Laser Welding Of Aluminum Research Articles

Interpretation of mechanical properties gradient in laser-welded joints: Experiments and grain morphology-dependent crystal plasticity modeling

The grain size and morphology of laser welds show a gradient distribution, leading to variations in mechanical properties. This study proposes a microscopic crystal plasticity constitutive (CPC) model to examine the effect of ER4047 welding wire on the mechanical properties of laser-welded aluminum alloy joints. A finite element model updating strategy was used to fully invert the morphological mechanical parameters, marking a significant advancement. This study combines mesoscale electron backscatter diffraction (EBSD) observations with macroscopic uniaxial tensile tests to obtain crystal plasticity finite element analysis and strain field data from digital image correlation. The mechanical property gradient of the welded joints was systematically analyzed from a crystal perspective. The CPC parameters were inverted for different grain sizes and morphologies. The study found that using ER4047 welding wire significantly enhanced the mechanical properties of the welded joints, especially in the welding zone. As grain size increased, the yield strength of the material decreased, while the hardening modulus increased. Additionally, the cast characteristics of columnar crystal morphology reduced both yield strength and hardening modulus.

Computational modeling and virtual analysis using a moving heat source to join AZ61A and AA7075 alloys with the application of a titanium alloy interlayer

Laser beam welding (LBW) uses a concentrated laser beam to fuse materials, providing benefits such as a smaller heat-affected zone (HAZ), speed, accuracy, adaptability across multiple materials, and seamless adoption into automation processes. Achieving optimal weld quality with LBW remains difficult due to the need to select the appropriate welding process variables and proper interlayer between dissimilar materials. Due to the high cost and safety risks to operators and equipment in LBW, it is challenging to use the practical experiment. Additionally, welding materials with high thermal conductivity and lower melting temperatures, such as AZ61A and AA7075, is a considerable challenge. Previous research focused on process parameters in laser beam welding of various metals, but not enough consideration has been given to the effect of a titanium interlayer on AA7075 and AZ61A using virtual data. This study aims to fill these gaps by using simulation data to assess the effects of process parameters and the titanium interlayer during LBW of dissimilar materials. A backpropagation neural network with the gradient descent learning rule was used for optimization, and a central composite design was used to predict the optimal process parameter interaction. The result indicates the optimum equivalent strain is obtained at the values of beam radius between 4.5 to 5 mm. The maximum equivalent stress reached during welding speed is between 4 to 4.5 mm/s. The maximum residual stress was obtained at the number of segments of 160. The predicted maximum and average anticipated errors for peak temperature are 0.1655 % and 0.0210 %, while for residual stress it is computed as 0.1766 % and 0.0754 %. The Ti-interlayer in magnesium and aluminum laser welding reduces peak temperatures, allows for uniform energy distribution, minimizes localized heating, and enhances weld quality while lowering residual stress.

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.

Resistance analysis of laser-welded aluminum lead and tab for electric vehicle battery: Experiment and simulation

In pouch-type Li-ion batteries used in electric vehicles, battery cell tabs are electrically connected to an external lead of the same substance. Laser welding is a promising technique for joining these materials. This study investigates the fundamental question of whether electrical resistance measurements can be used to reliably estimate the welding state. An Al lead (400 μm thick) was welded spot-by-spot to a stack of 30 Al tabs (each tab 13 μm thick) using a laser beam incident on the lead surface. By adjusting the laser irradiation conditions, three different welding states (shallow, intermediate, and deep states) were intentionally produced. However, these structures exhibited no appreciable difference in the resistance measured across the welded region. The resistance was on the order of 10−4 Ω regardless of the welding state. Simulations were conducted for various joint structures, including those with voids, to derive the current flow through the structures and joint resistances. The simulation results corresponded well with the experimental results. Our study indicates that the electrical estimation of the welding state is challenging, because extremely low resistances are obtained even if the lead and tab are locally connected with narrow current paths.

