Laser Welding Of Aluminum Alloys Research Articles

Keyhole stability and surface quality during novel adjustable-ring mode laser (ARM) welding of aluminum alloy

Aims at keyhole instability and poor surface-quality in welding of aluminum alloy, a novel laser technology has been studied on welding of Al 6061. The novel laser beam consists of a ring part and a center part. Different power ratio of ring laser beam to center laser beam and different kind of laser beam welding experiments have been conducted, respectively. The keyhole stability and surface quality were analyzed by using a high-speed camera and a confocal sensor accordingly. Additionally, the energy absorption rate was studied by analyzing the penetration and fusion area of cross-section. Experimental results showed that the ring laser beam provided great stability on the center laser-induced keyhole in high-speed dual-mode ring/center laser welding of aluminum. The stability effects can be improved by increasing the ring power in dual-mode ring/center laser welding of aluminum alloy, and the stabilized effect would contribute to the high-surface quality on welding of aluminum alloy. Furthermore, the combination of ring laser and center laser (Gaussian laser) greatly improved the welding efficiency due to its synergistic effects on process status in the ARM laser welding process. This work provided a basic research to both scientist and engineer on the mechanism of ARM laser welding aluminum alloy.

Quantitative Evaluation of Penetration State in Pulsed Laser Welding of Aluminum Alloys Based on Acoustic‐Wave Time‐Frequency Characteristics and Deep Learning

Quantitative Evaluation of Penetration State in Pulsed Laser Welding of Aluminum Alloys Based on Acoustic‐Wave Time‐Frequency Characteristics and Deep Learning

Cross-attention-based multi-sensing signals fusion for penetration state monitoring during laser welding of aluminum alloy

A precision multi-sensor monitoring strategy is required to meet the challenges posed by increasingly complex products and manufacturing processes during laser welding. In this work, an acoustic sensor and a photoelectric sensor were adopted to collect the signals during the laser welding of aluminum alloy. The dataset was divided into three categories according to the morphologies of the top and back sides. The cross-attention fusion neural network (CAFNet) was proposed to interactively capture photoelectric and acoustic information for effective quality classification without prior time–frequency analysis and feature learning. Its effectiveness and superiority were compared with the five types of deep learning (DL) based methods. It demonstrates that the proposed CAFNet method achieved a mean testing accuracy of 99.73% and a standard deviation of 0.37%, which outperforms other compared models. At the same time, the proposed CAFNet achieved the highest average testing accuracy of 94.34% when utilizing limited and imbalanced data, which suggested that the proposed method has stronger robustness than other methods. This approach is a new paradigm in the monitoring of laser welding and can be exploited to provide feedback in a closed-loop quality control system.

Numerical and experimental study on melt-pool heat transfer and weld characteristics in dual-mode fiber laser welding of aluminum alloy

A dual-mode fiber laser consisting of center and ring beams has attracted significant attention in the laser welding field owing to its ability to stabilize melt pools and reduce defect formation. In this study, a dual-mode fiber laser was adopted for butt welding of an aluminum alloy. Experimental and numerical investigations were conducted to analyze the weld characteristics and heat transfer phenomena during the process. The use of both the center and ring beams produced a funnel-like weld shape because of the low ring beam intensity, resulting only in the melting of the upper part of the workpiece. As the ring beam power increased, the temperature gradient near the solidification front, acting as a driving force for fluid flow, decreased. This contributed to the relatively gentle fluid flow and the smooth bead surface. It was also found that an increase in ring power lowered the cooling rate of the melt zone near the weld edge. Therefore, the average grain size of the weld zone increased with an increase in the ring power. The results of this study provide fundamental insights into the mechanism of dual-mode fiber laser welding.

Online porosity prediction in laser welding of aluminum alloys based on a multi-fidelity deep learning framework

Online porosity prediction in laser welding of aluminum alloys based on a multi-fidelity deep learning framework

Numerical and experimental study of thermal fluid flow and keyhole dynamic in laser welding of aluminum alloy assisted by electromagnetic field

