Welded Aluminum Alloy Research Articles

In-situ EBSD-DIC simulation of microstructure evolution of aluminum alloy welds

A comprehensive understanding of the dynamic evolution of weld microstructure under external loads can provide key insights for high-performance laser welding. A novel in-situ EBSD-DIC simulation method is introduced to study the microstructure evolution of laser welded aluminum alloys under uniaxial tensile action. An advanced crystal plastic finite element model (CPFEM) is developed, which combines the real microstructure, grain orientation and grain size effects. The results show that the dislocation density in columnar grain zone is higher than that in equiaxed grain zone. The continuous accumulation of dislocations in the columnar region results in a high work-hardening rate. This high work hardening rate enhances the plastic deformation capacity of the columnar crystal region, resulting in local strain concentration. Columnar zones are more prone to fracture because the high-strain region is a potential fracture site. In addition, low Angle grain boundary (LAGBs) is one of the reasons that the dislocation density of the columnar grain zone is higher than that of equiaxed grain zone during tensile process, which is conducive to dislocation slip of columnar grains. This study is a fundamental innovation in simulating the microstructure evolution of laser welding. This marks a major breakthrough in simulating the evolution of crystallographic features such as grain orientation, microstress and strain and dislocation density under external loads. This work can further provide practical guidance for “microstructure characteristics - mechanical property regulation”.

Effect of Process Parameters on the Mechanical Properties of Simultaneous Double-Sided Friction Stir Welding Joints

Currently, conventional single-sided friction stir welding is primarily suitable for joining thin plate aluminum alloys, and its application to thick plates is still challenging in terms of welding efficiency and joint mechanical properties. Simultaneous double-sided friction stir welding (SDS-FSW) is a high-efficiency joining technique specifically developed for welding thick plates. However, there is little research on the influence of SDS-FSW process parameters on the joint mechanical properties. In this study, a 12 mm thick AA6061-T6 aluminum alloy and dual robot welding equipment are used to conduct SDS-FSW experiments exploring the influence of rotational speed ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} and welding speed v on the mechanical properties and microstructure. The results show that when the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 60–80 mm/min, smooth and defect-free thick plate aluminum alloy SDS-FSW joints can be obtained, and the macroscopic morphology of the joints is distributed in a “dumbbell” shape. The grain size in the weld nugget zone increases with increasing welding heat input. The microhardness distribution in the joint displays a “W” shape, and the hardness value of the weld nugget zone can reach 67% to 86% of that of the base metal (BM). The junction between the thermo-mechanically affected zone and the heat affected zone is the weakest region of the joint, with the lowest hardness being approximately 51% of that of the BM. When the welding parameters are ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} = 800 r/min and v = 140 mm/min, the SDS-FSW joint has the highest tensile strength, reaching 78.43% of the BM strength and exhibiting ductile fracture characteristics. This research indicates that acceptable weld strength in thick aluminum alloys can be achieved via the SDS-FSW joining mechanism, highlighting its significant potential for industrial applications.

Optimal Tungsten Inert Gas Welding Parameters of Dissimilar Aluminum Alloys Al 7075 and Al 6061 Using Ultrasonic Vibration and Nanocomposite Filler (Al 5356/ZrB2) to Alleviate Hot Cracking Phenomenon

Abstract In this study, the welding of dissimilar aluminum alloys, Al 7075 and Al 6061, was investigated using Al 5356 filler rods reinforced with ZrB2 particles. The welding process was conducted using tungsten inert gas (TIG) welding, with and without ultrasonic vibration, to enhance weld quality and reduce hot cracking. Optimization of process parameters for dissimilar TIG welding was performed through Response Surface Methodology (RSM), which generated a design matrix to analyze the influence of process parameters on response variables. Numerical and graphical optimization was applied to minimize hot cracking sensitivity and maximize microhardness. The RSM-based models suggested an optimal welding current of 93 A, the use of Al 5356/ZrB2 nanocomposite filler, and the application of ultrasonic vibrations. Experimental validation of the identified solution demonstrated improvements in weld quality, including increased yield strength and ductility. The combination of nano-reinforced fillers and ultrasonic vibrations was found to enhance weldability and mitigate hot cracking in dissimilar aluminum joints. The mechanism of hot cracking reduction involved grain refinement, degassing, and homogenization due to ultrasonic vibrations, as well as the modification of weld pool chemistry and control of dilution by the nanocomposite filler, which collectively minimized solidification shrinkage and stress. Under these optimized conditions, no hot cracking was observed experimentally.

