Search

Wire Arc Additive Manufacturing (WAMM) consists in the manufacture of metallic preforms from the deposition of multilayer weld beads on a substrate, that is, from a three-dimensional model, the object is divided into layers defining the trajectories in which the addition of metal will be made, with the use of a robotic manipulator. The objective of this work is to study the influence of the addition of cold wire and the effect of interlayer temperature in the WAAM process, comparing it with the deposition made with a single wire, observing mechanical properties such as tensile strength, hardness, in addition to the cooling time for different interlayer temperatures and the geometry of the manufactured parts. A GMAW (Gas Metal Arc Welding) system was used coupled to a robotic manipulator, with multiple wires of 1.6 mm in diameter for the energized wire and 1.0 mm for the cold wire, both classified as ER70S-6. In order to manufacture the specimens for the tensile test, 20 layers were superimposed in a straight line, forming a wall, varying the interlayer temperature between each layer, using 100°C, 150°C and directly, with no waiting interval between layers. In general, a shorter cooling time was observed for the walls manufactured with the addition of cold wire when compared to depositions with a single wire. In addition, it was noted that the cold wire also influences the height and thickness of the pieces. In the mechanical tests, the cold wire did not significantly influence the hardness values. The highest values were found in the 100°C samples. For the tensile tests, it was observed that, in general, the addition of cold wire tended to increase the maximum tensile strength of the samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Porosity reduction in WAAM 5356 aluminum alloy, without adding any extra equipment, using the pulsed-AC metal transfer mode. • The main cause of the porosity in aluminum alloys is the trapped hydrogen that creates small and spherical pores. • The micropores are mainly located in the contour parts of the walls. • Micropore bands formed with small and spherical pores are observed at the inter-layer boundaries. • The porosity levels are lower in the double-bead walls than in the single-bead walls. The interest in aluminum-magnesium alloy additive manufacturing through Wire-arc Directed Energy Deposition (DED) technology has substantially grown in recent years. The main challenge in additive manufactured aluminum-magnesium alloys is the occurrence of porosity. In this context, Gas Metal Arc Welding (GMAW) based additive technology is suitable for aluminum printing as it allows high deposition rates and reduces porosity levels through alternative metal transfer modes without adding any extra equipment. Therefore, this research explores the effects of these alternative metal transfer modes, which determine the current signal shape and polarity, on the distribution and morphology of micropores using X-ray computed tomography in both single-bead and double-bead walls. The novelty of this paper lies in the comparison of the porosity obtained using alternative transfer modes, which, unlike CMT (Cold Metal Transfer) modes, have not been exhaustively analyzed. Additionally, to date, there has been no comprehensive comparison of the porosity results obtained in single walls and overlapped walls. The results demonstrate that pulsed-AC transfer mode with a current signal featuring variable polarity yields acceptable porosity fraction values of less than 0.04% in single-bead walls and less than 0.01% in double-bead walls, achieving high productivity. [ABSTRACT FROM AUTHOR]

This article presents a numerical sequential approach to predict the geometry of the weld line, the heat transfer, the dimension of the heat-affected zone, and the stress-strain fields in automated gas metal arc welding (GMAW). The integrated simulation approach has been implemented by using commercial software tools, and it has been applied to simulate nine welding cases study. The achieved outcomes have been compared to the measurements and the microscope observations of weldings produced experimentally, in order to validate the prediction capability of the model with respect to the filler material deposition, the heat-affected zone size, and the distortion of the welded materials. [ABSTRACT FROM AUTHOR]

The digitization of manufacturing processes enables promising applications for machine learning-assisted quality assurance. A widely used manufacturing process that can strongly benefit from data-driven solutions is gas metal arc welding (GMAW). The welding process is characterized by complex cause-effect relationships between material properties, process conditions and weld quality. In non-laboratory environments with frequently changing process parameters, accurate determination of weld quality by destructive testing is economically unfeasible. Deep learning offers the potential to identify the relationships in available process data and predict the weld quality from process observations. In this paper, we present a concept for a deep learning based predictive quality system in GMAW. At its core, the concept involves a pipeline consisting of four major phases: collection and management of multi-sensor data (e.g. current and voltage), real-time processing and feature engineering of the time series data by means of autoencoders, training and deployment of suitable recurrent deep learning models for quality predictions, and model evolutions under changing process conditions using continual learning. The concept provides the foundation for future research activities in which we will realize an online predictive quality system for running production. [ABSTRACT FROM AUTHOR]

• Long-term experiments to test atmospheric corrosion of hybrid metal structures. • Study of dissimilar welds between high-strength carbon steel and duplex stainless steel. • Investigation of different corrosion mechanisms through corrosion rate, morphology, and electrochemical tests. • Development of a corrosion database specifically for mildly corrosive environments to improve precition models. • Contribution to the ISO 9223:2012 standard through calibration and comparison of corrosion prediction model. This paper investigates the corrosion behaviour of dissimilar T-joints made of duplex stainless steel and carbon steel under atmospheric environments. Stainless steel grade EN1.4062 was welded to two different carbon steel grades, S355J2 and P460NL2, via gas metal arc welding to form T-joints. The fabricated specimens were subjected to 12-month exposure tests in four mildly corrosive environments distributed across 3 different European countries: Belgium, England, and Portugal. Uniform, galvanic, and pitting corrosion was observed and analysed in detail. In particular, the CS plates, nearby HAZs, and junctions between the SS and CS plates are areas with relatively low corrosion resistance. This finding provides guidance for the use of protective coating systems for dissimilar weldments. The evaluation of corrosion rates obtained in this study and from previous literature suggests that some prediction models are too conservative for atmospheric corrosion under mildly corrosive environments. Two mathematical functions for corrosion rate prediction have thus been recalibrated from a newly formulated corrosion database. A model with the best accuracy for carbon steel under similar conditions is finally identified. [ABSTRACT FROM AUTHOR]

The aluminum (Al) alloy double-wire pulsed gas metal arc welding (GMAW) has severe double arc interference issues. To reduce double arc interference, the advantages of double-wire pulsed GMAW and variable-polarity (VP) welding are combined to form Al alloy double-wire VP double base pulsed GMAW. The profile and behavioral characteristics of double arcs are analyzed using high-speed images to assess their physical properties. The arc load characteristics are explored through U - I curves, and the polarity switching process is analyzed from the perspective of double arc coupling. The experimental results showed that arcs with identical polarity are attracted to each other, while arcs with the opposite polarity repel each other. The coupling areas of two arcs with different polarities are therefore different; the electrode positive (EP) arc has a broader profile, while the electrode negative (EN) arc has an elongated profile. The stability of the leading arc is also affected by the polarity switching of the trailing arc. During the EN phase, the trailing arc can climb up to 2–3 times the wire diameter along the wire to search for metal oxide. The EN arc is more stable than the EP arc, and the EN peak arc has a load impedance that is 0.4–0.6 times lower than that of the EP peak arc. The polarity switching from EP to EN is easier due to the larger arc coupling area while switching from EN to EP is more difficult because of the thin arc coupling area. Regardless of polarity, the arc coupling area can provide charged particles for the arc to a certain extent and reduce the probability of arc extinguishing due to polarity switching. • To reduce double arc interference, the process of Al double-wire variable polarity (VP) double base pulsed GMAW are proposed. • The arc behavioral characteristics in double-wire VP double base pulsed GMAW are discussed based on the high-speed profile. • The law of arc load characteristics in the process are analyzed based on the U - I curves. • The polarity switching process are analyzed in terms of the double arc coupling phenomenon. [ABSTRACT FROM AUTHOR]

To understand the influence mechanism of post weld heat treatment (PWHT) on the strength and toughness of the deposited metal in ultra-high strength steel welding, gas metal arc welding (GMAW) was employed on the deposited metal, followed by testing and analysis of its microstructure and properties. The results indicate that the as-welded deposited metal consists of martensite and 3 % residual austenite, exhibiting significant dendritic micro-segregation. The segregation zone primarily comprises fine martensite and residual austenite. Following PWHT, the martensite in the deposited metal transforms into tempered martensite, and the residual austenite content decreases to 0.2 %, accompanied by the precipitation of a substantial amount of MoWC 2. The yield strength and average impact energy at room temperature for the deposited metal in the as-welded condition are measured at 1090 MPa and 46.67 J, respectively. After PWHT, these values increase to 1330 MPa and decrease to 32.33 J, respectively. Furthermore, the particles within the dimples of shear zone of the deposited metal impact fracture in the as-welded condition and the PWHT condition are identified as residual austenite and MoWC 2 , respectively. Based on four strengthening mechanisms, the calculated yield strength of the deposited metal aligns closely with the measured values. The primary strengthening mechanisms for deposited metal in the as-welded condition include fine crystal strengthening and dislocation strengthening, while those for deposited metal in the PWHT condition encompass fine crystal strengthening, dislocation strengthening, and second phase strengthening. [ABSTRACT FROM AUTHOR]