A steady electromagnetic field with high magnetic flux density was designed to improve weld appearance and suppress porosity defect of aluminum alloy laser welded joint. A comprehensive numerical model considering the multiple reflection of laser beam, the magnetohydrodynamics (MHD), and the vapor shear stress on free surface of keyhole was established to reveal the effect of electromagnetic field on thermal fluid flow and keyhole dynamic. A sufficient Lorentz force (∼1.255 × 106 N/m3) is induced when magnetic flux density reaches to 500 mT. The fluids flow downward, forward, and upward in the upper, middle, and lower region are inhibited by the Lorentz force, respectively. Therefore, less heat exists in the bottom and more heat accumulates in the middle edge of the weld pool, leading to the smaller weld depth, larger length at half depth, and disappeared necking when an electromagnetic field is used. Moreover, the impact of vortex on the rear keyhole wall is weakened by the Lorentz force, which decreases the oscillation and breakup of keyhole. This work can help improve the understanding concerning influence of the electromagnetic field on thermal fluid flow behavior in laser welding and provide guidelines for the suppression of porosity and splash defects.

Real-time porosity monitoring during laser welding of aluminum alloys based on keyhole 3D morphology characteristics

This research proposes a real-time porosity monitoring approach for aluminum (Al) alloys laser welding based on keyhole 3D morphology characteristics, realizing the prediction of the local porosity at each position of the weld. Building a multi-sensing signals monitoring platform consisting of a high-speed camera and a coherent optical system, the keyhole 3D morphology is measured. For the keyhole 3D morphological standard deviation (STD) features obtained by the algorithm of sliding window scan, the data processing based on ensemble empirical mode decomposition (EEMD) and principal component analysis (PCA) is adopted to acquire the input of an artificial neural network (ANN). The local porosity is acquired as the output of the ANN by scanning the weld with the sliding window and performing EEMD processing. A feedback mechanism is introduced into the ANN and the genetic algorithm (GA) is utilized to optimize the network parameters to improve the porosity prediction performance of the model. The prediction results show that the constructed optimized ANN can effectively and accurately monitor the porosity, and the generalization ability of the model is strong. In the corresponding relationship between the porosity and each STD feature, it is found that the formation position of the pore lags behind the fluctuation position of the keyhole, which can be explained by molten pool flow.

Study on root hump formation mechanism in full penetration laser welding with backing gas for aluminum alloy

The dynamic behavior of molten pool in full penetration laser welding (FPLW) with backing gas or without backing gas for aluminum alloy was observed. It is found that the backing gas can greatly improve the root hump formation. A transient and multi-phase 3D numerical model considering the metallic vapor ejection process was developed to explain this phenomenon, in which an evaporation and condensation model was established to simulate the production of metallic vapor. Based on the proposed model, the metallic vapor ejection, periodic keyhole variation profiles and molten pool evolution were presented, which indicated that the flow pattern of melt in the molten pool was deeply affected by the vapor ejection pattern. The ejection velocity of vapor is 45–70 m s −1 . The high-speed vapor makes the melt flow (MF) velocity within 1 mm of the keyhole wall change from 5.5 m s −1 to 0.2 m s −1 . The high velocity gradient near the keyhole is the main reason to form an invert cone-shaped sagging under the keyhole and some globular spatters near the keyhole outlet. The surface tension plays an important role to shorten the invert cone-shaped sagging and improves root hump formation. Alumina film formed on the back surface of molten pool can worsen the root hump formation due to the lack of surface tension. • An innovative transient and multi-phase 3D numerical model considered the metallic vapor ejection process was developed to simulate the root hump formation process in full penetration laser welding of aluminum alloy. • The flow pattern of melt in the molten pool evolution was presented in the full penetration laser welding with backing gas. • Proposing that the high-speed metallic vapor results in a significant velocity gradient near the keyhole wall, which is the main reason to form an invert cone-shaped sagging under the keyhole. • Proposing that the surface tension plays an important role to shorten the invert cone-shaped sagging and backing gas is helpful for improving the formation of root hump.

Minimizing defects and controlling the morphology of laser welded aluminum alloys using power modulation-based laser beam oscillation

Due to sensitivity to heat, laser welding of aluminum alloys is always accompanied by serious defects such as porosity and cracks, which restricts their wide application for structures of lightweight applications. Beam oscillating welding can potentially eliminate these defects to a large extent but with shortcoming of low heat utilization rate. For better solution, a Full Domain Power Modulation (FDPM) system was promoted to conduct bead-on-plate welding tests of 6061 aluminum alloys using circular oscillation. The impact of three welding modes (traditional Laser Welding, Constant Power (CP), Gradient Power (GP)) and oscillation frequency on the weld morphology, porosity, and microstructure was examined by Optical Microscopy (OM), Electron backscatter diffraction patterns (EBSD) and industrial Computed Tomography (CT). The results demonstrated that at the same frequency, the weld depth-to-width ratio in GP mode exceeded the CP mode. The strong stirring effect promoted the pores to escape and increased the heterogeneous nucleated particles of the molten pool, which yielded the lowest weld porosity and the largest equiaxed crystal ratio in GP mode. The mechanism of porosity removal and grain refinement was determined based on the calculated energy distribution. This study provides a brand new approach for porosity inhibition and microstructure optimization of laser-welded aluminum alloys.

