Dynamic behaviors of keyhole and weld pool during the digging stage in variable polarity plasma arc welding of thick aluminum alloy

Effect of weld pool thermal history on microstructure and mechanical properties of laser oscillating welded QP980 joints

This study investigates the influence of Cr2O3-bearing fluxes on the transfer behavior of O and Cr during the submerged arc welding process. A series of fluxes with varying Cr2O3 content are prepared and applied in submerged arc welding. A cross-zone model is developed to separately evaluate the transfer of O and Cr in both droplet and weld pool zones. The results reveal significant O enrichment in the droplet zone due to the decomposition of Cr2O3 under arc heating, followed by deoxidation in the weld pool. Cr transfer is found to be inhibited by the high oxygen potential in the droplets and further affected by evaporation loss. A comparison of predicted ΔCr values shows that the gas–slag–metal equilibrium model overestimates Cr transfer level, while the cross-zone model provides predictions more consistent with experimental results. This study highlights the critical role of Cr2O3 in regulating transfer behaviors O and Cr and provides valuable insights for flux design aimed at achieving precise compositional control and improved weld quality in welding applications.

Abstract This article presents an analysis of laser welding simulation results based on the Design of Experiments (DOE) methodology. Simulations were carried out in ANSYS 18.2 software using a conical Gaussian heat source model. A full factorial 2 3 design was applied to evaluate the effects of laser power, the upper base radius, and the lower base radius of a conical heat source model, as well as their interactions, on weld pool width and volume of a fusion zone (weld pool volume). The results show that weld pool width is significantly influenced by all examined factors, with laser power and upper base radius having positive effects and the lower base radius having a negative effect. No interaction was found between these factors. In contrast, the weld pool volume is mainly affected by laser power, the lower base radius, and the interaction of both radii. Regression models achieved high accuracy (high R 2 , no Lack of Fit) and proved suitable for predicting the weld characteristics under investigation. The proposed DOE-based approach thus provides an efficient framework for optimizing welding parameters in numerical simulations.

Recognition of weld pool penetration state: a stereo matching method enhanced with weld pool details

This paper is the first of a three-part series comprehensively covering the field of high-speed videography in welding. This first part provides the fundamental concepts and resulting quantitative guidelines provided for minimum frame rates for several welding phenomena for maximum possible image resolution and the ability to capture thermal radiation from the welding process. Welding phenomena discussed include metal transfer, arc, and weld pool evolution with examples for gas metal arc welding (GMAW) and shielded metal arc welding (SMAW). The maximum possible image resolution for a given system is established based on the amount of time recorded, the buffer memory, the sensor resolution, the bit depth of the sensor, and the frame rate used. The application of Planck’s radiation law indicates that emission at low temperatures can be undetectable. Quantitative guidelines are also provided for filter type and critical wavelengths associated with light emitted by plasmas of different welding processes and thermal emission from the hot metal. Digital sensors, lenses, optical filters, and digital formats for processing and distribution are treated in detail. The fundamentals reviewed in this paper, together with the practical implementations for front and back lighting (Part 2) and natural radiation lighting (Part 3), will provide welding researchers with a previously inexistent compilation of criteria to select proper equipment, accessories and parameters for high-speed imaging of a vast variety of phenomena in welding, laser welding, and associated processes, such as additive manufacturing or cutting.

This talk presents our recent understanding about the mechanistic aspect behind the enhanced passivation behavior of a Ni-free austenitic stainless steel. Mn and N were added as austenite stabilizers and the steel was fabricated via laser powder bed fusion process. X-ray diffraction confirmed the austenitic phase, while scanning electron microscopy revealed equiaxed and columnar sub-cells along with weld pools, features typical of an additively manufactured alloy. Despite the significant Mn content, the fabricated steel showed an extremely high breakdown potential of ~ +1.18 VSCE in 0.6 M NaCl, investigated using cyclic potentiodynamic polarization. Potentiostatic tests showed no significant current spikes, indicating stable passivity. Mott-Schottky analysis of the passive film suggested a mixed semiconducting behavior of the film. Compositional analysis of the passive film was conducted using three different techniques: x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and transmission electron microscopy fitted with energy dispersive spectroscopy. All the spectroscopic studies revealed a passive film composition distinct from that of conventional stainless steel. This mechanistic understanding provides insights into tailoring the composition and processing of Ni-free stainless steel for enhanced corrosion resistance.