The present study investigates the precipitation behavior of Ti–Nb and Ti–Nb–V grade of advanced high strength ferrite-bainite steels in Heat Affected Zones (HAZ) during arc welding process. These micro-alloyed (Nb, Ti, V) steels have numerous precipitates in form of nitrides, carbides and carbonitrides typically: TiN, (Ti, Nb) (C, N) and (Ti, V, Nb) (C, N). Welding of these steels destroys the base microstructure and leads to softening of the HAZ. The reasons are phase transformations and dissolution of precipitates/re-precipitation and/or coarsening of some of the existing precipitates. This affects the mechanical properties e.g., deterioration of ultimate tensile strength (UTS) and reduction in hardness. The current paper highlights the microstructural and precipitation evolution in HAZ of both the grades and discusses in detail the effects of the microalloying on them. The present study uses characterization techniques such as Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Electron Back Scattered Diffraction (EBSD) to find out the phase evolution and the composition, morphology, size, and distribution of precipitates. Subsequently, simulation packages such as Thermo-calc and JMatPro are used to correlate these with the thermodynamic and kinetic predictions. [Display omitted] • Gas metal arc welding for two ferrite bainite (Ti–Nb and Ti–Nb–V) steels. • Microstructure evaluation using scanning and transmission electron microscopy. • Precipitation behavior studied in different heat-affected zones due to welding. • Equilibrium and kinetic calculations using Thermocalc and JMatPro softwares. [ABSTRACT FROM AUTHOR]

• A real-time torch posture detection method based on multiple magnetron sensing. • A mathematical model of multi-pole magnetron GTAW arc sensing. • A model of accurately extracting arc pressure feature points based on a support vector machine. 3D welds are prevalent in advanced manufacturing sectors such as pressure vessels, nuclear power construction, and aerospace. However, these industries employ colored metals with highly reflective surfaces and utilize Tungsten Inert Gas Shielded Arc Welding (GTAW), necessitating precise welding gun positioning. The complexity of 3D welds significantly burdens offline programming and teaching. Besides, traditional laser vision sensors prove ineffective due to substantial reflections from the workpiece surfaces. At present, no method exists for high-precision, real-time 3D weld path pose extraction. To solve these problems, we propose a real-time extraction method for 3D weld path poses using multi-pole magnetic-controlled GTAW arc sensing. Firstly, a corresponding mathematical model is developed to facilitate this process. Then, a precise method based on Support Vector Regression (SVR) for extracting arc pressure information is proposed to counter the interference from random noise in arc signals during feature point extraction from weld poses. Through a real-time extraction algorithm for 3D weld path postures based on multipole magnetron GTAW arc sensing. Finally, experimental real-time extractions on various typical workpieces demonstrate that the average extraction error is within 1°, with a maximum error not exceeding 2°. The results demonstrate the effectiveness of the proposed method under the intricate conditions associated with the GTAW process. [ABSTRACT FROM AUTHOR]

In this study, the performance of the automatic gas metal arc welding (GMAW) process in vacuum for similar and dissimilar joints of A353 and A516 steel plates with different thicknesses was intensively evaluated. Fracture of all vacuum-welded samples occurred in the heat-affected zone (HAZ) of A516 steel, highlighting the significant influence of HAZ microstructure and width on the cryogenic impact energy and strength of these joints. According to microscopic observations and impact tests, the fractures were fully ductile for notches in the weld and A353 HAZ, where dimples were observed on the fracture surfaces and the impact energy exceeded 50 J. This ductile behavior is particularly significant for notches in the weld due to the presence of a vacuum during welding prevents the formation of gas voids and oxide and hydride compounds that are normally the origin of cracks. However, for notches in the A516 HAZ, where the cleavage faces were observed on the fracture surfaces and the impact energy was less than 30 J, the fractures were quite brittle. For dissimilar vacuum-welded samples, the impact energy and fracture type for notches in the weld and A353 HAZ were nearly the same as those in similar A353 joints. However, for notches in the A516 HAZ, the impact energy and fracture type were close to those observed in the A516 joints. Yield strength and ultimate tensile strength (UTS) of A353-A353 non-vacuum-welded samples compared to vacuum-welded samples decreased by more than 78 % and 40 %, respectively. As well as, yield strengths and UTSs of A516-A516 non-vacuum samples compared to vacuum samples decreased by more than 34 % and 4 %, respectively. On the other side, the impact samples with a notch position in the weld suffered brittle fracture instead of ductile fracture because their impact energy decreased by about 40 %. • Preventing harmful oxide and hydride compounds, especially CrH and Cr 8 O 21 in the vacuum weld structure. • The tensile strength of vacuum-welded samples is higher than the non-vacuum-welded samples. • Fracture of vacuum and non-vacuum welded tensile samples in HAZ and Weld, respectively. • Minimum impact energy for A516 steel samples with notch position in the HAZ due to banding structure. [ABSTRACT FROM AUTHOR]

This article was focused on studying the influence of microstructure and impact performance of Q450NQR1 weathering steel welded joints using low-frequency mechanical vibrations during the welding process (GMAW). The analysis of the molten pool cooling and solidification process in vibration welding is conducted using a one-dimensional Stefan problem and the wave equation coupled model The computational results show that the molten pool cooling time decreases and the stress on the dendrites increases during the crystallization process as vibration frequency increase. Mechanical vibrations with a fixed amplitude of 0.1 mm and frequencies of 0, 20, 40, and 60 Hz were applied to the welding molten pool under the same welding parameters. The microstructure of the weld joints was examined using metallurgical microscope. Charpy impact test was used to measure the impact properties. The results show that the increase in weld zone width is accompanied by a reduction in the heat-affected zone width after the application of mechanical vibrations. The primary proeutectoid ferrite dendrites undergo fragmentation. The acicular ferrite content has increased and structural refinement. The impact energy in the weld zone increases with the increase in vibration frequency. The welded joints exhibit enhanced toughness, with an increased proportion of the fibrous region (F) and the shear lip region (S) at the fracture surface. The distance between the crack instability position and the root of the notch increases. • The microstructure, impact properties. • Stefan problem and the wave equation. • Grain refinement, impact energy increase. [ABSTRACT FROM AUTHOR]

Gas Metal Arc Welding (GMAW) is a critical process in manufacturing, known for its efficiency and versatility. The double-electrode GMAW (DE-GMAW) technique further enhances these attributes, offering superior welding speed and improved melting effects. However, controlling the DE-GMAW process effectively remains a complex challenge due to the nonlinear and dynamic nature of the system. The process involves intricate interactions between electrical, thermal, and mechanical phenomena, resulting in highly nonlinear behavior. Variations in material properties, environmental conditions, and external disturbances can adversely affect the welding process. Moreover, traditional control methods often fail to account for unmodeled dynamics and modeling errors, leading to performance degradation and potential instability. To address these challenges, this paper introduces a robust adaptive control scheme tailored for DE-GMAW systems, which combines online projection estimation identification and pole placement strategy at the same time to compensate for parameter uncertainties, external disturbances, and unmodeled dynamics. Simulation examples in welding process are carried out to demonstrate the effectiveness of the proposed robust adaptive control scheme. • A double-input double-output for the DE-GMAW system is put forward to consider the HM and the nonlinearity effects firstly, thereby better reflecting the engineering requirements. • A novel robust adaptive control combining pole assign self-tuning control and online projection estimation is first employed to deal with the modeling error of the nonlinear DE-GMAW. • Sufficient conditions are developed to demonstrate the nonlinear closed-loop system is bounded-input bounded-output stable. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal annealing temperatures for GMAWed CoCrFeMnNi joints with 410 stainless filler were determined through high-throughput thermodynamic calculations. • BM and HAZ phases match model predictions, slight FZ deviations observed. • FZ precipitates had no detrimental effect on joint mechanical properties. • PWHT boosts joint plasticity by ≈7 sevenfold (43.1 % vs. 6.4 %) while maintaining strength (587 vs. 641 MPa). • Tensile failure shifts from weld toe to BM zone after annealing. Post-weld annealing is a promising method for enhancing the performance of welded joints. However, traditional trial-and-error approaches are often time-consuming and inefficient, limiting their application in industrial production. To overcome this challenge, this study integrates high-throughput thermodynamic simulation techniques with a custom Python script to rapidly screen annealing temperatures for GMAWed CoCrFeMnNi high entropy alloy welded joints with ERNiMo-410 filler wire. By employing a combination of microstructural characterizations (such as Electron Backscatter Diffraction (EBSD) and Synchrotron X-ray Diffraction (SXRD)) and mechanical testing (including hardness testing and tensile Digital Image Correlation (DIC) analysis), the study validates the effects of selected annealing temperatures on the microstructure evolution and mechanical behavior of the welded joints. The results demonstrate that the optimized annealing temperature significantly enhances the uniformity of the microstructure and increases elongation at fracture by approximately sevenfold to 43.1 %, while maintaining comparable yield and ultimate strengths. This study highlights the potential industrial value of this method, offering an efficient and scientific approach for optimizing welded joint performance. [ABSTRACT FROM AUTHOR]