Effects of sidewall grain growth on pore formation in narrow gap oscillating laser welding

How to suppress the pores is one of the most important challenges in narrow gap laser welding of aluminum alloys. In order to solve this question, narrow gap oscillating laser welding (O-NGLW) of dissimilar AA6061 and AA2024 aluminum alloys was carried out. With the increase of the laser oscillation frequency (f), the pores changed from the dense and linear chain at weld center to the scattered distribution segregating at AA2024 side, and disappeared when f ≥ 400 Hz. The normalized calculated stirring Reynolds number of O-NGLW was 1369 when suppressing the pores totally, 1.39–1.75 times that of the welding without narrow gap, indicating that a stronger stirring effect induced by laser oscillation was needed to capture the bubbles. The theoretical analysis suggested that this phenomenon was closely related to the effect of columnar grains growth on bubble interception (ECGGBI). Based on the interaction between ECGGBI and the stirring effect induced by laser oscillation, the pore formation was discussed, and the reason why stronger stirring effect was needed to suppress the pores was revealed.

Numerical investigation of asymmetric weld fusion geometry in laser welding of aluminium alloy with beam oscillation

In this work, the asymmetric weld fusion geometry in oscillating laser beam welding (OLBW) of aluminium alloy was reported and investigated using a numerical approach. A multi-physics heat transfer and fluid flow model of OLBW was developed and validated with the corresponding experimental results. The weld fusion geometry, temperature fields, and fluid flow behaviours for four commonly used oscillation modes, line, circle, eight, and infinity, were calculated to analyse the origin of the asymmetric weld fusion geometry. The results show the asymmetry of local heat input along beam travelling path and the fluid flow pattern in the molten pool are the main factors that result in the asymmetric weld fusion geometry in OLBW.

Analysis of laser-beam absorptance and keyhole behavior during laser keyhole welding of aluminum alloy using a deep-learning-based monitoring system

Laser welding of aluminum alloys is a highly complex and unstable process owing to the high reflectivity and high thermal conductivity of aluminum and vaporization of alloying elements. Laser-beam absorptance is one of the factors that greatly influences the process stability, but it is very difficult to measure with conventional monitoring systems. In this study, the laser-beam absorptance and keyhole behavior during the fiber laser welding of Al 5052-H32 was investigated using a deep-learning-based monitoring system. In this method, two synchronized coaxial high-speed cameras were used to simultaneously observe the top and bottom specimen surfaces. From the obtained images, top and bottom keyhole apertures were detected by using an object-detection deep-learning model. Then, a ResNet-based deep-learning model was applied to the detected keyhole top and bottom apertures to predict the time-varying laser-beam absorptance inside the keyhole considering multiple reflections. By analyzing the monitoring results, we classified the keyhole behavior and absorption patterns into three types, and investigated the process stability and defect formation mechanisms. It was found that, when the keyhole opened constantly under excessive energy conditions, the keyhole size continued to increase and burn-through defects were generated if the aperture area exceeded the threshold values. Furthermore, process stability was improved and defect formation was suppressed by using helium as a bottom-side shielding gas under high-energy-density conditions.