In-situ monitoring of Al/Cu dissimilar laser welding process using optical emission spectroscopy (OES)

Aluminum (Al) and copper (Cu) dissimilar laser welding is an in-demand process in the manufacture of secondary battery systems for electric vehicles. However, the absence of a robust in-situ monitoring technique for this process reduces its efficiency and increases the potential risk to the battery system. Laser-induced plasma (LIP) has been extensively studied in various laser processes because it provides crucial information regarding the interaction between the laser beam and material. In this study, the measurement of LIP was conducted using optical emission spectroscopy (OES) during the Al and Cu dissimilar welding process to gain a comprehensive understanding of the process. Moreover, the feasibility of OES as a monitoring tool for dissimilar laser welding of Al and Cu was evaluated. Plasma parameters such as emission line intensity, electron temperature, and number density were effectively used to diagnose the welding state (non-welding, threshold welding, or Cu-penetrated welding). In addition, a strong correlation between the weld geometry and intensity of the Cu emission line was found. This study demonstrates the considerable potential of OES-based in-situ monitoring system applicable for high-demand dissimilar laser welding processes.

Effect of laser welding strategy for reducing intermetallic compound formation and residual stress

Reductions in automobile weight and carbon dioxide emission are critical for the further development of the automobile industry. Aluminum is a lightweight material that can replace copper in automobile electronic equipment; therefore, laser welding of aluminum and copper is a subject of extensive research. This study investigates the influence of the laser strategy on the laser welding of aluminum and copper while preventing the formation of brittle Al–Cu intermetallic compounds. Aluminum and copper plates with a length of 20 mm and thickness of 0.3 and 1 mm, respectively, are used for the experiment. A continuous-wave laser with a power of 500 W and a spot beam radius of 150 μm is employed to irradiate the aluminum surface at different scan speeds. An electroless-plated nickel layer is used as a buffer between aluminum and copper, and the experimental results show that it can prevent copper surface damage and the formation of Al–Cu compounds during laser welding. In addition, the simulation and experimental results reveal that the residual thermal stress after laser welding can be reduced by heat treatment at different temperatures prior to laser irradiation.

Frontal pyrometric snapshot measurements of the keyhole wall temperature in laser welding of pure aluminium

In deep penetration laser welding, the quality of the weld seam is strongly correlated with the process dynamics. Pronounced dynamics of the melt pool and the keyhole cause defects like pores and blow-outs which negatively affect the mechanical properties of the seam. The process dynamics are primarily governed by the fluctuations of the keyhole shape. Therefore, in order to avoid the occurrence of defects in the weld seam, it is necessary to gain control over the keyhole stability by understanding the underlying physical processes that contribute to its dynamics. Besides the intensity distribution of the laser beam on the keyhole walls, the keyhole wall temperature is a crucial influencing factor when it comes to the assessment of the local metal evaporation rate and the induced local recoil pressure acting on the keyhole wall. Using small high-melting tantalum probes as measuring channels, temperatures in the vicinity of the Knudsen layer at the keyhole front wall were measured at different depths below the sample surface by means of high-speed pyrometry. For this purpose, bead on plate welding was conducted at low process velocities in the Rosenthal regime using pure aluminium (EN AW-1050A) as substrate material. It is shown for different laser powers and process velocities that the melt temperature in the vicinity of the keyhole wall lies in the range of 3000 K ± 400 K, therefore intermittently exceeding the vaporisation temperature of the substrate material. Significant correlations between the keyhole wall temperature and the laser power as well as the measuring depth could not be identified.