Experimental study on high-precision measurement of surface temperature in friction stir welding aluminium alloy 2219 based on infrared thermometry

In friction stir welding (FSW) of aluminium alloy 2219, the welding temperature critically influences the weld quality. Accurate measurement of the welding temperature is essential for effective welding process control. However, the conventional approach of non-contact infrared thermometry faces significant challenges in FSW due to the inherently low and variable emissivity of aluminium alloys, making it susceptible to environmental radiation interference. This paper proposes a novel, high-precision method for measuring the surface temperature of FSW aluminium alloy 2219 based on infrared thermometry principles. Initially, the study delves into these principles, analysing factors that affect the accuracy of infrared thermometry in the context of FSW in industrial settings. To enhance the surface emissivity of the weldments, a high-emissivity coating is applied to the aluminium alloy surface. Additionally, strategic adjustments in the positioning of the thermal imager and careful selection of the measuring area effectively mitigate interference from the FSW tool’s radiation. Conventional methods report a temperature measurement error greater than 2%, while the proposed method reduces this error to 1.2%. The effectiveness and practical utility of the method are validated through FSW experiments on flat plates and rocket tank rings, corroborated by comparative analyses with surface thermocouple temperature measurements. This confirms the viability of the proposed method for high-precision temperature measurement in aluminium alloy FSW applications.

Enhancement of the mechanical properties of semi-stationary bobbin tool friction stir welded joints in AA2219 through post-weld heat treatment

This research investigates the enhancement of AA2219 joints formed by semi-stationary bobbin tool friction stir welding (SSBT-FSW) through post-weld heat treatments. Although solid-state processes such as SSBT-FSW are able to produce superior welds without common defects seen in conventional fusion welding of aluminum alloys of the 2XXX series, the thermal cycle in SSBT-FSW can deteriorate mechanical properties by causing precipitate dissolution and over-aging. The research proposes using a heat treatment sequence to induce solubilization and re-recipitation of precipitates in a more favorable distribution, re-activating the precipitation-hardening. Since abnormal grain growth is very difficult to avoid during heat treatments of welded samples, the analysis focuses on the evolution of the microstructure during solution heat treatment and on the influence of grain size, texture, and precipitate distribution on grain growth. The origin and evolution of the grain growth during solution heat treatment have been observed. Hardness measurements and tensile tests show that post-weld heat treatments can effectively restore the mechanical properties of the joints to the levels of those of the base material. Understanding the relationships between microstructure, abnormal grain growth and mechanical behavior of the joints aids the optimization of the SSBT-FSW process for broader industrial application, especially in the aerospace industry, where high-performance aluminum welded structures are critical.

Study on the Electron Beam Repair Welding of 5000 Aluminum Alloys

Electron beam welding (EBW) has been attracted due to its high energy density, high depth-to-width ratio, low thermal strain, compared with arc and laser welding. In addition, it ensures high quality weld joint in structural metals in a wide range of thickness from 0.025 mm to 300 mm. Therefore, EBW is widely used in industries such as automotive, aviation, nuclear power plant, etc. Although a lot of studies on EBW for several decades have been presented, EB based repair welding with supplement of filler metal has less reported. In this work, EB repair welding for 5083 aluminum alloys was investigated because the aluminum alloys are becoming more important as a lightweight material in mobility industries. Material characterization and mechanical properties of the repair-welded specimens were evaluated, compared with characteristics of base metal and bead welding without repair. The optimized experimental conditions showed tensile strength of 294 MPa, which is a similar to base metal. Our study indicates that EB repair welding can be considered for the candidate of repair welding of aluminum alloys.

Formation of the Interlock Morphology and Its Role in Refill Friction Stir Spot Welding of Aluminum Alloy to Steel

Considering energy conservation and emission reductions, lightweight automobiles have become a research focus in the automotive industry. Steel/aluminum joining is regarded as an ideal lightweight structure, which can not only reduce the energy consumption but also ensure safety and is already attracting extensive attention. In this study, aluminum alloy 6061 and B410LA steel sheets were successfully joined by refill friction stir spot welding. The tensile properties, microhardness distribution and interfacial microstructure characteristics of the steel/Al welded joints were investigated. The maximum tensile load of the steel/Al joint was 4.3 kN. The mechanical properties of the steel/Al refill friction stir spot welded joint were largely determined by the bonding quality of the sleeve-plunging zone. With the stirring of the sleeve and the pin during the refill friction stir spot welding, work hardening occurred in the stir zone (SZ). The microhardness of the SZ was significantly higher than that of the steel base metal (BM) and could be detected on the steel side. The Fe-Al intermetallic compound (IMC) layer was continuously distributed at the interface of the sleeve-plunging zone, revealing good uniformity in the thickness. In particular, a hook-and-vortex-like structure formed during the refill friction stir spot welding process in the sleeve-plunging zone, producing a mechanical interlock effect at the interface. The ideal mechanical properties of the welded joint could be attributed to the good quality of the metallurgical and mechanical bonding at the interface, especially the mechanical interlock effect, thereby depending on the hook-and-vortex-like structure.