Effect of magnetic field orientation on suppressing porosity in steady-magnetic-field-assisted aluminum alloy deep-penetration laser welding

The steady magnetic fields were utilized to decrease the porosity of aluminum alloy laser welded joints, and the effect is related to the magnetic field orientation. The influence of the magnetic field orientation on the suppression of porosity was investigated by establishing a three-dimensional heat flow model coupled with magnetohydrodynamics (MHD) and free surface of a keyhole. The Lorentz force decreased the backflow velocity toward the keyhole wall when the magnetic fields were horizontally parallel to the welding direction (magnetic field X-axis, MFX) and perpendicular to the welding direction (magnetic field Y-axis, MFY), thereby clearly improving the keyhole stability. Additionally, the melt flows in the rear region of the molten pool were suppressed downward and forward under the MFX and MFY, respectively, leading to additional heat accumulation in the rear periphery of the molten pool. As a result, a long molten pool in the longitudinal section and a small penetration depth were observed under the MFX and MFY. Therefore, the porosity defects decreased from 9.4% to 3.5% and 3.2% under the MFX and MFY, respectively. However, many pores were observed when the magnetic field orientation was vertical (magnetic field Z-axis, MFZ), owing to the high penetration depth and poor keyhole stability. This study provides a deeper understanding of the effect of magnetic fields on the laser welding of aluminum alloys and potentially lays a foundation for the adjustment of suitable magnetic field parameters toward obtaining the desired effect.

A Survey of Process Monitoring Using Computer-Aided Inspection in Laser-Welded Blanks of Light Metals Based on the Digital Twins Concept

The benefits of laser welding include higher production values, deeper penetration, higher welding speeds, adaptability, and higher power density. These characteristics make laser welding a superior process. Many industries are aware of the benefits of switching to lasers. For example, metal-joining is migrating to modern industrial laser technology due to improved yields, design flexibility, and energy efficiency. However, for an industrial process to be optimized for intelligent manufacturing in the era of Industry 4.0, it must be captured online using high-quality data. Laser welding of aluminum alloys presents a daunting challenge, mainly because aluminum is a less reliable material for welding than other commercial metals such as steel, primarily because of its physical properties: high thermal conductivity, high reflectivity, and low viscosity. The welding plates were fixed by a special welding fixture, to validate alignments and improve measurement accuracy, and a Computer-Aided Inspection (CAI) using 3D scanning was adopted. Certain literature has suggested real-time monitoring of intelligent techniques as a solution to the critical problems associated with aluminum laser welding. Real-time monitoring technologies are essential to improving welding efficiency and guaranteeing product quality. This paper critically reviews the research findings and advances for real-time monitoring of laser welding during the last 10 years. In the present work, a specific methodology originating from process monitoring using Computer-Aided Inspection in laser-welded blanks is reviewed as a candidate technology for a digital twin. Moreover, a novel digital model based on CAI and cloud manufacturing is proposed.

Study of mode transition in three-dimensional laser beam oscillating welding of aluminum alloy

Although 2-d (two-dimensional) beam oscillation can reduce the porosity defects during laser welding of aluminum alloys, it distributes the heat input, resulting in a higher power required to form a capillary. Therefore, this research draws attention to an alternative approach, which is considered to be beneficial to laser absorption in oscillation laser beam welding, 3-d (three-dimensional) oscillation of the laser beam. (3-d oscillation means that the laser spot moves on the two-dimensional plane and the defocus change simultaneously, causing the heat input to change) An experiment was designed where the variation of oscillation frequency leads to significant changes in capillary behavior. The result shows that the increase of vertical oscillation can promote the formation of a capillary. When the oscillation frequency reaches some special values, the capillary appears and disappears periodically, such as the vertical oscillating frequency is 5 Hz, rotation oscillating frequency is 200 Hz. Meanwhile, welding pores are generally distributed at the position where the capillary begins to disappear. The reason for promoting capillary formation during 3-d laser beam oscillation, and the change of normalized temperature, which is meaningful for understanding the welding mode transition, is illustrated by a simplified model. Compared with traditional linear welding, the experimental results show that it is possible to obtain lower porosity seam during 3-d laser beam oscillation welding in low feed rate, and the mechanism of stabilizing the molten pool is discussed qualitatively.

Fibre laser welding of aluminium alloys of 7xxx series (Al–Zn–Mg–Cu) by nonthrough thickness welds

The Paton Welding Journal, 2022, №04. International Scientific-Technical and Production Journal «The Paton Welding Journal» «The Paton Welding Journal» has been published monthly since 2000 in English, ISSN 0957-798X. «The Paton Welding Journal» is a cover-to-cover English translation of the «Avtomaticheskaya Svarka» (Automatic Welding) journal. The «Avtomaticheskaya Svarka» journal has been published monthly since 1948 in Russian, ISSN 005-111X.

