Narrow Heat-affected Zone Research Articles

Microstructure characterization and formability assessment of electron beam welded Nb-10Hf-1Ti (wt.%) refractory alloy sheets

Formability study on welded blanks of Nb-based refractory alloy C-103 (Nb-10Hf-1Ti (wt.%)) has tremendous potential for utilizing smaller sheets for realization of large-size divergent portions of upper-stage liquid engine nozzle of satellite launch vehicles and thrusters of attitude orbital control systems. In this work, vacuum-annealed monolithic C-103 sheets were electron beam welded successfully to obtain defect-free welds and detailed microstructural and mechanical characterizations were investigated. Columnar epitaxial grains were found in fusion zone (FZ) instead of equiaxed grains in base metal (BM). Detailed SEM and HRTEM analyses revealed spherical shape of nano-sized HfO2 precipitates with monoclinic crystal structure in the C-103 sheet. Further, microhardness across the weld cross-section indicated that the FZ had a uniform and maximum hardness of ∼195 HV0.5 due to formation of finer nano-sized HfO2 precipitates with higher number density, followed by a lowering of hardness in a narrow heat-affected zone. A marginal reduction in tensile strength of ∼6% with a considerable decrease in ductility of ∼29% was noticed for the welded sample. However, fracture occurred in the BM region, indicating good weld integrity. Furthermore, formability of the welded blanks was evaluated in terms of limiting dome height (LDH), forming limit diagram, and deep drawn cup depth. The effect of the presence of WZ on the formability of the C-103 sheet was estimated under uniaxial, plane strain, and biaxial tensile strain paths for the first time, and the results were compared with the monolithic sample. It was noted that the failure limit of the welded specimens decreased compared to that of the monolithic sample, resulting in a lower LDH of approximately 69% and 62% when deformed along plane strain and biaxial tensile strain paths, respectively. However, a marginal variation in LDH was observed for the uniaxial strain path. Also, the welded blank had more resistance to material flow into the die cavity due to the harder weld region, resulting in a reduction of deep drawn cup depth by 52% than that of the monolithic blank. The overall results concluded that the presence of the WZ significantly affected the formability of the C-103 sheet, especially in plane strain and biaxial strain paths. However, the fracture was never found to be propagating along the weld line, indicating the ability of the weld to sustain large plastic strains. This study provides insightful information on the formability of electron beam welded C-103 sheets for the successful fabrication of space components.

Tensile testing of S690QL1 HSS welded joint heterogeneous zones using small scale specimens and indentation methods

Abstract The welded joints are structures with significant heterogeneity, indicated by their fundamental segmentation into base metal (BM), heat affected zone (HAZ), and weld metal (WM). The heat affected zone, having width in millimeter scale for fusion welding processes, is further segmented into several characteristic regions, having differences in grain structure and size. The microstructural heterogeneity results in significant differences in mechanical properties of individual welded joint zones. Mechanical testing of such small material volumes is inconvenient, or even impossible, using the standard size specimens proposed in testing standards. Requirement to precisely position the specimens, even ones with subsize dimensions, and investigate mechanical properties of specific narrow HAZ regions presents certain challenge. This work investigates the X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The material tensile properties are tested, using small scale specimens and indentation methods. Small scale specimens are ASTM E8 round tensile subsize and flat sheet mini tensile specimens (MTS). The indentation methods include hardness testing and profilometry-based indentation plastometry (PIP) method, to gain additional insights into material stress–strain behavior. Finally, paper evaluates the testing methods, comparatively processes the collected experimental data, and provides guidelines for heterogeneous structures testing.