Inconel 625 is widely employed in high-temperature and corrosive environments, where the integrity of welded joints critically influences component performance. This study systematically investigates how laser beam welding (LBW) heat input governs cooling behaviour, microstructure evolution, elemental segregation, and the mechanical performance of Inconel 625 weld joints aiming to become sustainable joints. A single-spot monochromatic non-contact type infrared pyrometer is used to monitor the thermal cycles of the molten weld pool and the cooling rate and melt pool lifetime were determined based on the thermal cycle data. The impact of cooling rate and melt pool lifetime on weld geometry, microstructure, micro-segregation, and mechanical properties were thoroughly investigated. The findings revealed that the fibre laser welding produced sound, defect-free joints across all experimental heat-input conditions and the weld quality was fairly dictated by cooling rate during solidification. Reducing heat input (by using faster laser scan speeds) increased the cooling rate (1.45 × 103 to 3.65 × 103 °C/s), resulting in a shortened melt-pool lifetime and altered weld bead geometry from hourglass to truncated-cone profiles. Eventually, the fusion-zone microstructure transitioned from coarse cellular/columnar dendrites at high heat inputs to refined dendrites at low heat inputs. The EDS analysis revealed pronounced Nb and Mo segregation in slowly cooled welds and Laves phase formation due to insufficient time for solute redistribution and γ-Ni matrixes were consistent noted with XRD-observed peaks. The presence of the brittle Laves phase adversely affects the microhardness and tensile strength of the weld joints. Mechanical testing confirmed that decreasing heat input (in faster laser scan speeds) enhanced micro-hardness and tensile strength due to grain refinement and solute entrapment in the γ matrix. The highest joint strength (989.3 ± 10.4 MPa) and elongation (40.3 ± 1.8%) approached those of the work material, and these findings establish processing parameter–structure–property relationships for the LBW of Inconel 625. The co-relation in the present manuscript can be used in the future for process monitoring and for controlling the mechanical properties of laser welding and may provide a practical guidance for optimizing weld quality in advanced industrial applications.

This research investigates the impact of shielded metal arc welding (SMAW) electrode coating flux on microhardness, microstructure, and element transfer. A mixture design approach was employed to formulate the flux compositions, and multi-pass bead-on-plate experiments were conducted. Regression analysis was used to evaluate the relationship between microhardness and weld bead chemistry. The results indicated that the presence of CaO, Al 2 O 3 , and SiO 2 positively influences the transfer of nickel from the electrode to the weld pool. Increased levels of Na 3 AlF 6 , SiO 2 , and CaO positively affected chromium transfer, while Al 2 O 3 led to a decrease in chromium transfer. Manganese transfer was enhanced by CaO and Na 3 AlF 6 , but reduced with higher concentrations of Al 2 O 3 and SiO 2 . Furthermore, an increase in SiO 2 raised the oxygen potential, contributing to a loss of manganese in the Weld. The results indicate that increasing Al 2 O 3 positively affects iron transfer, while higher concentrations of Na 3 AlF 6 , SiO 2 , Al 2 O 3 , and CaO improve niobium transfer. Microhardness increases with higher levels of CaO, Na 3 AlF 6 , and SiO 2 , although Al 2 O 3 has a reducing effect. The welds were further analyzed through microstructural analysis. In addition, artificial neural network (ANN) models were developed, demonstrating improved prediction accuracy compared to traditional approaches.

This study investigates the thermal field of S355J2+N steel plates for shipbuilding applications welded with automatic welding equipment. Real-time thermal profiles were captured and validated using infrared thermography against SolidWorks simulations. Experimental data revealed maximum weld pool temperatures of 528 °C and sharp thermal gradients in the heat-affected zone (HAZ). The numerical model, which predicts a peak temperature of 670°C, closely matched the experimental results. An empirical relationship between welding parameters and maximum welding temperature was derived, allowing optimization of heat input and welding speed to minimize thermal distortions and residual stresses. This integrated approach improves process control and weld quality in shipbuilding.