The efficient gas metal arc welding (GMAW) of thick-plate titanium alloys contributes to the application and promotion of large titanium alloy structural parts. However, the severe embrittlement behavior in the heat-affected zone (HAZ) seriously harms the service performance. In the current work, the microstructure evolution and tensile properties in HAZ are systematically analyzed by employing the thermal-mechanical simulation tests, and the embrittlement mechanism is innovatively elucidated for the first time by discussing the resistance and impetus to dislocation slip. The results showed that as it got closer to weld metal, the α phase underwent the transformation of "α p + α s →α p +α'→ghost α+α'→α' + α GB ". Furthermore, the resistance to dislocation slip increased gradually due to the more severe lattice distortion, the higher density of high-angle grain boundaries (HAGBs), and the more intensive strain concentration, while the impetus decreased gradually due to the reduced Schmid factor (SF) of {0001}<11 2 ̅ 0> slip system. These led to the most severe embrittlement behavior occurring at the near-weld metal. The current work provides a valuable theoretical guide for welding quality optimization of large titanium alloy structural parts. [Display omitted] • Embrittlement mechanism in HAZ of GMAWed titanium alloys is first elucidated. • Morphology and texture of high-temperature β are observed by parent β reconstruction. • Worst embrittlement occurs at near-weld metal due to α', αGB, and coarse prior-β. • Relation between microstructure and embrittlement is established by dislocation slip. [ABSTRACT FROM AUTHOR]

This study investigates wire arc additive manufacturing (WAAM) also known as wire-arc directed energy deposition (WA-DED) of type 430 ferritic stainless steel, with a focus on the microstructural characteristics and mechanical behavior of the printed component. The WAAM system utilized a gas metal arc welding (GMAW)-based approach to produce a single-track multi-layer component. Microstructural analysis was conducted using a dual approach, combining Thermo-Calc/JMatPro calculations for theoretical insights, and light optical microscopy, field-emission scanning electron microscopy (FESEM), and electron backscatter diffraction (EBSD) for experimental investigations. The microstructure of WAAM-printed 430 steel is characterized by the formation of large columnar α-ferrite grains decorated with fine intragranular Cr-rich carbides, grain boundary martensite, and the formation of a precipitation-free zone (PFZ) near the martensite layer. These microstructural features of WAAM-printed 430 steel resulted in deficiencies in ultimate tensile strength and ductility, compared to wrought AISI 430 steel. The study highlights the need for implementing an effective strategy for grain refining and designing a tailored post-build heat treatment to enhance the strength and ductility of the printed 430 ferritic stainless steel. • Examined metallurgical challenges in WAAM of 430 ferritic stainless steel. • WAAM-printed 430 steel features large columnar ferrite grains with fine chromium-rich carbides and GB martensite. • Low ductility is linked to columnar grains and martensite presence. • Potential improvements include grain refinement, reduced martensite formation, and tailored post-build heat treatment. [ABSTRACT FROM AUTHOR]

Hindrance to weld metal shrinkage by the adjacent base material introduces inevitable residual stress and distortion in welded components. Nevertheless, proper choice of welding process can reduce the magnitude of tensile residual stress and distortion. Here hybrid laser MIG and Hotwire-TIG welding processes are used, which provides sound 316L(N) stainless-steel weld joint at reduced heat input. The numerical modeling and experimental result shows that tensile residual stress distribution is substantially narrower in hybrid laser MIG than in Hotwire-TIG weld joint. Furthermore, the degree of external restraint significantly influences the magnitude of residual stress distribution and distortion. The numerical and experimental results exhibited reasonable agreement. [Display omitted] • 11 mm thick Type 316L(N) weld joints were fabricated using HLM and HW-TIG welding techniques. • The IHM and MHM accurately predicted residual stress and distortion in HLM and HW-TIG weld joints. • Residual stress distribution was narrower in HLM (∼22 mm) than HW-TIG weld joint (∼46 mm). [ABSTRACT FROM AUTHOR]

The electrochemical behaviour of the passive film formed over the surface of dissimilar welds of AISI 2205 duplex stainless steel and AISI 316L austenitic stainless steel was evaluated using electrochemical impedance spectroscopy (EIS). Gas metal arc welding (GMAW) of the plates, 6.35 mm thick, was performed using ER309L and ER316L-Si filler wires with pulsed (GMAW-P) and spray (GMAW-S) transfer modes. The passive film resistance was determined conducting EIS tests at different anodic overpotentials (0.05, 0.150, 0.250 and 0.375 V). The results showed that increasing the anodic overpotential up to 0.250 V, led to the formation of a thicker, continuous and stable passive layer. • GMAW was performed using ER309L and ER316L-Si with pulsed and spray transfer modes. • Irrespective of electrode and transfer mode, anodic overpotential up to 0.250 V yielded a stable passive layer. • Bode diagrams showed higher stability of the passive layer for the GMAW-P 2205/316L dissimilar welds. • Optical microscopy disclosed better microstructural features for the ER309L filler wire with GMAW-P. [ABSTRACT FROM AUTHOR]

[Display omitted] Carbon nanotubes (CNT)-reinforced metal matrix nanocomposites balance toughness and ductility and, therefore, can reduce maintenance costs of industrial equipment. In this sense, flux-cored made of low carbon steel filled with CNT/Ti6Al4V/CaF 2 were used as filler metal to coat an A131 grade A steel sheet via GTAW process. SEM and Raman spectroscopy analyses evidence the partial phase transformation between Ti and CNT in TiC-CNT precipitates, which can act as barriers to dislocation movements in a ferritic matrix. Consequently, the hardnesses of the coatings were up to 33.9–77.4 % higher than the base metal. Therefore, incorporating TiC-CNT precipitate-based reinforcements via arc welding can improve the hardness of conventional steels. [ABSTRACT FROM AUTHOR]

• The process parameters are determined through trial runs based on the bead height and width of single-bead geometry. • The grain boundary wetting transion (GBWT) is depicted by SEM image to identify incomplete and complete wetting transition. • A precipitation-hardened matrix has formed, resulting in reduced ductility in the top portion of the deposited sample. • The laves and δ phases of the deposited samples are investigated by SEM analysis, and the EBSD γ phase is identified. • The grain growth occurs when Ni elements are added to the laves and delta phases of the deposited samples. The current research work deals with the investigation of mechanical, wetting transition on grain boundary (GB) and metallurgical properties of Inconel 718 alloy used in aerospace industrial applications. The fabrication of thin-wall structure (multilayer structure) is fabricated using wire arc additive manufacturing (WAAM) technique. The novelty of this method is that gas metal arc welding (GMAW) is used as energy source and cold metal transfer (CMT) is used as mode of droplet transfer. Four tensile samples are extracted asper ASTM E8/E8M standards and three microstructure samples are extracted from thin wall structure. Optical microscopy (OM), SEM, EDAX, and EBSD analysis were carried out. In addition, Hardness and tensile tests, as well as fractography analysis were conducted. The grain boundary wetting transition (GBWT) analysis is also carried out. SEM analysis reveals that Nb-rich MC-type carbide contains grain boundaries of droplets, indicating incomplete wetting. Laves and delta (δ) phases are also identified as liquids of a continuous layer separated by Ni elements, indicating complete wetting. EBSD analysis indicates the average grain size as 251.2 μm. The average value of micro hardness as 417.3 HV and UTS as 609.75 MPa are achieved. [ABSTRACT FROM AUTHOR]

Double-sided symmetric MIG welding can significantly enhance welding efficiency for thick titanium alloys and holds promising engineering applications. However, the use of high currents and deposition rates in this process not only boosts welding efficiency but also impacts joint performance, particularly its impact toughness. In this study, the Charpy impact performance of double-sided double-arc MIG welded joints in each region was studied via oscillometric impact tests, and the main factors affecting the impact of joints were revealed. Scanning electron microscope was used to observe the fractures, and the microstructure characteristics and grain orientation of the impact crack propagation path were observed and analysed via metallurgical microscopy and EBSD. In addition, the microstructure of each region of the joint was observed via metallographic microscopy and transmission electron microscopy, which revealed the microstructure characteristics of different regions of the joint and clarified the effects of microstructure and grain orientation in different regions of the welded joint on the impact performance of each region of the double-sided, double-arc MIG welded joint. The results show that the crack initiation energy across different regions of joints typically ranges between 18 and 20 J, with minimal variations. Crack propagation plays a pivotal role in determining impact toughness, which is influenced both by microstructural features and orientation. This provides guidance for subsequent adjustments and improvements to the impact performance of the joint. • For the first time, the impact toughness of efficient double-sided double-arc MIG welding joints in titanium alloy applications was studied across different regions such as the weld metal, fusion line, and heat-affected zone, as well as different positions in the upper, middle, and lower sections of the welding joint. • By combining the analysis of microstructural transformations and orientation during the welding process, the study aims to elucidate the key factors influencing the impact performance of the joints. [ABSTRACT FROM AUTHOR]