Technology development of novel autogenous double pulse tungsten insert gas welding technique to evaluate the depth of penetration, micro segregation via machine learning and desirability function approach

The present research investigates the effect of process parameters on the microstructure, micro segregation, and material properties of the Autogenous Double Pulse Tungsten Inert Gas Welding (ADP-TIG) of Inconel 625. The optimization of the process parameter was evaluated by Response surface Methodology (RSM) Box Behnken method. In this article, the effects of the weld-bead geometry, weld centre (WC), weld interface (WI), and heat affected zone (HAZ) were evaluated through macro morphology, microstructure, SEM/EDAX, XRD, and micro hardness. The outcomes indicate that by employing a combination of high and low frequency pulsing in ADP-TIG, it is possible to regulate not only the dimensions of the weld-bead and penetration depth but also the HAZ. The ADP-TIG process has a low heat input, resulting in finer grains in the microstructure, reduced secondary phases, and a narrower HAZ. SEM images of alloy 625 confirms the depiction of fine equiaxed dendrites. The ADP-TIG process reduces secondary phase formation due to a reduction in Mo and Nb alloying elements. EDAX results also show that the micro segregation in the weld centre (WC) and weld interface (WI) is very less in the dendritic core region because of the lower heat Input. The XRD result confirms the presence of NbzNi, Cr₂Nb, Ni8Nb, Fe2Mo3 and FeNi phases. The maximum microhardness values in WC and WI are 290 HV and 280 HV, respectively. The impacts of ADP-TIG welding technique specifications on factors such as weld bead geometry, WC, WI, and HAZ have been thoroughly examined across a range of process parameters. Further the process parameters of ADP-TIG were optimized using a desirability function to achieve defect-free welds, followed by experimental validation. The desirability function results were then compared with a machine learning (ML) approach. The investigation aimed to assess ML algorithms' predictive capability for weldment outcomes. From the ML modelling results, Support Vector Machine (SVM) using the Radial Basis Function (RBF) kernel was identified as the superior strategy for accurately predicting Heat input, Mo segregation, and Nb segregation. Additionally, Gaussian process regression (GPR) with an RBF kernel was recommended for predicting the Width to Depth Ratio.

Mechanical response and microstructural evolution of a composite joint fabricated by green laser dissimilar welding of VCoNi medium entropy alloy and 17-4PH stainless steel

In engineering structures, the application of advanced alloys, such as the VCoNi medium-entropy alloy (VCoNi-MEA), with remarkable tensile strength (> 1 GPa) and superior ductility necessitates the employment of dissimilar joints. This study pioneers the dissimilar joining of VCoNi-MEA and 17–4 precipitation hardening stainless steel (17–4PH STS) using state-of-the-art green laser beam welding (LBW). To evaluate and optimize the experimental parameters, two welding speeds (200 and 300 mm/s) along with post-weld heat treatment (PWHT) were incorporated. High-quality welded joints with a single-phase face-centered cubic (FCC) structure in the fusion zone (FZ), minimal precipitates (< 1.6 %), and no visible cracks were successfully created. The LBW process demonstrated effective low-heat input characteristics, evident from a considerably narrow heat-affected zone (HAZ). Control over FZ width and grain size was achieved, measuring 600 and 112 μm at low welding speed and 250 and 49 μm at high welding speed, respectively, significantly lower than previous studies. A remarkably high yield strength (YS) of ∼620 MPa and ultimate tensile strength (UTS) up to 845 MPa were observed in the as-welded conditions, improving to ∼645 and 875 MPa, respectively, after PWHT. This enhancement in mechanical properties is primarily attributed to lattice friction induced by V addition. PWHT also improved joint ductility, increasing from 3.5 % to 8.6 % (low-speed) and from 6.3 % to 9.2 % (high-speed). The reduction in crystallographic orientation achieved using a higher welding speed and PWHT emerged as a major reason for improved mechanical properties. Slip-based deformation mechanisms dominated across all conditions, featuring crystallographically aligned slip bands. Interactions between existing and additional slip bands formed a dense dislocation network crucial for enhanced elongation after PWHT. Thermodynamic parameters elucidating phase stability in the observed FZs and contributions to superior YS were calculated and comprehensively discussed.