Probing the impact of process variables in laser-welded aluminum alloys: A machine learning study

This paper presents a pioneering approach, Bayesian machine learning (ML), for the estimation and characterization of critical laser welding features in Aluminum alloys, encompassing peak temperature, heat-affected zone width, and bead aspect ratio. The methodology involved constructing a laser welding database utilizing finite element simulations (FEM). The distinctive advantage of the Bayesian ML model lies in its capability to address challenges associated with excessive approximation and to account for uncertainties in parameters. This results in precise and resilient predictions of laser weld parameters across a spectrum of aluminum alloys. The findings underscored the model's efficacy in forecasting output targets, although regression analysis unveiled unique characteristics in data distribution and outliers specific to aluminum alloys. These outliers were primarily linked with the melting range of aluminum alloys, leading to the Al7075 alloy having the lowest prediction, and the Al1100 alloy the highest within the ML model. Additionally, the normalized average weight functions of input parameters were illustrated, clarifying their differing importance concerning diverse types of Al alloys in precisely forecasting output objectives. In light of these explanations, it remains consistent that laser power (LP) and welding speed (WS) inputs hold substantial sway across all alloys, while workpiece thickness (WT), beam diameter (BD), and initial temperature (IT) played comparatively lesser roles. Ultimately, this work contributes to a more profound comprehension of the relationships between input features and the geometrical and thermal behavior of laser-welded Al joints.

Effect of different pulse shapes on the laser welding of aluminum and copper

The Nd: YAG laser is utilized to weld 1060 aluminum (Al) and 110 copper (Cu) with a thickness of 0.4 mm. The effect of different pulse shapes on the microstructure, mechanical and electrical properties of Al-Cu lap joints are investigated by using of the optical microscopy, scanning electron microscope (SEM), tensile test device and micro-resistance tester, respectively. This investigation provided a detailed understanding of how the different pulse shapes influence the metal mixing and the formation of intermetallic compounds (IMCs). The results indicate that the pulse shape with an initial preheating phase improved the laser absorption efficiency. Additionally, this pulse shape resulted in less dissimilar metal mixing compared to the pulse shape that maintained the maximum power throughout. Furthermore, the pulse shape in which the laser power was linearly increased and then maintained at maximum power reduced the formation of IMCs at the joint interface. As a result, the joint exhibited mechanical strengths up to 92 % of the Al base material and similar electrical conductivity. The study provides theoretical guidance on how to utilize pulse shape modulation in laser welding to achieve optimal mechanical and electrical properties in typical joints between Al tabs and Cu busbars.

Porosity inhibition of aluminum alloy by power-modulated laser welding and mechanism analysis

Porosity is a significant issue when conducting laser welding (LW) of aluminum (Al) alloys. Laser oscillating welding appears a good choice for suppressing porosity, but it is accompanied by energy losses. To address the above issues, this paper proposes an innovative power-modulated LW system that simultaneously achieved porosity suppression, power modulation, and energy loss reduction. To demonstrate the effectiveness of the system, comparative experiments were performed using three welding modes: conventional LW, constant power (CP) laser oscillating welding, and gradient power (GP) laser oscillating welding. The results of the experiments indicated that the GP mode was more effective at reducing porosity and the weld depth was greater than that of the CP mode. Numerical simulations were conducted to describe this process. The results showed that changes in the molten pool (MP) flow behavior of the GP mode determined the welding effect. The physical mechanism by which the GP mode suppressed porosity and reduced energy losses was revealed.

Quality classification model with machine learning for porosity prediction in laser welding aluminum alloys

The growing implementation of aluminum alloys in industry has focused interest on studying transformation processes such as laser welding. This process generates different kinds of signals that can be monitored and used to evaluate it and make a quality analysis of the final product. Internal defects that are difficult to detect, such as porosity, are one of the most critical irregularities in laser welding. This kind of defect may result in a critical failure of the manufactured goods, affecting the final user. In this research, a porosity prediction method using a high-speed camera monitoring system and machine learning (ML) algorithms is proposed and studied to find the most performant methodology to resolve the prediction problem. The methodology includes feature extraction by high-speed X-ray analysis, feature engineering and selection, imbalance treatment, and the evaluation of the ML algorithms by metrics such as accuracy, AUC (area under the curve), and F1. As a result, it was found that the best ML algorithm for porosity prediction in the proposed setup is Random Forest with a 0.83 AUC and 75% accuracy, 0.75 in the F1 score for no porosity, and 0.76 in the F1 score for porosity. The results of the proposed model and methodology indicate that they could be implemented in industrial applications for enhancing the final product quality for welded plates, reducing process waste and product quality analysis time, and increasing the operational performance of the process.