Study on the molten pool behavior and porosity formation mechanism in dual-beam laser welding of aluminum alloy

Based on the mechanism of dynamic coupling between molten pool and keyhole, a three-dimensional (3D) transient model for the dual-beam laser welding of aluminum alloy is established by considering the surface tension, Marangoni force, and recoil pressure. The morphology of the molten pool, porosity formation process, and the heat transfer mechanism during the process of laser welding under different parameters are analyzed. A double rotating 3D Gaussian heat source is used to represent the laser beam, and the volume of fluid method is used to track the gas-liquid free surface, and the gas-liquid interface force is transformed by the continuous surface force model. The results show that in the process of dual-beam welding, the interaction between the two keyholes enhances the fluid flow perpendicular to the spot line, and the shape of weld pool surface changes from elliptical to circular. Furthermore, welding speed and spot spacing have a significant effect on the shape of the molten pool. Furthermore, it is observed that dual-beam welding can improve the stability of the keyhole and reduce the maximum oscillation amplitude and the number of keyhole breakups. At a specific spot spacing, a unique process of separation and fusion is discovered in addition to the common stages of growth, maintenance, breakup, and shrinkage of the keyhole. The simulation results are in good agreement with the existing experimental results. Overall, this paper provides useful insights into the dynamics of the molten pool in dual-beam welding and reveals the molten pool behavior and porosity formation mechanism.

Effect of activating flux Cr2O3 on microstructure and properties of laser welded 5083 aluminum alloys

The keyhole was very unstable in the laser welding of aluminum alloys, which was liable to cause welding defects. To solve this problem, the active laser welding (ALW) and the active laser wire filling welding (ALWFW) of 5083 aluminum alloys were investigated with a low laser power. The effect of the activating flux Cr2O3 and process parameters on the weld morphology, the microstructure, the Mg loss, the phase distribution and tensile properties were analyzed. The results showed that the 5083 aluminum alloys with 2 mm thickness were fully penetrated by ALW at a laser power of 1.5 kW. Although the welding process was free of spatter, the weld sagging and the reduction in Mg concentration were serious. With filler wires, the joint morphology changed from concave to flat. In addition, the Mg concentration was supplemented and the β phase was increased. The Al8Cr5 phase generated in the fusion zone was suggested to be the main reason for the increase of the joint strength. The maximum joint strength reached 275 MPa in ALWFW of 5083 aluminum alloys.

Numerical investigation of weld bead porosity reduction in the oscillating laser T-joint welding of aluminum alloy

T-joint welding is widely used in the assembly process of automotive, aerospace, and other industries. The pore defect is easily formed in the weld bead during the laser T-joint welding of aluminum alloy. In this paper, a three-dimensional numerical model of the oscillating laser T-joint welding of aluminum alloy with presetting solder patch is established to reduce pores in the weld. Both the molten pool dynamic behaviors in the oscillating laser T-joint welding and non-oscillating laser T-joint welding are analyzed by the numerical simulation results. It is found that the porosity of weld bead can be reduced by the dynamic behaviors in the oscillating laser welding. The reduction process of porosity in the oscillating laser T-joint welding of aluminum alloy is discussed in detail. The numerical calculation results are compared with that of the experiments and good agreement between them is found. Therefore, the proposed method is of great importance for reducing the weld bead porosity in laser welding of aluminum alloy and achieving the high quality welding process.

Effect of ambient pressure on laser welding of AlSi10Mg fabricated by selected laser melting

This work attempted to introduce high pressure to reduce pore generation in laser welding of selective laser melted AlSi10Mg, which is different from the traditional approach where the vacuum was preferred in laser welding of aluminum alloys. To understand these phenomena, the impacts of laser welding parameters and ambient pressure on the porosity and weld geometry were examined. Porosity ratio was found linearly increasing with the laser power or linear energy. High-speed imaging revealed that the large pores were formed by multiple merging of small pores, which explained the decrease in fine porosity (<20 μm) but increase in coarse porosity (50–100 μm) when increasing laser power or linear energy. The vacuum ambiance significantly enlarged the pores (up to ∼400 μm) and formed narrow and deep welds. As pressure increased from 0.1 MPa to 0.4 MPa, the porosity ratio was dramatically decreased from ∼10.2% to ∼2.3% accompanied by a decline in porosity size and weld penetration depth. Numerical simulation results revealed that the shallowed weld penetration under high-pressure ambiance was attributed to the decreased recoil pressure, and the reduced porosity ratio was resulted from the high pressure which limited pore growth and merging.