Microstructural and mechanical properties of electron beam welded super duplex stainless steel

The electron beam welding of super duplex stainless steels is associated with challenges due to the concentrated heat input and the nitrogen loss that result in a predominantly ferritic structure after the solidification. This study presents an approach to overcome this issue by feeding nickel-based filler wire into the melt pool in welding of 2507 super duplex stainless steel. Results showed that the high-frequency beam oscillation combined with a multi-beam technique led a good mixing between the base metal and the filler wire, even at a large depth-to-width ratio. Additionally, the weld geometry was characterized by near-parallel fusion lines and a narrow heat-affected zone. The nickel addition resulted in a balanced microstructure in the weld metal with ferrite fractions of 35–55 %, despite a significant nitrogen loss, consequently leading to impact energy values of 215 ± 15 J and hardness values of 285 ± 15 HV. The findings of this investigation allow fabricators to effectively design electron beam welding processes for producing thick-walled super duplex stainless steel components.

Nanomechanical, mechanical and microstructural characterization of electron beam welded Al2219-T6 tempered aerospace grade alloy: A comprehensive study

As compared to traditional fusion welding processes, electron beam welding (EBW) is known to produce structurally robust microstructures and narrow heat-affected zone (HAZ) in metals. The process becomes more significant for the tempered alloys vulnerable to heat exposure. In the present investigation, Al 2219-T6 alloy was joined using the EBW process. The microstructural, mechanical, and nanomechanical characteristics of the resulting joint were investigated. EBW resulted in a narrow HAZ (22 μm) with a 430 mm fusion zone (FZ). A dendritic structure was observed in the FZ zone, while second-phase particles were absent indicating their dissolution during welding and interesting formation of Al2Cu mixture around the dendrites. The limited content of Cu in the base metal (BM) resulted in the formation of a solid solution in the FZ, along with the presence of fine equiaxed grains in the HAZ and equiaxed dendritic grains in the FZ zone. The X-ray diffraction analysis confirmed the absence of peaks corresponding to incoherent phases in the FZ. Compared to the BM, micro-hardness measurements revealed a 12.7 % increase in the hardness in the HAZ, while a significant decrease of approximately 19 % was observed in the FZ. The joint exhibited reduced tensile strength, ultimate strength by 42.2 %, and yield strength by 47.3 % when compared to the BM. The fracture analysis indicated a ductile failure mode with the presence of microvoids. Nano-indentation tests at various loads demonstrated a decrease in the nanohardness from the BM to the HAZ and FZ regions. Atomic force microscopy (AFM) analysis revealed significant pile-ups in the FZ, indicating the occurrence of plastic deformation during the welding process. The presented findings are valuable for the joint and structure design of Al −2219T6 alloy in particular and other Al alloys in general.

Gleeble Simulation of HAZ in S690QL Steel: Microstructural and Mechanical Properties

When investigating the heterogeneous properties of welded joints, mechanical testing of certain Heat Affected Zone (HAZ) regions, using standard approach test specimens, is very difficult or sometimes even impossible. Inability to precisely position and extract mechanical test specimens, even ones of the subsize dimensions, from the narrow HAZ regions is a limiting factor in the mechanical testing implementation. Detailed investigation of the HAZ is made possible by the use of thermo-mechanical simulations on the Gleeble welding simulator. In scope of this paper several characteristic HAZ microstructures of S690QL grade High Strength Steel (HSS) are being simulated. Multi-pass welding simulations are done on special 10x10 mm square section bar specimens in order to reproduce thermal gradients and characteristic microstructures at any location in a weld. Such simulated HAZ microstructures are of a sufficiently large volume, with homogeneous and repeatable properties, that standard specimen methods for mechanical testing can be readily implemented. Metallographic optical examinations, as well as hardness measurements were done initially. Mechanical properties are focused on determining stress-strain curves for each characteristic weld region. The paper investigates whether the mechanical properties of Gleeble simulated hard-soft combined HAZ regions are better in comparison to exclusively hard or soft HAZ regions. The obtained results can subsequently be used for the material model development.