Effects of Different Surface Treatment Methods on Laser Welding of Aluminum Alloy and Glass

Effects of Different Surface Treatment Methods on Laser Welding of Aluminum Alloy and Glass

Gap tolerance and molten pool destabilization mechanism in oscillating laser-arc hybrid welding of aluminum alloys

Oscillating laser-arc hybrid welding (O-LAHW) offers significant advantages in enhancing efficiency and mechanical properties. However, in actual production, gap fluctuations can cause instability, limiting its application in large-scale structure manufacturing. In this study, we explored the impact of gap fluctuation on the destabilization of the molten pool in aluminum alloy O-LAHW and identified the maximum gap tolerance for various conditions. High-speed photography revealed that the oscillating molten pool undergoes a transitional state of periodic collapse before complete instability, a behavior distinct from that of a non-oscillating molten pool. We also analyzed the variations in weld geometry prior to destabilization and developed a global force model of the molten pool to identify key geometrical parameters and related driving forces contributing to destabilization. The results show that maintaining a surface tension ratio of over 55 % at the root of the molten pool is crucial for its stability. Additionally, the effects of oscillatory behavior and gap variations on the laser-substrate interaction were explored, revealing the physical mechanisms behind the changes in key geometrical parameters of the melt pool cross-section. The centrifugal effect generated by high-frequency oscillation is identified as a crucial mechanism for extending the duration of periodic collapse compared to non-oscillating molten pools. By discussing the interactions between energy absorption, molten pool shape, and molten pool forces, the study reveals the evolution process of weld destabilization and explains the differences in gap tolerance between oscillating and non-oscillating laser-arc hybrid welding, providing a reference for improving weld stability.

Weld Pool Flow Characteristics in Double-Wire Arc Welding of Aluminum Alloys: Research by Numerical Simulations

Double-wire arc welding involves simultaneously feeding two wires into a molten pool, improving the efficiency and flexibility of traditional welding techniques. However, the interactions between the two wires and the molten pools are complex, which increases the difficulties in process and composition control. This work focuses on the weld pool flow characteristics in double-wire TIG arc welding. A CFD model incorporating a liquid bridge transfer model was developed to simulate the fluid flow phenomenon. Results show that the bead-forming appearances and flow characteristics of double-wire arc welding show no significant differences from single-wire arc welding. Welding current and welding speed have significant effects on the weld bead dimensions, while only welding current has effects on the flow characteristics. Wire feed XOZ angles show no significant influences on weld bead forming appearances and molten pool flow characteristics. Wire feed XOY angles influence the symmetry of the weld bead and the fluid flow. In 5B71/7055 heterogeneous double-wire arc welding, achieving a uniform distribution of alloy elements is difficult due to the complex convection patterns within the molten pool.

Influence of travel speed on porosity and liquation cracking in cold wire pulsed gas metal arc welding of aa7075-t651 aluminum alloy

Influence of travel speed on porosity and liquation cracking in cold wire pulsed gas metal arc welding of aa7075-t651 aluminum alloy

Segmentation-assisted classification model with convolutional neural network for weld defect detection

Detecting weld defects in battery trays is crucial for the safety of new energy vehicles. Existing methods for weld surface defect detection, relying on traditional computer vision algorithms and convolutional neural networks with substantial image-level labeled data, face challenges in accurately identifying small defects, especially with limited samples. To address these issues, we developed an innovative Segmentation-Assisted Classification with Convolutional Neural Networks (SACNN) model. SACNN integrates a common feature extraction subnet, a segmentation subnet enhanced by a multi-scale feature fusion module, and a classification subnet specifically designed for precise defect detection. A joint loss function co-trains the segmentation and classification subnets using both image-level and pixel-level labels, enhancing the model’s ability to accurately detect small defect regions. Our model demonstrates notable improvement, achieving accuracy gains ranging from 2% to 18% compared to existing state-of-the-art methods, with an overall accuracy of 94.09% on an industrial dataset of battery tray welds. To further evaluate the generalization capability of our model, we evaluated it on the publicly available Magnetic Tile dataset, achieving state-of-the-art results in this challenging context. Additionally, we conducted comprehensive ablation studies to validate the contribution of each component in our approach and utilized visualization techniques to enhance the interpretability of our model. These advancements represent a significant contribution to the state of the art in aluminum alloy weld defect detection.