Vibration-assisted welding has emerged as a high-quality weld production technique, with recent studies focusing on medium and high-frequency applications to enhance mechanical properties. This research aims to investigate and optimize process parameters using low-frequency vibration-assisted welding. The Taguchi method was employed to identify optimal conditions for improved weld quality. Shielded Metal Arc Welding (SMAW) was used in conjunction with a low-frequency (100 Hz) vibratory setup to impart controlled vibration to the workpiece during welding. The effects of welding current, vibration time, and frequency were optimized using Taguchi methodology and response surface technique based on an L27 orthogonal array design. The results indicate that the most important factor affecting the required hardness, tensile strength, and impact strength is vibration frequency. Vibration-assisted welding of mild steel at optimized parameters 120 A current, 100 Hz frequency, and 60 s vibration time resulted in a maximum hardness of 97.16 RHN and enhanced impact strength. Low heat input, 100 Hz vibration frequency, and 100 s vibration time yielded optimal tensile strength. SEM analysis revealed a refined microstructure in the weld zone, attributed to weld pool excitation, which promotes finer grain formation and improved mechanical properties.

Abstract Commercially pure grade 2 titanium (Cp-Ti) is important for marine and naval applications due to its excellent corrosion resistance. Additive manufacturing, especially Wire-Arc Direct Energy Deposition (WDED), enables the production of complex, large-scale Cp-Ti components but significantly alters the microstructure and properties due to thermal cycling. However, the corrosion behavior of WDED Cp-Ti in chloride-rich environments, relative to its complex microstructure, is poorly understood. This study investigates the onset and progression of corrosion in WDED Cp-Ti in HCl environments (1N-6N), revealing selective grain corrosion with evolving pitting morphology: globular at 1.25N-1.5N, pyramidal at 2N, and honeycomb-like at 6N. A novel corrosion mapping technique, combined with comprehensive electron backscatter diffraction (EBSD) analysis, reveals corrosion anisotropy within the microstructure. The grains oriented along the basal plane {0001} show superior corrosion resistance due to high in-plane atomic packing density, while prismatic planes {10 $$\bar{1}$$ 1 ¯ 0} are more susceptible to corrosion. These findings demonstrate that optimizing crystal orientation with predominantly basal planes in bulk WDED Cp-Ti can significantly enhance its corrosion resistance. This can be achieved through advanced grain orientation techniques, such as in situ ultrasonic excitation of the melt weld pool and equal channel angular pressing of WDED parts. Graphical Abstract

Abstract A novel plasma arc and powder-based Directed Energy Deposition process (DED-Arc-P) demonstrates significant potential for manufacturing high-quality metallic structures. While the process has been validated for steel and titanium alloys, its applicability to aluminum, one of the key industrial metals, remains unexplored. This study is the first to investigate AlSi10Mg processed by DED-Arc-P, focusing on the effect of welding speed and heat input on geometry, process efficiency, porosity, and microstructure to qualify the process for AlSi10Mg. The goal was to establish correlations between process parameters and material properties, and to contribute to the further development of DED-Arc-P. Results demonstrate that increased welding speeds enhance the consistency of layer height and width by minimizing heat input and accumulation. All structures exhibited higher geometric deviations in the bottom region, followed by a stable region, with the stable region achieved earlier at higher speeds due to reduced heat input. The structure produced with the highest speed showed slightly increased porosity (~ 2.7%) compared to the others (~ 2.4%). This was caused by the differences in cooling rates. Pores are primarily situated in the lower regions of all structures, attributed to effective heat dissipation by the substrate plate. The dendrite arm spacing, indicative of microstructure fineness, decreased with reduced welding speeds and higher layers as a result of increased heat accumulation. Additionally, the dendrite growth angle in relation to the build-up direction decreased with higher speeds, attributed to variations in weld pool geometry. SEM and EDS analyses revealed that higher welding speeds refine both the dendritic α-Al structure and eutectic Si particles. Fe-rich intermetallic phases, likely β-Al₅FeSi, were identified in the interdendritic regions.