• Behavior of corroded Q890 and Q960 ultra-high strength steels as well as weld metals made of ER100S-G, ER110S-G, ER120S-G feedstock wires was investigated. • Tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. • Geometric profiles of corroded steel specimens were determined via 3D laser scanning. • Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are discussed. • Accurate prediction equations were proposed to determine the residual mechanical properties of corroded ultra-high strength steels and weld metals. This paper presents an in-depth investigation into the residual mechanical properties of ultra-high-strength steels and weld metals after exposure to corrosive environment. The tensile specimens of weld metals were fabricated using ER100S-G, ER110S-G, ER120S-G feedstock wires by robotic gas metal arc welding, whilst ultra-high-strength steel tensile coupon specimens were machined from the Q890 and Q960 steel plates. The high-strength steel and weld metal tensile specimens were exposed to neutral salt spray accelerated corrosion conditions. Six exposure durations were designed to achieve different corrosion degrees of specimens. A total of 23 corroded ultra-high-strength steel tensile coupon specimens and 19 corroded high-strength weld metal specimens were included. The geometric profiles of corroded steel specimens were determined via non-contact 3D laser scanning. Monotonic tensile tests were conducted to determine the stress-strain responses and key mechanical properties of corroded steel and weld specimens. Mechanical properties deterioration of corroded ultra-high-strength steels and weld metals are reported and discussed. Prediction equations on the residual mechanical properties regarding the tensile loading capacity, yield stress and ultimate tensile stress of ultra-high-strength steels and weld metals after exposure to corrosive environment were established. [ABSTRACT FROM AUTHOR]

The demand for high-strength steels has continued to increase in various fields of industry due to the advancement in technology. The wire arc additive manufacturing (WAAM) enables the fabrication of high-strength structures from different materials by controlling the raw wire in layers. This study focuses on the fabrication of high-strength steel by WAAM using the gas metal arc welding + cold wire feeding (GMAW + CWF) technique. A new alloy was formed by simultaneously adding 316LSi stainless steel from the CWF to the low alloyed ER70S-6 steel from the GMAW torch. In this way, three different new alloyed structures were produced with varied 316LSi ratios ranging from 10 %, 20 % and 25 % respectively. Besides, their metallurgical and mechanical properties were compared with each other and with single material WAAMed structures. In the macrostructure examinations, no defects due to the mixture of both materials were found and both materials melted properly to create the new alloy. Due to the alloying elements transferred from 316LSi, the microstructure of the new material parts were completely changed compared to the single material WAAMed components and bainite and martensite phases were found in the new alloys. The hardness increased significantly compared to the single-material WAAMed structures and increased up to 139 % and 84 % compared to the single-material WAAMed ER70S-6 and 316LSi, respectively. The tensile strength showed a great improvement and reached almost 1200 MPa, increased by 142 % compared to the single-material WAAMed structure. The fabricated new alloys have the potential to be a candidate material for industries that use high-strength steel. • GMAW + cold wire feeding approach was implemented in the WAAM process. • New alloy parts were successfully fabricated from different two wires. • The tensile strength of the new alloys reached almost 1200 MPa. [ABSTRACT FROM AUTHOR]

This study explores the fabrication of a trimetallic functionally graded material (FGM) using stainless steel (ER316L), duplex steel (ER2205), and Inconel 718 (IN718) through a gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) process. The metallurgical examination reveals the large columnar austenitic grains and δ-ferrite phase at the grain boundaries along the built direction in the stainless-steel zone. At the interface of ER2205-IN718, a distinct boundary is observed due to the different alloy compositions. Scanning electron microscopy (SEM) shows metal carbide of nickel (Ni), molybdenum (Mo), and niobium (Nb) along the grain boundaries and nodular-shaped Lave phases in the IN718 zone. The energy dispersive spectroscopy (EDS) analysis reveals a gradual variation of Ni and Fe content, indicating the successful fabrication of the FGM. The mechanical characterization reveals that the hardness of the developed FGM steadily increases from bottom to top. However, at the ER2205-IN718 interface, it experiences a sharp decrease, followed by a subsequent increase within the IN718 zone. The tensile test demonstrated an increase in tensile strength along the built direction, accompanied by a reduction in strain. Notably, the minimum strain observed in the developed FGM is approximately equal to that of IN718 alloy. [Display omitted] • A tri-metallic functionally graded material is developed by GMAW-WAAM process. • Large columnar austenitic grains and δ-ferrite phase are present in ER316L. • The distinct boundaries at alloy interfaces with metal carbides and nodular-shaped Laves phases are present in IN718. • The FGM exhibits an improved tensile strength and microhardness along the built direction. [ABSTRACT FROM AUTHOR]

This work aims to combine different numerical models already used in the literature and to develop a new application to predict the thermal gradient generated by GMAW welding in a T-joint. This more comprehensive approach improves the computational processing time of the model while providing more accurate results for the fusion zone (FZ) and heat-affected zone (HAZ). The models were created using the Finite Element Method (FEM) with the commercial software ABAQUS. The first model represents welding through a volumetric heat flux, presented in this study as Goldak's double ellipsoid (GHF). The geometry and intensity of the flux were implemented in the software via the DFLUX subroutine. For the second model, the element birth and death method with prescribed weld temperature was used (PWT). Finally, the new model is created by combining the strengths of the previous ones (GHF+PWT). Furthermore, for the proposed new model, a comparison is made between different starting points for the volumetric heat flux, showing that there is a significant impact on the temperature gradient and processing time. The boundary conditions, represented by heat loss through convection and radiation, were implemented using the FILM subroutine. Both subroutines were programmed in FORTRAN. The temperature history from the numerical analyses was compared with experimental measurements taken with K-type thermocouples. In addition, macrographic tests were conducted to evaluate the dimensions of the weld bead. The results indicate that the proposed new model has a better agreement between the temperature distribution along the plate and the shape of the fusion zone, as well as an improvement in processing time. • Welding simulation using ABAQUS software involves programming subroutines to implement the heat source. • Various starting points for the heat flow are defined, along with their corresponding temperature responses on the board. • The work used numerical models to improve the thermal representation of the weld and reduce computational processing time. • The new model better represents the molten zone and has a computational time 49.50% less than the traditional numerical model. • Experimental tests were conducted to validate thermal analyses. [ABSTRACT FROM AUTHOR]

• A numerical model is established for rotating laser hybrid fillet welding with He-Ar shielding gas compositions. • Effects of rotating laser and He-Ar shielding gas compositions on arc physical properties are investigated. • With the He content increases, the arc temperature and distribution are more concentrated, the arc flow velocity and pressure decrease. • He-Ar shielding gas mixtures increase the arc heat flux density, suppress the shielding effect of laser-induced plume, and improve the weld penetration. To understand the influence mechanism of He-Ar shielding gas composition on arc physical properties in laser + GMAW hybrid welding, this study establishes an arc numerical analysis model in rotating laser + GMAW hybrid fillet welding by considering the geometric feature of joint configuration and the physical parameters of He-Ar shielding gas. The effects of He-Ar shielding gas mixtures in different ratios on arc plasma temperature, velocity, and pressure are investigated, respectively. The results show that with the increasing He content in the shielding gas, the overall shape of arc is compressed, the peak temperature decreases, the arc temperature distribution range is more concentrated, which is beneficial to increasing the weld penetration depth. The arc plasma flow velocity increases with the He content increases, but the plasma flow pattern becomes disordered when the He content reaches 50 %, which is not conducive to the stability of arc. The arc pressure value and the high-pressure distribution region near the workpiece surface increase significantly with an increasing He content ratio, due to the contraction effect of high He content mixed shielding gas on the arc. [ABSTRACT FROM AUTHOR]