Study of the brittleness mechanism of aluminum/steel laser welded joints with copper and vanadium interlayers

Intermetallic compounds (IMCs) generated by direct laser welding of aluminum and steel decrease the strength of the joint. To evaluate the effect of alloying elements on the weldability of aluminum/steel dissimilar materials, the copper (Cu) and vanadium (V) were introduced into the interlayer to inhibit the generation of Fe-Al IMCs. Comparing with direct welding, Cu promotes the generation of Al2Cu and V transforms the disordered Fe/Al interface into a continuous Al/V interface to promote the generation of Al3V and Al21V2. In addition, the first-principles calculations were carried out to study the elastic properties and electronic properties of intermetallic compounds. The results show that high brittleness of FeAl, Fe2Al5 and FeAl3 results from strong covalent bonding and antibonding. The Fe(d) orbit hybridizes with Al(s) and Al(p) orbits while resonant peaks and wide pseudogap appear in the density of states. The low brittleness of Al2Cu results from the less count of covalent bonds with 76.2% of weaker antibonding; the low brittleness of Al21V2 results from the lower covalent bond strength with a maximum overlap bond population of 0.265. With the addition of Cu, the strength of the joint was increased to 63 MPa from 31 MPa. Furthermore, the addition of V completely prevents the formation of Fe-Al IMCs, which results in the highest joint strength (93 MPa). The results of the first-principles calculations and experiments are in good agreement.

A Weldment Characteristics on Laser Welding of 2XXX Aluminum Alloys

In the aerospace industry, high-strength heat-treated aluminum alloys are increasingly being used for large wing structures, which are typically designed by welding thin skins to a pocketed frame structure to reduce weight. Owing to the limited welding area between the frame and the skin and the limited space in the chamber, laser welding is the most suitable manufacturing process. Therefore, the weld-ability and the strength of laser-welded aluminum frame-skin structure must be determined. In this study, AA2219 of the A2XXX alloy series was tested under various welding conditions. Analysis of the bead shape in the cross-section of the welded frame?skin revealed that the optimal welding conditions can be achieved when the ratio of the bead width to penetration (L/H) is minimal. The weld-ability of AA2219 was compared to that of AA2024 by examining the 1) spatter and porosity, 2) hardness in the heat-affected zone, and 3) tensile strength of the two alloys welded under the determined optimal welding conditions. The tensile strength of laser-welded AA2219 and AA2024 was 79% and 70% of that of the base material, respectively. Because the tensile strength value of the welded AA2219 was nearly equal to the yield strength value of the base material, the AA2219 laser-beam welding process can be applied to large wing structures.

Prediction of the influence of welding metal composition on solidification cracking of laser welded aluminum alloy

The crack length of laser welding 6082 aluminum alloy with three types of 5000 series aluminum alloy welding materials was compared by fishbone test method. It was found that ER5A06 welding material corresponds to the shortest crack length, indicating that the welding material composition has an impact on the welding crack and the crack susceptibility could be controlled by adjusting the welding material composition. Combined with SEM and EBSD, the crack morphology was observed and determined to be solidification cracking. Through EDS, EPMA and thermodynamic calculation, it is found that the main elements affecting solidification cracking are Al, Mg, Si and Cu. The cooling rate of the fusion zone was calculated according to the secondary dendrite arm spacing and welding composition. Compared with casting and arc welding, the laser welding aluminum alloy fusion zone has rapid cooling rate. Due to the rapid cooling rate, the T-fs curves of Al-Mg, Al-Si and Al-Cu binary alloys were calculated by commercial thermodynamic software Thermo-Calc. Furthermore, the cracking susceptibility index (CSI) of binary aluminum alloys were also calculated to determine the element content range of the cracking. To understand the element interaction, both the machine learning and computational thermodynamic methods were employed to predict the influence of multi-component welding metal on solidification cracking susceptibility. Based on the calculation results of solidification cracking susceptibility for binary aluminum alloys, a data set containing 45 groups of aluminum alloy components was established and set as the input dataset. The CSI values corresponding to the compositions in the data set were set as the target and the relationship “welding metal composition - CSI” was founded. Based on the Kriging model, the influence of welding metal composition on solidification cracking susceptibility and the components of most crack susceptible were obtained, which provides a basis for welding materials design.