Elucidating the effect of circular and tailing laser beam shapes on keyhole necking and porosity formation during laser beam welding of aluminum 1060 using a multiphysics computational fluid dynamics approach

In the attempt to produce lighter battery packs at a lower cost, replacing common copper parts with aluminum components has been a popular approach in recent years. With regard to joining technologies, there is a growing interest in applying laser beam welding in battery pack manufacturing due to several advantages such as single-sided and noncontact access while maintaining a narrow heat-affected zone. Motivated by the need to control and reduce weld porosity in AA1060 battery busbar welding with the ultimate goal to enhance durability and reduce electrical resistance, this paper has been developed with the aim to studying the effect of laser beam shaping on porosity formation and, hence, generate knowledge about the underlying physics of the welding process itself. First, a multiphysics computational fluid dynamics model has been developed and calibrated to experimental data; then, the model has been deployed to study the effect of both circular and tailing beam shapes on melt pool dynamics and the evolution of porosity due to the instability of the keyhole. The study elucidated the importance of the keyhole’s necking on porosity formation. Findings showed that the tail beam shapes, compared to the circular spot, have a pronounced effect on the reduction of the necking effect of the keyhole—this helps to reduce number of collapsing events of the keyhole itself, thereby leading to the reduction of porosity formation.

Utilization of multi-pass laser processing strategy for enhancing the capability of low power ns laser for machining of Ti-6Al-4V alloy

The present study aims to investigate the deep machining of Ti-6Al-4V alloy using a nanosecond (ns) laser through multi-pass and gas pressure. Experiments were conducted based on Full factorial design (FFD) by varying gas pressure and laser process parameters (LPP). Results showed that deeper grooves could be achieved through multi-pass laser scanning support with appropriate gas flow rate and laser parameters. A higher gas flow rate leads to more efficient removal of material and a faster machining rate. Further, the present findings revealed the substantial influence of laser power on the depth and width of the machined features, accounting for 41.28% and 7.11% of the variations, respectively. Moreover, power exhibited a significant impact on the taper angle (20.69%) and the heat-affected zone (HAZ) (12.04%) during the machining process. Additionally, the utilization of a multi-pass laser scan demonstrated a remarkable effect on the depth (1.89%), width (3.3%), HAZ (9.96%), and taper angle (8.78%). Furthermore, the assisted gas flow rate displayed a significant influence on the machined groove profile, that is, depth (41.97%), width (67.6%), HAZ (65.48%), and taper angle (30.15%). To achieve optimized results for high-depth machining with minimal defect, the present study recommends employing an average power of 40 W, an assisted gas flow rate of 25 L/min, and conducting four passes. These parameters develop laser machined surface with a high depth (~1499 µm) while simultaneously minimizing Taper (1.87°) and narrow HAZ (83 µm). Further, these conditions are suitable for laser cutting, trepanning, and surface texturing using a low-power laser system of Ti-6Al-4V alloy.

Numerical simulation and testing of laser-MIG hybrid-welding angle-structure sheets.

Numerical simulation and experimental investigation of laser-MIG hybrid angle-welding low-carbon 1.5-mm-thin SPCC steel sheets are presented in this work. The transient simulation analysis provides an access to the thermal-fluid phenomena prediction by employing a hybrid three-dimensional heat source model. Special attention is paid to the melt dynamic behaviors within the triangular molten pool affected by the Marangoni convection. The simulation results show that the temperature and its gradient distribution are symmetrical with respect to the laser beam, which is validated well by the experimental study. The microstructure of the welded joints was analyzed by scanning electron microscopy and transmission electron microscopy. The results show that the cross-section microstructures of welded joint are mainly composed of the weld zone, narrow heat-affected zone, and substrate. The semielliptic-like molten pool shape is consistent with that of the simulated results. The finer microstructure in the weld bead results from the rapid cooling rate of laser welding confirmed by the FEM calculation. The columnar and equiaxed dendrites are formed in the peripheral and central region of the molten pool, which is beneficial for the improvement of the microhardness.