Corrosion behavior of dissimilar Al–Mg–Si alloys joint welded under hybrid CMT-laser oscillation welding

As the corrosion behavior of 6xxx series aluminum alloys depends on composition and microstructure, the microstructure and corrosion behavior of 6082 and a new 6xxx aluminum alloy weld joint are investigated under a standard corrosion test in this study. These results show the asymmetrical welding joint structure and a distribution of corrosion severity across the weld joint. Substantial differences were observed in the size and distribution of Mg2Si particles and Fe-bearing intermetallics in various regions of the weld joint. It was found that the equiaxed grain zone on new 6xxx aluminum side is not most susceptible to corrosion, contrary to previous results, but the narrow partially melted line on 6082 side is. Not all corrosion induced by Fe-bearing intermetallics originates from the Al matrix, adjacent Fe-bearing intermetallics and Mg2Si could also form galvanic microcells, resulting in preferential dissolution of Mg2Si over the Al matrix.

Multi-scale three-dimensional simulation of the solidification microstructure evolution in laser welding of aluminum alloys under dynamic spatial thermal cycling

Laser welding process involves three-dimensional (3D) highly dynamic spatial thermal cycling that results in intricate microstructure evolution in different zones. Understanding of the 3D topological evolution of microstructure under spatial thermal cycling is crucial for effective control in solidification processes. In this paper, a 3D multiphase-field model combined with accelerated methods and multi-scale coupling algorithms was developed for high-precision prediction of the dynamic microstructure evolution in laser welding. The heat flow distribution during laser welding varied significantly, with the cooling rates of 1.7–1.9 × 104 K/s at the middle region and 7.5–9.0 × 104 K/s at the bottom region. Considering the effects of 3D heat flow, a large angle may appear between the grains' primary growth direction and the cross-sectional plane, thereby the ultimate morphology through 2D analysis may lead to distortion from reality. The simulation of 3D microstructure evolution during distinct regions results showed that the grains at the bottom region exhibited larger characteristic dimensions (Length/Height >2.5, Length/Width >2.0) and columnar shape, while the middle region tended to form equiaxed structures. The grain size statistics revealed that the grains in the middle region exhibited larger scale due to their smaller GR (G: temperature gradient, R: growth rate) values. The simulation results were in good agreement with the electro-back-scattered diffraction testing results and the theoretical analysis.

Effect of corrosion environments on the mechanical properties of friction stir welded aluminum alloy AA3003

The article presents an experimental study on the corrosion resistance of the 3003 Aluminium alloy Friction Stir Welded (FSW) joint in different working environments. Three types of corrosive media at different temperatures were tested to see how they affected the FSW joint mechanical properties. The media were sodium chloride, hydrogen chloride, and ethylene glycol. In parallel with the study of the effect of temperature, static tensile tests were carried out on specimens taken perpendicular to the welding direction. Also, micro-hardness profiles were used to determine the influence of the parameters studied on the various weld zones. Finally, the effect of the most aggressive corrosive medium, temperature, and the inclusion of ethylene glycol on the crack propagation resistance of an FSW joint were studied. Fatigue-propagation tests at constant stress amplitude were carried out to understand what affects the fatigue crack propagation of welded joints after corrosive attack. The results showed that uniform and pitting corrosion were combined to cause FSW joint surface degradation. Corrosion damage does not appear to alter yield strength and ultimate stress values. However, FSW joints show a significant degradation in mechanical properties with increasing temperature and with the aggressiveness of the corrosive medium. The inclusion of ethylene glycol was found to delay the rate of crack propagation during testing, leading to an improvement in the service life of pre-corroded FSW joints.

Influence of tool rotational speed in butt-joint friction stir welding (FSW): a thermo-mechanical simulation of AA6061

Friction Stir Welding (FSW) is a solid-state welding technique that involves joining two pieces of material by rotating a non-consumable pin at high RPM. This rotation generates heat through friction between the tool and the plates, enabling the welding process without the need for filler metal. Invented by the British Welding Institute (TWI) in 1991, FSW is renowned for creating strong welds and is widely used in the automotive and aerospace industries, in those industries the aluminum alloys are indispensable due to their unique combination of properties. This study focuses on how variations in rotational speed influence temperature distribution, the width of the heat-affected zone, and Von-Mises stress distribution in welded aluminum alloy 6061 sheets, this research aims to provide a comprehensive understanding of these effect, therefore the findings are expected to contribute to optimizing FSW parameters and enhancing weld quality. The analysis was conducted using the finite element method and ALTAIR software.