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.

ALUMINUM AND STEEL WELDING WITH 500 W FIBRE LASER

The study of the process of laser welding of various aluminum-steel joints is necessary to promote the possibility of realization of new products and designs in instrumentation and mechanical engineering. Laser welding, due to its many advantages, is considered a very promising process of joining different materials, although its application in industry is still limited. Welding aluminum with steel using laser sources is a challenging task mainly due to the formation of brittle intermetallic joints (IMC) at the joint interface. This paper aims to give a brief overview of some new research on laser welding of aluminum to steel, as well as to point out some of our initial laboratory research in this direction.[1]

The role of filler material selection in the laser welding process of deformable 6xxx series aluminum alloys

The automotive industry is facing stringent requirements regarding the reduction of fuel consumption and the reduction of greenhouse gas emissions. The use of aluminum alloys and laser welding technology allows the fulfillment of these targets by creating the opportunity to decrease the weight of the vehicles. One of the variables related to the laser welding process is the filler material. In the case of heat-hardenable alloys, the role of the filler material is to adjust the chemical composition of the molten metal bath and to reduce the sensitivity to hot cracking. In this paper is examined and interpreted the effect of the additive materials selected at the laser welding of some alloys with aluminum base of the 6xxx series on the macro – and the microstructure of the welded joints.

Emissivity Prediction for an IR Camera During Laser Welding of Aluminum

Laser processing is becoming increasingly important in industrial applications. The success of the process relies on two fundamental parameters: the surface temperature of the medium and the thickness of the hardened layer. One of the most important factors during a laser process is certainly the temperature, which presents high temperature gradients. The speed at which a material undergoes a phase transition, the chemical reactions that take place during processing and the properties of the material are all dependent on temperature changes. Consequently, the measure of temperature is a demanding undertaking. This study proposes to measure temperature for the duration of laser welding with the infrared camera (IR) Optris PI. To restore the real temperature based on the brightness temperature values measured by the IR camera is needed to evaluate the emissivity to be attributed to the IR camera. For this purpose, firstly, the isotherms consistent with the melting point of aluminum (785 K) were assessed and then compared with the temperature distribution gauged in the zone of irradiation of the laser. Such data were then compared with the thickness of the melted zone. The use of the melting point isotherm allowed the calculation of the value of emissivity and the restoration of the temperature. Thermography software data acquisition wrongly presupposes the emissivity value does not change. This generates incorrect thermographic data. The surface emissivity normally hinges on temperature. Therefore, the values on which the literature relies may not work for materials of interest in the conditions of the process. This is particularly the case, where welding is carried out in keyhole mode (Tmax = Tvap). However, the physical phenomena involved, including evaporation and plasma plume formation, high spatial and temporal temperature gradients, and non-equilibrium phase transformations, influence the optical conditions of the brightness of the emission of light from the molten pool, making, De Facto, the emissivity value not constant. Thus, what we propose here is a methodological procedure that allows the measurement of the effective emissivity of the surface, at the same time taking into consideration the consequence of physical phenomena and the conditions of the surface. Two procedures (Standard and Simplified) capable of providing the correct emissivity value in relation to the working parameters have been proposed. The results showed that the procedures are correct, fast, and easy to use.

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.

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.