Effect of Heat Treatment on Corrosion and Mechanical Properties of M789 Alloy Fabricated Using DED

The directed energy deposition (DED) process offers potential advantages, such as a large building space, limited dilutions, narrow heat-affected zones (HAZ) and potentially improved surface properties. Moreover, heat treatments have been reported to significantly improve the properties of the as-built sample by modifying the microstructure. In this study, the influences of various combinations of heating and cryogenic treatments on the mechanical performance and corrosion resistance of DED M789 steel have been critically investigated. The microstructure and hardness were examined to discuss the characteristics of the M789 parts in the as-printed and heat-treated states. The corrosion rate was determined from the weight loss monitoring based on the seawater immersion condition. The microstructural results revealed the distortion of martensite lattice and the formation of nano-carbide precipitates after the cryogenic treatment. Moreover, the microhardness of the cryogenically treated M789 steel was found to be significantly higher which was attributed to the precipitate strengthening and elimination of retained austenite, resulting from the increased volume fraction of carbides due to cryogenic treatment. The corrosion characteristics were also modified by the heating/cryogenic treatments, and the substrate-to-deposit ratio of the corrosion sample also substantially affected the overall corrosion rate.

Orbital friction welding of steel bars – heat generation and process modelling

Welding of rails in the field is usually associated with a large heat input, which results in a large heat-affected zone (HAZ), which in turn may impair the welded rail head and decrease its service life. An innovative orbital friction welding (OFW) process with an intermediate eccentrically oscillating disk is proposed, and a demonstrator has been constructed. This enables welding of rails, which have a non-symmetric cross-sectional area and must be stationary during welding. The process is characterized by low heat input, creating a narrow HAZ, and low welding deformations. A thermo-mechanical finite element model is developed to determine suitable process parameters to create a narrow HAZ. A phenomenological model for heat generation during friction welding is developed for pearlitic rail steel with parameters calibrated from rotary friction welding experiments on pipes. The temperature dependence of the friction coefficient in the interface is established. Pilot tests with the demonstrator OFW machine on bars with a quadratic cross section showed that preheating will be required to guarantee a fully pearlitic weld zone. This was verified by the simulations of the thermo-mechanical finite element model.

Study of the properties of high silicon aluminum alloy by laser welding

High silicon aluminum alloy is a kind of high-performance electronic packaging material, due to its excellent thermal conductivity, low thermal expansion coefficient, and low density. The heat affected zone (HAZ) of conventional welding techniques is too wide to weld the high silicon aluminum alloy, as wide HAZ will improve risk of cracking. Laser welding with narrow HAZ, high joint strength, and good morphology, has been considered as a promising method to weld high silicon aluminum alloy. Herein, the surface morphology, microstructure, and microhardness of laser welding joint between Al-50wt.%Si and Al-27wt.%Si alloys were investigated. It has been found that welding speed at 3 mm–5 mm/min can significantly reduce the hydrogen pores and cracks in laser welding joints. Also, the key paraments of laser welding to control the quality of joints are power and pulse width, while the former one is mainly controlling the joint width and the latter one is significantly changing the joint depth. Along the horizontal direction of laser welding joints, the microhardness increases firstly and then decreases, with the highest microhardness of 167 HV in the weld zone. Because the laser welding method could produce uniform microstructure of joints, the microhardness of joints is uniform along the longitudinal direction. The tensile properties of welding samples are almost the same with the properties of the Al-50wt.%Si base materials.