An innovative twin-wire arc additive manufacturing (T-WAAM) has been deployed to fabricate a Co-rich non-equiatomic Co–Cr–Ni medium entropy alloy. The TWAAM-built single-wall structures of Co 50 Cr 10 Ni 40 alloy were fabricated under argon gas shielding using dual gas metal arc welding sources. The microstructure studies revealed a single-phase FCC crystal structure and defect-free deposition. The slender columnar substructure and cellular substructure are formed along the build direction (BD) and scan direction (SD) respectively, which are commonly observed in the wall structures of other conventional FCC alloys. The tensile coupon SD and BD displayed a superior high strength and ductility combination. The T-WAAM-fabricated Co 50 Cr 10 Ni 40 alloy showed both strength and elongation 1.4 times greater than that of the laser additive manufactured equiatomic CoCrNi wall structure. Thus, the study opens up a new avenue to tailor the mechanical properties of CoCrNi MEA by composition variation, with an added advantage of higher deposition rates of TWAAM. • Proposing a novel twin-wire arc additive manufacturing technique. • A novel, non-equiatomic CoCrNi alloy was developed and prepared. • Superior tensile properties of alloy are benefited from TWIP and Cr 2 O 3 nano precipitation. [ABSTRACT FROM AUTHOR]

• This study presents a quantitative measurement of the metal transfer frequency of a metal-cored wire under various argon-CO2 shielding gas mixtures (5, 10, 15, 20, 25,50, and 100%) and compares it with that of a solid wire. • Through shadowgraph observation and arc plasma investigation, the mechanism of the effect of CO2 concentration on the metal transfer of the metal-cored wire was proposed. • The metal transfer frequency of solid wire was monotonically decreased when CO 2 content increased, while that of the metal-cored wire reached a peak at a critical CO 2 concentration of 15%. • The equilibrium between arc attachment and the length of unmelted flux at the wire tip was found to influence droplet detachment behavior. Both factors were notably influenced by the CO 2 content, with equilibrium being attained at a CO 2 concentration of 15%. Metal transfer frequencies in a gas metal arc welding process with a metal-cored wire were quantitatively measured for the first time as a function of the CO 2 content (i.e., 5, 10, 15, 20, 25, 50, and 100%) in argon-CO 2 shielding gas mixtures at welding currents of 220, 250, and 280 A, and the results were compared with those of a solid wire. As a result, the metal transfer frequency of solid wire was monotonically decreased with the CO 2 content owing to an increase in the arc pressure, which prevented droplet detachment. However, the metal transfer frequency of the metal-cored wire presented a maximum value at 15% CO 2 under all the current levels. The transfer behavior was supposed to depend on the relation between the arc attachment position and the tip of the unmelted flux position inside the cored wire. When the CO 2 concentration was low, the arc was attached higher than the unmelted flux, causing the electromagnetic force to be ineffective in droplet separation. When the CO 2 concentration increased slightly, the arc was moved downward to the tip of the unmelted flux. That tendency temporarily facilitated the neck formation at the wire tip due to enhanced electromagnetic force flowing through the molten metal on the wire tip. Nevertheless, when the CO 2 content increased over a critical value, the arc pressure became a dominant factor to hinder the droplet detachment, which caused a decrease in transfer frequency. Consequently, the metal transfer frequency of metal-cored wire became maximum at 15% CO 2. [ABSTRACT FROM AUTHOR]

The trade-off between strength and toughness is a long-term challenge for engineering metal structural materials. However, natural materials overcome the inverse relationship between strength and toughness through their unique structures. Inspired by plant leaves and dragonfly wings, a 'soft-hard' alternating bionic heterostructure is prepared on 6061-T6 Al alloy MIG welded joints by laser surface remelting (LSR) technology. After LSR, the grain size of the laser treated zone is significantly refined, dislocation density is increased, and the formation of fine and stable GP zone and β′′ phase is promoted, enhancing microhardness and tensile properties of the LSRed sample. By adjusting the laser stripe spacing and distribution angle, stress transfer and redistribution can be optimized, effectively improving the tensile properties of the welded joint can be. Compared to as-welded sample, the tensile strength, yield strength and elongation of LSRed sample can be increased by 30.6 %, 13.6 % and 102 %, respectively. In addition, the bionic heterostructure composed of grain size gradient, dislocation gradient and precipitated phases gradient can effectively develop heterogeneous deformation induced (HDI) stress strengthening and HDI strain hardening, enabling synergistic strengthening of strength and toughness. • Laser surface remelting provides a new choice for the preparation of bionic heterostructure. • Bionic heterostructure are constructed on Al alloy welded joints. • Bionic heterostructure joint exhibits excellent strength-toughness matching. • High strength is attributed to fine grain, dislocation strengthening, precipitation strengthening and stress transfer. [ABSTRACT FROM AUTHOR]

Additive manufacturing is critical to repair, rebuild, and rapidly manufacture major components in today's manufacturing environment. Wire arc additive manufacturing technique using metal inert gas welding, which is a better way to produce large-scale parts at a subsidized cost was experimented on Incoloy 825 due to its many industrial applications in the construction of large structures. As bead deposition is vital for wire arc additive manufacturing, single bead depositions were performed. Metrological features of all deposited beads are evaluated using the CNC Video Measuring System by capturing the macrostructures. The effects of input parameters on bead geometry are statistically analyzed, and regression models are derived to forecast bead geometry. An adaptive Neural Fuzzy Inference System was implemented to predict geometrical characteristics, and the results were compared with experimental results. Subtractive clustering fuzzy inference model obtained the lowest percentage error difference in predicting deposited bead geometry as a function of process parameters. Further, the multi-objective optimization technique determined optimal input parameters for the best bead geometry. Finally, using identified optimum parameters, wire arc additive manufacturing of a single-pass multi-layer wall of Incoloy 825 was successfully constructed for validation, which revealed that the microstructure of the built structure was of appreciable quality without cracks and porosity. [Display omitted] • Wire arc additive manufacturing technique has experimented on Incoloy 825. • The metrological features of all deposited beads were studied. • A CNC Video Measuring System is used for the measurement of deposited bead geometry. • An adaptive neuro-fuzzy model is implemented for the prediction of bead geometry. • A multi-objective optimization technique was used to determine the optimal bead geometry parameters. [ABSTRACT FROM AUTHOR]

In the present study, functionally graded material (FGM) of Austenitic Stainless Steel-SS 316L and Nickel-based superalloy-Inconel 625 (IN625) was manufactured via Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM). WAAM processed FGM was well-formed without any defects and solidification cracking was not observed at the bi-metallic interface (IF) region. Microstructural features show a sharp transition at the IF with a discontinued dendritic structure. Energy-dispersive X-ray spectroscopy (EDS) examination confirmed the fine dissolution of elements at the IF and no major difference in the composition was observed. Electron Backscatter Diffraction (EBSD) maps confirmed that the grains are dominantly columnar while the IF revealed the smooth crystallographic growth along with large elongated dendrites in the< 001 >direction. The microstructure was mainly austenitic in the SS 316L layers with a lower fraction of ferrite while precipitates were noticed in the IN625 layers within the austenitic matrix. Yield strength (YS) and tensile strength (UTS) of SS 316L and IN625 were comparable with wrought ones. All the IF samples at 90° failed in the SS 316L region because of the lower UTS in comparison to IN625 and the mode of fracture was ductile. Microhardness measurements depicted the gradual change of hardness along the building direction. The present work highlights the potential of WAAM to fabricate FGM with required properties and is a viable manufacturing alternative to the traditional manufacturing techniques for producingFGM's. [Display omitted] [ABSTRACT FROM AUTHOR]

Naval grade, high strength low alloy (HSLA) steel is designed especially for shipbuilding applications due to its high strength to weight ratio. The conventional fusion welding processes of shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) are employed widely for structural applications. This work reports the influence of welding processes on mechanical properties and metallurgical characteristics of fusion welded DMR249A grade steel. The evaluating tensile, impact, microhardness properties were correlated with microstructures. The maximum recorded transverse tensile strength value of SMAW and GMAW joints were 558 MPa and 578 MPa. The lower microhardness had obtained in the subcritical heat-affected zone than other regions. The weld zone microstructure consists of fine, elongated, and columnar grain structures. From this investigation, it has been concluded that GMAW joints displayed marginally better properties than SMAW joints. But most weld failures has been observed in the subcritical heat-affected region; due to grain deformation and subsequent softening in the weldment. [ABSTRACT FROM AUTHOR]

In this study, Ultra-high Hard Armor (UHA) steel is welded with Rolled Homogenous Armor (RHA) steels using Gas Metal Arc Welding (GMAW) process with Austenitic Stainless Steel (ASS), Duplex Stainless Steel (DSS), and Low Hydrogen Ferritic (LHF) fillers. Ballistic resistance against Weld Metal (WM) is determined using 7.62 × 39 mm BALL projectile. Three new modes of failure were identified from the ballistic testing (i) Finer Wear Debris with Cleavage (FWDC) (ii) Coarser Wear Debris with Cleavage (CWDC) (iii) Cleavage failure (C), based on the fractured surface. All joints stopped the ball projectile at the weld metal region without perforation. However, the joint fabricated using ASS electrodes shows superior ballistic performance than other joints with Cleavage mode of failure (C) mainly due to the absence of wear debris. ASS weldment (5% Delta ferrite and 95% austenite) performs better in ballistic resistance because of the plastic deformation along with energy absorption properties of the austenite phase than DSS (69 Delta ferrite and 31% austenite) and LHF (100% ferrite). Migration of Chromium (Cr) from the weld metal to base metal results in an unmixed zone and martensitic band in the HAZ of ASS joint. [ABSTRACT FROM AUTHOR]