Dynamic behaviour of the weld pool and joint quality during active laser welding of stainless-steel thick plates

This paper provides a new perspective on seam tracking in the welding process that has no spatial lag and does not require additional auxiliary light sources. The method is helpful for weld tracking under complex working conditions. The proposed seam tracking method is RST-REI (robotic seam tracking by REI), which is based on weld pool reversed electrode images (REIs) in the GTAW process. By using the passive weld pool image of the welding process and the relationship of REI and the welding torch pose, RST-REI achieved high-precision weld seam tracking and correction. RST-REI consists of two parts: first, a weld tracking model based on REI, which can calculate the error between the welding torch and the position to be welded through the tungsten electrode, REI, and passive image information and correct the robot pose in the welding process; second, an efficient and robust image processing algorithm, which uses the segment anything model to extract the electrode and REI foreground image in the weld pool image in real time. With the help of quadratic curve fitting, it could accurately extract the required parameters for calculating the welding torch pose in the RST-REI model. Furthermore, the experimental results of straight-line, right-angle, and S-shaped weld seams showed significant performance with the tracking error within 30 pixels, which was about 0.5 mm in our experiments. The tracking results met the weld tracking requirements of the actual welding process.

TThe microstructure and mechanical properties of AlSi10Mg aluminum alloy sheets produced by additive manufacturing method were revealed. It was clearly observed that the microstructure consisted of weld pools separated by boundaries. Furthermore, a small number of distributed pores with diameters ranging from 35 µm to 5 µm were detected in the microstructure. A few small-sized pores are a sign of good production. Vickers microhardness of the produced AlSi10Mg alloy was measured to be average 126.625 HV. Additionally, its tensile strength and three-point bending strength value were found to be 433 MPa and 548 MPa, respectively. The tensile fracture surface had many small and deep dimples while three-point bending fracture surface also possessed dimples, however, bigger and shallower compared with that of tensile fracture. Therefore, the tensile and three-point bending tests showed a reasonable ductile fracture behavior.

Introduction. Increasing the productivity of single-wire surfacing through raising the wire feed rate causes defects — undercuts and poor fusion between layers, which reduces the quality of the deposited coating and increases the reject rate. To solve this problem, multiwire surfacing techniques are being developed in a shielded gas environment which increase productivity without compromising quality. The literature shows that the relative position of electrodes in multiwire systems affects significantly the thermal and electrophysical characteristics of the arc, and therefore, the geometry of the reinforcement and the shape of the fusion penetration. However, the available studies are fragmentary: there is insufficient data on the morphology of the fusion zone, and the relationship of its parameters and specific electrode arrangement schemes under twin-arc surfacing in a shielded environment, which leaves a scientific gap. The objective of this research is to evaluate the change in the geometric parameters of the reinforcement of the deposited layer and the morphology of the fusion zone with different relative positions of the electrodes under twin-arc surfacing in a shielded gas environment.Materials and Methods. The experiment was conducted on a 6-axis Fanuc 120iD robot with an EWM Titan XQ500 power source and an experimental surfacing head consisting of two welding torches. The layers were deposited on steel substrates of grade St3 using the GMAW Pulse method with Sv 08G2S wire with a diameter of 1.2 mm in an Ar/CO₂ environment (98%/2%) under a fixed surfacing mode (WFS = 6.5 m/min for each torch, TS = 4 mm/s, MW = 150°C). The following parameters were adopted as the studied factors: distances between electrodes (z = 15, 18, 21 mm), their angle of inclination (α = 5°, 10°). On the cross-sections of the deposited layers prepared by grinding and etching, the geometric parameters of reinforcement (height h, width S, wetting angle γ) and fusion penetration (depths a, a₁, width b) were measured. Quantitative analysis of the weld geometry was performed using Digimizer software to assess the effect of the relative position of the electrodes on the formation of the layer.Results. It has been found that the distance between the electrodes (z) affects significantly the reinforcement geometry: a growth of z causes an increase in the layer width (S) and the wetting angle (γ), but a decrease in its height (h). The axial fusion depth (a) demonstrated a nonlinear dependence on z, reaching a maximum (~2.2 mm) at z = 18 mm. The inclination angle (α) had a minor effect (<5%)on the reinforcement parameters, but affected significantly the shape of the main fusion zone (a₁): an increase in α decreased a₁ and made the penetration more gently sloping. At z = 21 mm, the impact of α on the penetration disappeared. The relationships between the relative positions of the electrodes under twin-arc surfacing, the geometric parameters of the reinforcement, and the depth of the fusion zone were specified.Discussion. The explanation of the established dependences is based on the change in the thermal and electrophysical properties of the electric arc depending on the mutual arrangement of the electrodes. The axial depth of fusion penetration depends not only on the distance between the electrodes, but also on the volume of the weld pool. With an excessive volume of the weld pool for a specific surfacing mode, a damping effect of heat flows from the electric arc to the base metal occurs — the volume of the weld pool absorbs part of the heat, which causes a decrease in the depth of penetration. The change in the arc pressure vector with an increase in the angle between the electrodes explains the decrease in the depth of the main fusion zone.Conclusion. The regularities of the effect of the mutual arrangement of electrodes on the geometry of the deposited layer and the shape of the fusion zone under twin-arc surfacing in a shielded gas have been experimentally established. It is shown that an increase in the distance between the electrodes results in an increase in the width of the bead, a decrease in its height, and an increase in the wetting angle. It has been noted that the penetration depth depends on the volume of the weld pool. It is determined that the angle of inclination of the electrodes in the studied modes has an insignificant effect — less than 5% — on the geometry of the deposited metal, although hypothetically, it can be enhanced at smaller interelectrode distances. The data obtained extract clear trends and form the basis for further in-depth study of the thermal and electrophysical aspects of the process of twin-arc surfacing in a shielded gas environment.