Application of a high-speed infrared thermographic camera to the study of HAZ softening in S960 welded joints

Hot strip rolling of low-carbon advanced high-strength (AHS) sheet steels is difficult because their products require specific chemical compositions to achieve excellent mechanical properties. The formation of a heat-affected zone (HAZ) during welding is therefore a challenge in terms of maintaining high strength values. This fact complicates the formation of the softening area when the hardness in the HAZ rapidly decreases. According to the continuous cooling transformation diagram (CCT), the chemical composition of the base metal is directly related to the fine-grained martensitic microstructure arising from very high cooling rates and microalloying up to 0.2 wt% by Nb, V, and Ti. The gas metal arc welding (GMAW) was used to perform the study, what presents a challenge for thin sheets because of very narrow HAZ formation, suscepible to HAZ softening phenomenon. The width of the HAZ was about 6 mm and determined by applying an infrared thermographic camera to measure the real-time temperature development. The significant reduction in microhardness, known as the softening phenomenon, occurred in the intercritical heat-affected zone or at the boundary between intercritical and subcritical HAZ, according to real-time diagnostics of the temperature development and the microhardness results. The amount of heat produced during welding plays an important role in this context and is directly connected to the heat input of the welding process. The softening area can be reduced and its impact on the mechanical properties can be lowered by appropriately modifying the welding conditions, e.g., optimising the heat input. The purpose of this paper is to point out the change in temperature during the welding process.

Joining different grades of low carbon steel to develop unsymmetrical rod to plate joints using rotary friction welding for automotive applications

The main objective of this investigation is to optimize the rotary friction welding (RFW) parameters for maximizing the tensile strength (TS) and weld interface hardness (WIH) of rod to plate joints of different grades of low carbon steel and analyze the effect of RFW parameters on TS and WIH of joints. AISI 1018 and AISI 1020 grades of low carbon steel are joined to develop unsymmetrical rod to plate joint using RFW for automotive applications. RFW being a solid-state welding (SSW) was employed to avoid the problems in fusion welding and development of unsymmetrical joints such as solidification cracking, wider heat affected zone (HAZ) and distortion. The RFW parameters specifically friction pressure/friction time (FRNP/FNRT), forging pressure/forging time (FRGP/FRGT) and rotational speed (rps) were optimized using response surface methodology (RSM) to maximize the strength and hardness of rod to plate joints. The three factor – five level central composite design (3 × 5 - CCD) consisting of less experiments was employed for designing experimental matrix. The tensile strength and microhardness tests were performed to evaluate mechanical performance of rod to plate joints. The numerical and graphical optimization techniques of RSM were employed to optimize the RFW parameters. The 3D response surfaces were developed which show the optimum conditions of RFW parameters. The effect of RFW parameters on TS and WIH of rod to plate joints was analyzed from 3D response surfaces. The microstructural features of optimized rod to plate joint were analyzed using optical microscopy. The fractured surfaces of rod to plate joints were analyzed using scanning electron microscopy. Results showed that rod to plate joints developed using FRNP/FRNT of 3.71 MPa/s, FRGP/FRGT of 3.71 MPa/s and RTSP of 19.99 rps exhibited higher TS and WIH of 452 MPa and 252 HV0.5 respectively. The higher TS and WIH of rod to plate joints is attributed to the evolution of finer grain structure in weld zone and narrower HAZ. The RTSP revealed greater effect on TS and WIH of rod to plate joints followed by FRGP/FRGT and FRNP/FRNT.

Remote laser spot welding of AISI 430 sheets by fiber lasers—A phenomenal effect in refining weld microstructure with nanosecond pulses

In the present work, we have compared the results of microstructural and mechanical property characterization of AISI 430 ferritic stainless steel spot welds made remotely using a repetitive nanosecond pulsed fiber laser and a CW fiber laser. Optical/electron microscopy, microhardness test, and tensile shear tests were performed for evaluation of the welds. Welds made by the pulsed nanosecond laser were found to be superior due to the presence of the very narrow heat-affected zone along with finer grains in the fusion zone. The welds were also found to withstand more load before fracture and were more ductile. Use of short duration laser pulses with lower heat input were found to be responsible for the refinement of grains in the fusion zone and improvement of mechanical properties of nanosecond laser weld specimens.

