error caused by pore migration, the effect of the length of the signal segments on the prediction accuracy was investigated. The results show that the optimal signal segment length was 0.4 mm, with an accuracy of 97.77%. The 0.2 mm signal segments failed to eliminate the negative effects of pore migration. The signal segments over 0.4 mm resulted in prediction errors of small and dense pores. This work provides more guidance for optimizing the feature extraction of welding signals to improve the accuracy of welding defect identification.

Effect of Quenching and Aging on the Microstructure and Mechanical Properties of Welded Joints Obtained by Laser Welding of Titanium and Aluminum Alloys

Effect of Quenching and Aging on the Microstructure and Mechanical Properties of Welded Joints Obtained by Laser Welding of Titanium and Aluminum Alloys

Numerical and experimental investigation of the effect of heat input on weld bead geometry and stresses in laser welding

Abstract Nowadays, laser welding is a powerful joining method. Thanks to the advantages it has, its usage area is increasing day by day. However, getting the desired result from the laser welding process is possible with the proper welding parameter selections. Otherwise, many problems may be encountered, including significantly incomplete penetration. For this reason, parameter selection has been discussed in many studies in the literature. At this point, validated numerical simulation models are precious. Since these models reduce experiment costs and save time. Especially numerical simulation of the structural steel, which is the one of most used materials, is crucial. In this study, the effects of laser power (LP) and welding speed (WS), which are among the vital parameters of laser welding, on weld width and stress were investigated numerically and statistically. Structural steel was selected as the material, and the Taguchi method was carried out for the simulation case study design. Simufact Welding software was used for simulation studies, and simulations were carried out thermomechanical. Thus, more realistic results were obtained via the thermomechanical method. One of the simulation results was verified through an experimental study. The results were evaluated with signal-to-noise (S/N) ratio and a statistical analysis of variance (ANOVA), and as a result of the study, it was seen that the welding speed was a more effective parameter, the optimal parameter combination was found to be 3500 W for laser power and 40 mm/s for welding speed to get maximum weld width and minimum equivalent stress. In addition, it was observed that correctly created simulation studies may provide very close results to experimental studies.

CFD modeling for predicting imperfections in laser welding and additive manufacturing of aluminum alloys

Aluminum and its alloys are widely used in various applications including e-mobility applications due to their lightweight nature, high corrosion resistance, good electrical conductivity, and excellent processability such as extrusion and forming. However, aluminum and its alloys are difficult to process with a laser beam due to their high thermal conductivity and reflectivity. In this article, the two most used laser processes, i.e., laser welding and laser powder bed fusion (LPBF) additive manufacturing, for processing of aluminum have been studied. There are many common laser-material interaction mechanisms and challenges between the two processes. Deep keyhole mode is a preferred method for welding due to improved productivity, while a heat conduction mode is preferred in LPBF aiming for zero-defect parts. In LPBF, the processing maps are highly desirable to be constructed, which shows the transition zone. Presented numerical modeling provides a more in-depth understanding of porosity formation, and different laser beam movement paths have been tested including circular oscillation paths. High accuracy processing maps can be constructed for LPBF that allows us to minimize tedious and time-consuming experiments. As a result, a modeling framework is a highly viable option for the cost-efficient optimization of process parameters.

A Study on Laser Welding of Dissimilar Materials between Aluminum and Copper (Ⅱ) - Development of Laser Welding Quality Verification Technique -

The quality management of laser welding is crucial for EV battery manufacturing as it directly affects vehicle safety. However, there is currently no test standard to evaluate the quality of laser-welded structures. Visual inspection and tensile testing have been used to examine the quality of lap joint laser welding. However, it is dangerous to determine the optimal welding parameters only by tensile strength. The aim of this study was to determine the optimal laser welding parameters by conducting tests for various load directions, such as peel, moment, and low-cycle fatigue tests. As a results, in the case of Al/Cu welding that is highly brittle, the peel test demonstrated greater discrimination than the tensile test. In contrast, the moment test was more effective at determining the strength of the local interface joints. Lastly, the fatigue test yielded similar outcomes to the tensile test. It is challenging to completely replace the tensile test results and utilize them independently. Hence, it is recommended to utilize them exclusively as sub-tests to establish the ideal laser welding conditions.

Finite Element Modeling of Ring and Gaussian Dual Laser Heat Sources for Aluminum Butt Welding

Aluminum alloys have been used extensively for automotive industries for the structural applications with their high specific strength and corrosion resistance. In order to use aluminum alloys for automotive components, laser welding has been used due to the advantage of being capable to weld thick products due to its deep penetration depth. In this regard, a dual laser heat source combining an outer ring laser beam with a centrally focused Gaussian laser beam was proposed to compensate for insufficient melting caused by laser reflection of aluminum alloy. The purpose of this study is to develop a simulation model that can consider heat input from the dual laser beams individually, for analyzing melting and heat distribution behavior during the laser welding. Two different heat source models were proposed. One model used 3D Gaussian distribution of heat input for the centrally focused laser while the other model utilized Gaussian cylinder heat input. The proposed heat input models were implemented by finite element analyses, and the results were compared with aluminum butt welding experiments. It was shown that Gaussian cylinder heat input for the centrally focused laser beam reproduced much better the experimentally observed melting behavior in comparison to the 3D Gaussian distribution.