The energy synergistic mechanism of coaxial heterogeneous-wavelength hybrid laser beam and its effect on welding molten pool dynamics for aluminum alloy

The coaxial heterogeneous-wavelength hybrid laser beam (HW-HLB) heat source featuring a “Gauss + Flat top” energy distribution, which integrates the 1080 nm and 915 nm laser beam, was employed in this paper to achieve excellent stability in the welding of aluminum alloy. The interaction mechanism between aluminum alloy and laser beams with different wavelengths was taken as a point cut to explore the synergistic enhancement mechanism of coaxial HW-HLB . A thermal-fluid coupling model for HW-HLB welding, considering the synergistic effect of dual lasers, was established according to the welding experiment results. The influence of fiber laser power (PF) and diode laser power (PD) on the molten pool flow behavior during welding process was investigated. The dynamic of the molten pool and the maintenance mechanism of the keyhole were elucidated through in-situ monitoring experiments and thermal-flow simulations. The results indicated that, in contrast to the single fiber laser beam (FLB), the power density of HW-HLB presents a significant increase, which results in the “avalanche-like” augmentation of the plasma plume, as well as deeper depth of the keyhole. The energy synergistic enhancement effect of coaxial HW-HLB with PF=2800 W and PD=2500 W performs stronger and thorough changes in the morphology and flow behavior of the molten pool. The introduction of 915 nm laser beam improves the multi-reflection behavior in the inner keyhole. The findings of our research provide a theoretical framework for improving the stability of the laser weld molten pool and the quality of welds in aluminum alloys through the implementation of HW-HLB.

Research on Process Characteristics and Properties in Deep-Penetration Variable-Polarity Tungsten Inert Gas Welding of AA7075 Aluminum Alloy

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove.

Microstructure and mechanical properties of 7075 aluminum alloy welds by gas tungsten arc welding with trailing ultrasonic rotating extrusion

In this investigation, gas tungsten arc welding (GTAW) and gas tungsten arc welding with trailing ultrasonic rotating extrusion (U-RE-GTAW) were applied to 7075 aluminum alloys. Qualitative comparisons and analyses were carried out to investigate the effects of the ultrasonic rotary extrusion-assisted technology on GTAW processes. The weld joints fabricated by GTAW and U-RE-GTAW were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) techniques. Concurrently, the tensile strength and fatigue characteristics were assessed at ambient temperature. The experimental outcomes indicated that the U-RE-GTAW process mitigated porosity within the weld region and substantially augmented dislocation density, while concurrently achieving a notable reduction in grain size and an increase in the volume fraction of secondary phases due to the synergistic effects of ultrasonic oscillation and rotational extrusion. The enhancement in tensile and fatigue resistance of the welded joint was attributed to the strengthening mechanisms associated with these microstructural alterations. Specifically, the ultimate tensile strength exhibited a 20.4% increase, and the elongation at break was elevated by 46.3%. At stress amplitudes of 190 MPa, 160 MPa, and 100 MPa, the fatigue strength of the welded joints was enhanced by 67%, 55%, and 32%, respectively. A quantitative analysis was conducted to elucidate the impact of diverse strengthening mechanisms on the welded joints. It was concluded that dislocation strengthening is the predominant factor contributing to the superior performance of the U-RE-GTAW specimens.

Benchmarking wire-fed and autogenous laser beam welding to study the effect of Cu additions on weld integrity of 6060-T6 aluminium extrusion

In the automotive industry 6xxx aluminium alloys are preferred materials, yet their fabrication contributes to a considerable carbon footprint. A promising strategy to mitigate the environmental impact is the increased utilisation of recycled (secondary) aluminium, sourced from diverse scrap streams. However, as aluminium scraps come from different sources, the intrinsic variability of chemical composition, stemming from uncontrollable levels, poses a challenge, impacting material properties and weldability. Balancing manufacturability while enhancing the adoption of recycled alloys becomes a critical effort. This study aims at benchmarking wire-fed and autogenous laser beam welding to study the effect of Cu inclusions on weld integrity of 6060-T6 extrusion. The paper contributes to show the impact of Cu addition during laser welding of 6060-T6 aluminium alloys. Findings highlighted that the modification of chemical composition using filler wires is currently the most efficient approach to improve joint strength, although the Cu additions tend to reduce the weld strength.