In the present study, Gas Metal Arc Welding (GMAW) is used to deposit AISI 304 stainless steel layer on the mild steel substrate. The cladding parameters like welding voltage and feed rate have been varied to identify the deposited AISI 304 stainless steel bead profile and factors affecting the bead deposition on the mild steel substrate. Microscopic and EDS analysis confirms the successful deposition of the stainless steel layer on the mild steel substrate. The GMAW parameters like welding voltage and wire feed rate (WFR) govern the AISI 304 clad bead quality like clad profile, heat affected zone (HAZ), and clad penetration. A numerical model has also been developed using a double ellipsoidal heat source to identify the effect of welding parameters on the clad bead. The developed numerical model identifies the temperature distribution along with the clad bead profile and the model is identical with the experimental results. The experimental results showed that a non-uniform weld bead formation has been observed at lower voltage (14 V) and low WFR (3 m/min). The clad bead quality has improved with an increase in the welding voltage (16 V & 18 V) and wire feed rate (5 m/min & 7 m/min). However, cladding at a high wire feed rate (7 m/min) results in low dilution of the clad material with the substrate. [ABSTRACT FROM AUTHOR]

In recent decades, Additive Manufacturing (AM) has become a viable alternative to the manufacture of metal parts. Wire arc additive manufacturing (WAAM), a welding-based AM technique is an important research area since it permits the economical manufacture of large-scale parts with relatively high deposition rates. This article compares the effect of heat input on mechanical properties of carbon steel cylindrical components fabricated by Gas Metal Arc Welding (GMAW) and Cold Metal Transferred Arc Welding (CMTAW) processes. Firstly, the influence of heat input on the grain size was analysed. Subsequently, the effect of heat input on the tensile properties, impact toughness and hardness of the cylindrical components were studied along the building direction. The cylindrical component made by CMTAW process showed superior tensile properties and higher impact toughness than GMAW component. Similarly, CMTAW component exhibited higher hardness than GMAW cylindrical component. The variations in mechanical properties are mainly due to the appreciable variations that have occurred in the microstructural features and different grain sizes evolved at different heat input levels. The bottom and top regions of the fractured tensile and impact specimens of the components are characterised by dimple structures revealing the ductile fracture. [ABSTRACT FROM AUTHOR]

Compared with the gas metal arc welding (GMAW), the cold metal transfer technology can significantly reduce the welding heat input owing to obtain the output current of almost zero in the droplet detaching, which has a greater advantage in additive manufacturing. In this work, the cold metal transfer was employed to study the law of appearance and mechanical behavior of additively manufacturing of Ti–6Al–4V alloy. The results showed that the continuous and uniform weld appearance could be obtained when the current of 120 A–130 A was used. In the top layer, middle layer and bottom layer of thin-walled components, the same microstructure was obtained with the different parameters, which were mainly consisted of the columnar original β grains and acicular martensite α'. The max-hardness was obtained in the bottom zone (BZ) of thin-walled component. With the increase of welding current, the hardness values in BZ were decreased. With the increases of current, the tensile strength was reduced, which caused by the grain growth. [ABSTRACT FROM AUTHOR]

• Nanomechanical characteristics of TIG, MIG, and diffusion bonded IN718/SS 316L were investigated. • Diffusion bonding is preferred over fusion as it reduces IMCs and carbides. • Diffusion bonding exhibits 11% and 7% lower hardness than MIG and TIG welding. • Maximum elastic modulus occurred in WZ of TIG and MIG while at the interface of diffusion bonding. The nanomechanical characteristics of Metal Inert Gas (MIG), Tungsten Inert Gas (TIG), and diffusion-bonded Inconel (IN718) and Austenitic Stainless Steel (SS 316L) were investigated. The nano hardness and elastic modulus of different weldments were evaluated using nanoindentation and compared. The results showed that intermetallic compounds (IMCs) and carbides were reduced with diffusion bonding. Moreover, maximum nano hardness and elastic modulus occurred in the welded zone (WZ) of TIG and MIG welded joints while at the bonding interface in diffusion bonding (DB). Lastly, the nano hardness of the bonding interface in diffusion-bonded was 11 % and 7 % lower compared to MIG and TIG welded joints. [ABSTRACT FROM AUTHOR]

In the European Union (EU), steel structures adhere to design and fabrication standards outlined in EN 1993 and EN 1090–2. The second sets technical requirements for executing steel and aluminum structures, referencing EN ISO 5817 for weld imperfections. This standard categorizes imperfections into three levels, with uncertainty surrounding their impact on load-bearing capacity. This article addresses this gap, presenting experimental data on the influence of undercut and axial misalignment on butt-welded joints welded using Gas Metal Arc Welding (GMAW) under static tension loading. It challenges existing quality limits in EN ISO 5817 and compares them with BS:7910 and Volvo standards. The study utilizes 3D scanning for imperfection characterization and conducts large-scale tension tests, revealing a correlation between undercut depth and load-bearing capacity. The impact of axial misalignment on load capacity is explored, indicating a minor influence. The findings contribute to establishing more realistic quality limits for welded structures, enhancing safety and efficiency in steel construction. • Study challenges weld imperfection limits in EN ISO 5817. • Focus on undercuts and axial misalignment in butt-welded joints. • 3D scanning used for precise imperfection assessment. • The results provide information on better quality limits for steel construction. [ABSTRACT FROM AUTHOR]

• It is feasible to perform manual GMAW-WAAM using high arc current. • Mechanical properties of 308L can be optimised in arc current range of 150A-170A. • A higher arc current than 190A tends to increase material brittleness. This study investigates the impact of high arc current on the mechanical properties and microstructure of thin-walled material fabricated using manual GMAW wire arc additive manufacturing (WAAM). The ER308L electrodes were used to fabricate samples using high currents of 150A, 170A, and 190A; voltages of 11 V, 11.5 V, and 12 V; and travel speeds of 400 mm/min, 435 mm/min, and 450 mm/min. It was found that increasing the current improves the mechanical properties, with optimal value in 170A. The ultimate tensile strength (UTS) increases by around 3 % from 605 ± 9 to 623 ± 8 MPa at 190A. The yield strengths (YS) are 370 ± 6, 384 ± 5, 371 ± 8, corresponding to 3.8 % increase at 170A then decrease 3.6 % at 190A. The microhardness increases 3.7 % with higher current, from 212.00 HV 0.5 at 150A to 293.33 HV 0.5 at 190A. The Elongation are 42.07 %, 41.8 %, and 41.3 %, slightly reduce for 150A, 170A, 190A respectively. The Microstructure analysis revealed δ-ferrite and γ-austenite dendrites, with lathy and skeletal morphology variations. [ABSTRACT FROM AUTHOR]

At present few studies have considered the mechanical properties of welded ultra-high strength (UHSS) steel after fire. In this paper, two kinds of ultra-high-strength steels Q890 and Q960 are selected as research object, and the GMAW welding method is used to connect them. An experimental study is conducted to reveal the mechanical properties of welded UHSS specimens after exposure to different high temperatures. The butt-welded UHSS and the corresponding base metal specimens are firstly heated from 200 °C to 1000 °C. After natural cooling to room temperature, the specimens are then subjected to a tensile test, and the stress-strain curves and different fracture modes are obtained. The results shown that temperature, HAZ and softening effect have an impact on the fracture mode and mechanical properties of butt-welded UHSS. Secondly, the variation law of elastic modulus of butt-welded UHSS with increasing temperature is similar to that of UHSS base metal. However, as the temperature increases, the corresponding weakening rates of yield strength and ultimate strength are significantly lower than those of the base material. Finally, based on the experimental results, prediction equations for the reduction factors of mechanical properties indicators of UHSS (base metal and welded) and HSS after fire exposure are proposed, and a comparative analysis is conducted with the existing methods. The results shown that the predictive equations proposed in this paper can more accurately calculate the mechanical properties reduction factors of UHSS (base metal and welded) and HSS after fire. • Domestic ultra-high-strength steel Q890 and Q960 are used and investigated. • The distribution of heat affected zone and different failure modes of butt-welded UHSS are studied. • Prediction equations for the reduction coefficient of residual mechanical performance of butt-welded UHSS are proposed. [ABSTRACT FROM AUTHOR]