Modeling and validation of hydrogen porosity formation in aluminum laser welding

Laser welding is used to weld aluminum alloy 1100 for battery cell manufacturing in the automotive industry. However, these welds can have porosity that can decrease their performance in the battery packs. One type of porosity is gas porosity, commonly understood to be due to hydrogen entrapment in the weld during solidification. Hydrogen is dissolved in the molten aluminum at elevated temperatures during laser heating and can be entrapped in the weld pool upon solidification. When welding anodized aluminum, the amount of hydrogen porosity is increased because the anodized oxide layer is broken up and the broken-up oxide can act as heterogeneous nucleation sites for hydrogen pores. A cellular automaton model has been developed to predict the nucleation and growth of hydrogen porosity during laser welding. This model has been validated with microstructure analysis, LECO® hydrogen analysis, and X-ray micro-computed tomography. This model can be used by welding engineers to reduce porosity and control weld quality during laser welding of aluminum alloys.

Mechanical response and microstructural evolution of a composite joint fabricated by green laser dissimilar welding of VCoNi medium entropy alloy and 17-4PH stainless steel

In engineering structures, the application of advanced alloys, such as the VCoNi medium-entropy alloy (VCoNi-MEA), with remarkable tensile strength (> 1 GPa) and superior ductility necessitates the employment of dissimilar joints. This study pioneers the dissimilar joining of VCoNi-MEA and 17–4 precipitation hardening stainless steel (17–4PH STS) using state-of-the-art green laser beam welding (LBW). To evaluate and optimize the experimental parameters, two welding speeds (200 and 300 mm/s) along with post-weld heat treatment (PWHT) were incorporated. High-quality welded joints with a single-phase face-centered cubic (FCC) structure in the fusion zone (FZ), minimal precipitates (< 1.6 %), and no visible cracks were successfully created. The LBW process demonstrated effective low-heat input characteristics, evident from a considerably narrow heat-affected zone (HAZ). Control over FZ width and grain size was achieved, measuring 600 and 112 μm at low welding speed and 250 and 49 μm at high welding speed, respectively, significantly lower than previous studies. A remarkably high yield strength (YS) of ∼620 MPa and ultimate tensile strength (UTS) up to 845 MPa were observed in the as-welded conditions, improving to ∼645 and 875 MPa, respectively, after PWHT. This enhancement in mechanical properties is primarily attributed to lattice friction induced by V addition. PWHT also improved joint ductility, increasing from 3.5 % to 8.6 % (low-speed) and from 6.3 % to 9.2 % (high-speed). The reduction in crystallographic orientation achieved using a higher welding speed and PWHT emerged as a major reason for improved mechanical properties. Slip-based deformation mechanisms dominated across all conditions, featuring crystallographically aligned slip bands. Interactions between existing and additional slip bands formed a dense dislocation network crucial for enhanced elongation after PWHT. Thermodynamic parameters elucidating phase stability in the observed FZs and contributions to superior YS were calculated and comprehensively discussed.

Elevated temperature rusting characteristics of UNS 31254 weldments within the operational confines of fossil fuel-fired plants and municipal waste incinerator surroundings at 700 °C

ABSTRACT This study investigates the air oxidation and rusting traits of fully austenitic alloy 254 stainless steel samples at 700°C after pulse current gas tungsten arc welding (PCGTA) and CO2 laser beam welding (CO2 LBW), with or without molten salt, relevant to coal-fired plants and waste incinerator settings. Among the weldments studied, CO2 laser weldments demonstrate greater resilience to corrosive gas and salt amalgamation, as well as air oxidation, compared to gas tungsten arc weldments, possibly due to thermal disparities and microstructural differences inherent in the welding processes. Protective oxides enhance corrosion resistance in air-oxidised samples, while corrosive compounds like CrS, Cr2K2O7, etc., reduce corrosion resistance and promote spallation in salt-degraded material. A thermogravimetric approach was used to assess rusting effects, alongside microstructural analysis employing optical, Scanning electron microscopy/ Energy dispersive x-ray spectroscopy (SEM/EDS), and X-Ray diffraction analysis (XRD) techniques.

OCT monitoring data processing method of laser deep penetration welding based on HDBSCAN

To address the challenge of low accuracy in the measurement of laser deep penetration welding depth, this study introduces optical coherence tomography (OCT) technology for the direct measurement of this parameter, which is designed to enable real-time measurement and the accurate acquisition of depth information. This study has developed a laser welding depth inspection system that integrates Spectral-Domain OCT (SD-OCT), utilizing 304 stainless steel as the test material for inspecting laser deep penetration welding. A comparative analysis evaluated the impact of Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN), Density-Based Spatial Clustering of Applications with Noise (DBSCAN), and K-means clustering (K-mean) on the clustering of OCT raw data, in addition to the use of percentile filters combined with the exponential moving average method for extracting the depth-of-melt curve. The depth-of-melt curve, obtained via the HDBSCAN algorithm, more accurately reflects the actual depth curve, with an average error remaining below 5%. This error rate is 46% lower than that of DBSCAN and 42% lower than that of K-mean. The results of the experiments with continuously varying process parameters show that a high degree of accuracy can be demonstrated even when the welding process parameters are continuously varied. Experimental results indicate that the combination of the HDBSCAN algorithm with percentile filtering and the exponential moving average method significantly enhances the recognition accuracy of the deep penetration laser welding depth curve. This method provides more precise feature parameters for the real-time detection and identification of defects in deep penetration laser welding, thereby offering strong support for optimizing and controlling the laser welding process.