Abstract This study aimed to clarify the influence of a longitudinal external magnetic field (EMF) on arc characteristics, metal transfer behavior, and weld bead formation in metal-cored arc welding (MCAW) process. The work focused on comparing two distinct conditions: without EMF (0 mT) and with EMF applied at a magnetic flux density (MFD) of 6 mT, evaluated by high-speed video observations and numerical simulation models for a welding current of 320 A. Experimental results indicated negligible changes in droplet transfer frequency between the two conditions, but significant differences were observed in arc behavior and weld pool characteristics. The application of EMF intensified arc brightness and increased weld penetration depth from 3.7 mm (no EMF) to 4.2 mm (EMF 6 mT). Simulation results revealed that EMF induced rotational plasma flow and reduced pressure at the arc column center, which resulted in an increased plasma velocity directed toward the weld pool surface. Consequently, a depression was observed at the weld pool surface to enhance the weld bead penetration. The findings highlight the potential of EMF as a valuable tool to optimize MCAW processes, particularly when precise penetration control and improvement of weld quality are required.

Abstract This study investigates the influence of the duty cycle, with two different torch angles, on the transient development of the weld pool during pulsed current gas tungsten arc welding (PC-GTAW) in lap joints of thin aluminum sheets. A numerical model was developed to accurately evaluate the heat flux, current density, and gas shear stress generated by the arc plasma. These parameters were then used in another model to forecast the weld pool geometry with three pulsed current duty cycles: 20%, 50%, and 80%. Analyses were conducted using torch angles of 20° and 45°. Torch angles significantly affected the arc and weld pool characteristics. Variation in heat flux distribution was observed with the 20° torch yielding higher heat flux on the horizontal surface compared to the vertical, whereas the 45° torch showed slightly high heat flux on the horizontal surface, contrary to symmetry expectations. Results indicate that welding with a 20° torch produced a deeper and wider weld compared to the 45° torch. The 20° torch produced full penetration under the direct current condition, whereas a 45° torch led to partial penetration and asymmetric pool formation due to the joint geometry. Duty cycle also affected the weld pool. At a 20% duty cycle, the weld pool got sufficient time to solidify during each pulse cycle, while at 80% duty cycle, a continuous liquid pool was maintained. Increasing the duty cycle from 20% to 80% developed larger pool sizes for both torch positions. The numerical model was validated with macrostructural images obtained from real experiments giving good agreement between the two. The findings highlight complex interactions between arc plasma dynamics, duty cycle ratios, and weld pool characteristics in PC-GTAW, offering insights for optimizing welding parameters to minimize distortion in thin aluminum sheets in future studies.

Method of weld pool processing for defect recognition based on generalized heat source fusion