High manganese steels have been nominated as desirable materials used for various cryogenic applications due to their excellent cryogenic toughness caused by twinning. High manganese steel welded joints were obtained through gas metal arc welding, and the microstructural differences at three subzones of heat-affected zone (HAZ) were utilized. The aim was to investigate the effect of grain size and Mn/C/Cu segregation on the cryogenic toughness mechanism of high manganese steel welded joints. The results indicate that the average impact absorbed energies at −196 °C for 1.0, 3.0, and 5.0 mm from the fusion line (denoted by FL + 1, FL + 3, and FL + 5) is 118.6 J, 102.4 J, and 117.2 J, respectively. Compared with base metal, the embrittlement occurred in HAZ. Large grains improve toughness, while small grain boundaries, segregation, and precipitation in HAZ deteriorate toughness. Larger grain size facilitates the primary twins with thinner inter-twin spacing and twin thickness, and the high density of these primary twins inhibits the activation of secondary twins. This, in turn, enhances cryogenic impact toughness. Although the stacking fault energy (SFE) throughout the welding joint lays within the range for the twinning-induced plasticity effect, the enrichment of Mn/C/Cu slightly increases the local SFE and critical resolved shear stress for twining within the segregation zone. This phenomenon makes the activation of primary twins more challenging. Furthermore, the C segregation at grain boundaries leads to the precipitation of fine Cr 23 C 6 carbides. These carbides serve as crack initiation points during impact tests, contributing to degradation in cryogenic impact toughness. [Display omitted] • Although there is embrittlement in HAZ, three subzones exhibit excellent cryogenic impact toughness. • The cryogenic toughness is attributed to the twinning mechanism controlled by the stacking fault energy. • Large grain size facilitates the primary twins with thinner inter-twin spacing and twin thickness. • The segregation of Mn/C/Cu increases the critical resolved shear stress for twining. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is an advanced additive manufacturing (AM) technology that offers low cost and high deposition rates, making it suitable for building large metal parts for structural engineering applications. However, various welding procedures result in differing heat inputs and repetitive heating treatments throughout the deposition process, which can affect the microstructural and mechanical characteristics of the parts. In the current study, cylindrical parts made of 304L austenitic stainless steel (ASS) were manufactured using the WAAM technique, employing both gas metal arc welding (GMAW) and cold metal transfer (CMT) processes. This study explores the correlation between WAAM techniques and their effects on the bead geometry, microstructure and mechanical properties. The microstructure of the cylinders consisted of vertically growing austenite dendrites with residual ferrite (δ) within the austenite (γ) matrix. Compared to the bottom region (region ①), the top region (region ②) contained more residual ferrite. Although the microstructural characteristics from region ① to region ② are similar, they exhibit different ferrite morphologies. The rapid cooling rate in the CMT-AM process resulted in finer structures and a greater presence of ferrite phases in both regions compared to the GMAW-AM method. Cylinders produced by the CMT process displayed nearly uniform properties across both regions and demonstrated superior tensile properties, hardness, and impact toughness relative to those made using the GMAW technique. The WAAM 304L ASS cylinders also showed enhanced performance compared to stainless steel manufactured using traditional industrial forging standards, indicating that WAAM-processed 304L ASS cylinders are suitable for industrial applications. [Display omitted] • Controlling heterogeneous microstructures in WAAM-processed 304L stainless steel is challenging. • GMAW vs. CMT impacts on 304L ASS microstructure analyzed. • The upward growth of coarse austenite/ferrite morphologies controlled by wire retraction mechanism. • CMT produced finer dendrites and more ferrite morphologies. • WAAM 304L ASS components outperformed than the wrought 304L ASS and forged 304L ASS. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) route is a promising approach for fabricating complex and lightweight metallic structures that have applications in various sectors such as automotive, aerospace, and biomedical industries. Laser, electron beam, and electric arc are the common power sources available for AM. Out of different metal AM techniques, wire-feed additive manufacturing has been considered as a promising alternative for fabricating metallic parts for various applications. As it provides a high deposition rate, material utilization, density, and low cost with a low risk of contamination and porosity compared to powder-based raw material. Gas metal arc welding-based additive manufacturing (GMAW-AM) is a specific approach based on wire-feed AM. This technology uses a low-cost equipment which is suitable for fabricating components with large geometries and moderate structural complexity. These advantages attract the researchers and production industries for further developments in GMAW-AM to enhance its deposition performance, process capability, and applicability in various fields. The quality of metal deposited in GMAW-AM is generally represented by the surface form, dimensional quality, mechanical properties, relative density, hardness, etc. The present paper encompasses the research developments that occurred in the field of GMAW-AM in recent years. This review begins with the GMAW-AM procedure, performance capability, identification of factors affecting the deposition performance, and strategies adopted to overcome these issues. Several aspects such as mathematical modelling, optimization, key process parameters, and their combinations for a wide range of wire electrode material and percentage contributions are also reviewed and depicted in detail. Also, a comprehensive conclusion of this review, along with future perspectives, is explored subsequently. The current review work will help future researchers to select different wire materials and GMAW-AM parameters to achieve better performances. Lastly, several future research directions are suggested, specifically the need of a framework for GMAW-AM processes for fabricating quality products with minimum distortion. [ABSTRACT FROM AUTHOR]

Fracture resistance of pipeline welds from a range of strength grades and welding techniques was measured in air and 21 MPa hydrogen gas, including electric resistance weld of X52, friction stir weld of X100 and gas metal arc welds (GMAW) of X52, X65 and X100. Welds exhibited a decrease in fracture resistance in hydrogen compared to complementary tests in air. A general trend was observed that fracture resistance in 21 MPa hydrogen gas decreased with increasing yield strength. To accommodate material constraints, two different fracture coupon geometries were used in this study, which were shown to yield similar fracture resistance values in air and 21 MPa hydrogen gas; values using different coupons resulted in less than 15% difference. In addition, fracture coupons were removed from controlled locations in select welds to examine the potential influence of orientation and residual stress. The two orientations examined in the X100 GMAW exhibited negligible differences in fracture resistance in air and, similarly, negligible differences in hydrogen. Residual stress exhibited a modest influence on fracture resistance; however, a consistent trend was not observed between tests in air and hydrogen, suggesting further studies are necessary to better understand the influence of residual stress. A comparison of welds and base metals tested in hydrogen gas showed similar susceptibility to hydrogen-assisted fracture. The overall dominant factor in determining the susceptibility to fracture resistance in hydrogen is the yield strength. • Fracture resistance of pipeline welds in hydrogen decrease with increasing strength. • In H 2 , welds and base metals of similar strength exhibit similar fracture behavior. • Two coupon geometries were used which yielded similar fracture behavior. • Strength exhibited more dominant factor in fracture than welding technique. [ABSTRACT FROM AUTHOR]

• The identification of the working status of the welder. • Promoting the intelligentization of welding work monitoring. • An improved algorithm based on SSD(single shot multibox detector). • Replacing the backbone of SSD with MobileNet, and adding a feature fusion module. As enhance of safety requirement in the smart cities, biometrics recognition, as an approach for society safety, has been greatly researched and developed. The identification of working status of welders will help judge whether they are wearing personal protective equipment correctly. We proposed an improved algorithm based on SSD (Single Shot Multibox Detector) that can identify three mainstream manual welding methods including SMAW (shielded metal arc welding), GMAW (gas metal arc welding) and TIG (tungsten inert gas), which has never been researched before and can promote the intelligentization of welding monitoring to construct smart cities. The improvement includes two parts. Firstly, the backbone of SSD is replaced with MobileNetV3. Then, a feature fusion module is added to enhance the information of low-level feature maps to improve detection accuracy. The experimental results of our welding behavior detector show that, the mAP is 87.45%, detection speed is 25FPS, and parameter memory is 87.5 MB, which has a relatively excellent performance considering speed, accuracy and memory. [ABSTRACT FROM AUTHOR]

A novel Fe–Cr–Ni–Mo weld metal containing different V content was designed and fabricated by gas metal arc welding and post-weld heat treatment. The excellent mechanical properties with a combination of high strength and good toughness were obtained by synergistic effect of nanoscale carbides, high-density dislocations and small subgrains. The discrete nanoscale carbides were characterised by transmission electron microscopy and atom probe tomography. Moreover, it was firstly found that the precipitation sites of nanoscale carbides were mainly located at inter-dendritic regions instead of dendritic core regions owing to the heterogeneous distribution of alloying elements. Image, graphical abstract [ABSTRACT FROM AUTHOR]

[Display omitted] • Welding the as-rolled CoCrFeMnNi high entropy alloy using Monel 400 filler wire via gas metal arc technique was conducted. • Welded joints were successfully obtained with full penetration and free of defects. • The weld thermal cycle changes both the microstructure features and texture distribution components across the welded joint. • The observed softening behavior within the heat affected zone is attributed to the release of pre-stored strain energy, coupled with solid-state transformations encompassing recovery, recrystallization, and grain growth. • Tensile testing, combined with DIC, reveals that fractures occur near the weld toe because of the softening effect, which activates stress concentrations. • The potential of utilizing CoCrFeMnNi joints as viable engineering structures is demonstrated. Weldability plays a crucial role in the journey of high entropy alloys towards their engineering applications. In this study, gas metal arc welding was performed to join an as-rolled CoCrFeMnNi high entropy alloy using Monel 400 as the filler wire. The present research findings demonstrate a favorable metallurgical chemical reaction between the Monel 400 filler and the CoCrFeMnNi high entropy alloy, resulting in compositional mixing within the fusion zone that promotes a solid-solution strengthening effect, counteracting the typical low hardness associated to the fusion zone of these alloys. The weld thermal cycle induced multiple microstructure changes across the joint, including variations in the grain size, existing phases and local texture. The grain size was seen to increase from the base material toward the fusion zone. An FCC matrix and finely sparse Cr-Mn-based oxides existed in both base material and heat affected zone, while in the fusion zone new FCC phases and carbides were formed upon the mixing of the Monel 400 filler. The role of the filler material on the fusion zone microstructure evolution was rationalized using thermodynamic calculations. Texture shifted from a γ-fiber (in the base material) to a strong cubic texture in the fusion zone. Digital image correlation during tensile testing to fracture coupled with microhardness mapping revealed that, stemming from the process-induced microstructure changes, the micro and macromechanical response differed significantly from the original base material. This study successfully established a correlation between the impact of the process on the developed microstructural features and the resultant mechanical behavior, effectively assessing the processing-microstructure-properties relationships towards an improved understanding of the physical metallurgy associated to these advanced engineering alloys. In conclusion, this work provides an important theoretical framework and practical guidance for optimizing the engineering applications of high entropy alloys. [ABSTRACT FROM AUTHOR]

In this study, gas metal arc welding (GMAW or MIG) process was investigated for similar and dissimilar joints of SA553 and SA537 steel plates in different thicknesses with E NiCrMo-3 filler metal and 0–3 panel joint design that joined pressure vessels body to manholes. In order to examine the metallurgical behavior of the weld, optical and scanning electron microscopies were used. The effect of cooling rate ( ∂ T ∂ t ) on microstructure, strength and impact energy (cryogenic fracture toughness) were examined. By doubling the thickness (6–12 mm), the heat transfer rate or cooling rate (∂T/∂t) increased 4 times. Therefore, the strength and impact energy for the similar welding joint SA553 increased by about 8 % and for the similar welding joint SA537 by about 5 %. For dissimilar weld joints with different thicknesses, strength and impact energy are caused by the type of base metals and the different cooling rates of each base metal. Due to the high elongation of the E NiCrMo-3 electrode (30 %), there was continuous plastic deformation during bending tests. Also, by carrying out radiographic tests, the absence of cracks in welding structures was confirmed. • For LNG and LPG storage and transportation tanks with high-pressure and low-temperature conditions, a joint with different thicknesses was welded. • The strength and cryogenic fracture toughness for the SA 553 weld joint increased by about 8 % and for the SA 537 weld joint increased by about 5 %. • A transition layer was formed between the HAZ and the weld pool, whose microstructure was completely austenitic. [ABSTRACT FROM AUTHOR]

Duplex Stainless Steels (DSSs) have excellent mechanical properties and corrosion resistance thanks to the biphasic ferritic-austenitic microstructure. This microstructure feature is highly influenced by the welding heat cycles. In this research paper, the effect of gas tungsten arc welding (GTAW) and submerged-arc welding (SAW) on the microstructure, mechanical and corrosion properties of SAF 2507 duplex stainless steel (DSS) were investigated. The base metal had the austenite content of 45 %, while the weld metals show variation of austenite contents in different regions. The middle regions of the both welds (GTAW ∼ 60.5 %, SAW ∼ 49.3 %) showed higher austenite contents than that of the root (GTAW ∼ 25.6 %, SAW ∼ 40.9 %) and top (GTAW ∼ 44.2 %, SAW ∼ 34.2 %) regions. Subsequent heat cycles promoted the precipitation of austenite from the primary ferrite, resulting in the higher contents of austenite in the middle welds. The nanoindentation tests revealed the individual properties of the typical phases, i.e., γ-Fe ∼ 5.4 GPa and α-Fe ∼ 4.7 GPa in both weld metals. The average tensile strength of GTAW and SAW welded joints are 997 MPa and 1109 MPa, respectively. The corrosion behavior of the weld metal was also evaluated through potentiodynamic polarization curves. The as-welded joints exhibit slight decrease in corrosion resistance, as compared to the base metal. These two weld metals showed slightly difference in mechanical and corrosion resistance properties. SAW method is most recommended when large thickness or high efficiency welding is required. • Structure, mechanical properties and corrosion resistance of 2507 DSS were investigated. • The content of austenite phase was highly influenced by the welding heat cycles. • SAW was most recommended when large thickness or high efficiency welding is required. [ABSTRACT FROM AUTHOR]

In the gas metal arc welding (GMAW) process, metal transfer dynamics, influenced by wire material properties such as electrical conductivity and surface tension, serve as key sources of mass and heat for metal deposition on substrates. To elucidate the role of these material properties on metal transfer dynamics from a driving force perspective, this study examined molten droplet elongation across five distinct wires: Al, Cu, Fe, Ni, and Ti. Additionally, a unique non-transferred arc welding setup equipped with a consumable wire anode and two tungsten cathodes was introduced, allowing for observations at minimized arc lengths and preventing current concentration in molten droplets. For Al and Cu wires, while only projected-spray transfer was observed under sufficient arc length conditions, a shift to minimized arc length resulted in significant droplet elongation and a transition to streaming-spray transfer. This contrast emphasized the impact of high electrical conductivity in reducing the internal gradient of electromagnetic pressure and inhibiting the occurrence of streaming-spray transfer. Further substantiating this mechanism, Fe, Ni, and Ti wires revealed that higher electrical conductivity corresponded to an increased transition current to streaming-spray transfer. Additionally, surface tension played a crucial role in the formation of molten droplets and ensured transfer stability, with its influence varying at different current levels. These insights contribute to our comprehensive understanding of arc plasma and molten metal interactions. Our study proposes material-specific strategies to optimize metal transfer dynamics, leading to enhanced control over weld bead formation and overall mechanical properties of welded joints in the GMAW. [Display omitted] • Introduction of a novel non-transferred arc welding system. • Reduction in molten droplet elongation associated with higher wire electrical conductivity. • Current concentration in molten droplets as a mechanism inhibiting molten droplet elongation. • Formation of larger droplets in the low current region observed with wires possessing higher surface tension. • Radial instability of elongated droplets in the high current region observed with a wire possessing lower surface tension. [ABSTRACT FROM AUTHOR]

Robotic welding has garnered significant attention in the maritime industry for its potential to enhance marine structure quality and optimize production processes. This systematic literature review aims to provide a comprehensive overview of the current state of research in robotic welding for marine applications, encompassing marine structures and production processes, following the PRISMA statement and guidelines. The review encompasses various facets, including welding techniques, processed materials, types of robotic welding, technological advancements, potential advantages, and challenges encountered when implementing robotic welding systems in the maritime sector. The results spotlight the pivotal role of gas metal arc welding (GMAW) in propelling robotic welding technology forward, while wire arc additive manufacturing (WAAM) has experienced a notable surge in popularity, signifying its potential to catalyze significant changes in maritime manufacturing processes. Notably, the predominant use of robotic welding centers on carbon steel materials. However, ongoing advancements indicate a growing diversification, with the incorporation of advanced materials like high-strength alloys on the horizon. Additionally, the utilization of 6-axis robot welding in conjunction with fully autonomous systems has emerged as a versatile and potent instrument that has revolutionized welding methodologies across various maritime research domains. Robotic welding provides a number of advantages, such as increased productivity, higher quality, adherence to industry standards, adaptation to confined and dangerous locations, and facilitation of innovative construction techniques. Nevertheless, adoption of this cutting-edge technology is not without challenges. By synthesizing the results from several investigations, this research study offers useful insights into the current knowledge gaps, emerging trends, and future prospects for the growth of robotic welding in maritime applications. • This review explores welding techniques, materials, advancements, and challenges. • Robotic welding improves productivity, quality, safety, and innovative construction. • WAAM emerges as a transformative and popular technique for maritime manufacturing. • Increasing use of advanced materials like high-strength alloys is on the horizon. • Valuable insights on trends and prospects in robotic welding for maritime applications. [ABSTRACT FROM AUTHOR]