Electron beam welding of 2205 duplex stainless steel with nickel-based filler wire using multi-beam technique

The duplex stainless steels have many favorable properties attributed to their two-phase microstructure consisting of almost equal fractions of ferrite and austenite. Therefore, they are widely used in the offshore, petroleum, and chemical industries as a base material for pressure vessels and pipelines. Such components often possess large thicknesses, which can be effectively welded with electron beam. This process is characterized by rapid cooling combined with a relatively great loss of nitrogen, resulting in insufficient austenite formation. To compensate this phenomenon, the addition of nickel, in the form of wire, was performed in this study. This promoted the formation of austenite at the same cooling rate, so that approximately an equal amount of ferrite and austenite was achieved. Beam oscillation was applied to maintain good dilution even at large depth/width ratios. Furthermore, the multi-beam technique was implemented to reduce the spatter formation and provide a higher process stability. This allows the spatial, but not temporal, separation of the melting-off of the wire and the main welding process. The joints produced in this way exhibit a good weld dilution and consequently an austenite distribution with a low inhomogeneity. Additionally, a narrow heat-affected zone was produced.

Local microstructure and mechanical characteristics of HAZ and tensile behavior of laser welded QP980 joints

Microstructural evolution of the heat-affected zone (HAZ) seriously affects the mechanical properties of the welded joints. In this paper, QP980 steels were butt-welded by fiber laser. The thermocouple and Gleeble1500 system were used to achieve the thermal simulated HAZ specimens of laser welded joints, which solved the problem that it was difficult to evaluate the mechanical properties due to the narrow HAZ of the laser welding. Large amounts of granular carbides were precipitated in the block martensite of the sub-critical HAZ (SCHAZ). Carbides were not found in lath martensite, but there were dislocation tangles in the lath martensite of the SCHAZ. In addition, the number of dislocations in the ferrite of the SCHAZ was significantly reduced. The SCHAZ had the lowest strength but the highest elongation owing to the tempering. The fine-grain strengthening resulted in the highest tensile strength in the fine-grained HAZ (FGHAZ). The tensile fracture morphologies indicated a brittle fracture mechanism in coarse-grained HAZ (CGHAZ) and FGHAZ, and exhibited a ductile fracture mechanism in the inter-critical HAZ (ICHAZ) and SCHAZ. According to the overview of the joint and the local mechanical characteristics of HAZ, the numerical model of the tensile test was performed by ABAQUS. And the simulation results showed good agreement with the experimental results, which both illuminated the constraint effect of SCHAZ and made the strain concentration transferred from SCHAZ to the BM with the increase of stress.

Analysis of metal transfer and weld forming characteristics in triple-wire gas indirect arc welding

Triple-wire gas indirect arc welding (TW-GIA) has the advantages of low heat input and high deposition rate. However, the simultaneous melting of triple wires makes the metal transfer mode complicated. The unknown of the metal transfer mode restricts the development of this technology. In this paper, high-speed camera systems and electrical signal acquisition sensors were used to explore the TW-GIA metal transfer mode. The static force model and the arc conductive channel model were used to discuss the droplet force and energy conversion characteristics, respectively. Results showed that the TW-GIA metal transfer modes can be divided into the following: short-circuit transfer (SCT), main wire projected transfer + side wire globular transfer (PGT), main wire streaming transfer + side wire projected transfer (SPT), and main wire streaming transfer + side wire streaming transfer (SST). Moreover, the process parameter ranges corresponding to the four modes were summarized. Due to the stable arc and the uniform metal transfer process, SPT and SST can form desirable weld seam. The gravity and z-axis components of electromagnetic force are the main forces that promote metal transfer. The x-axis and y-axis components of the electromagnetic force deviate the metal transfer path from the arc coverage. Due to the change of arc conductive channel, the energy transferred from TW-GIA to the base metal is less than that of gas metal arc welding, showing the advantages of small welding deformation, narrow heat-affected zone, and grain refinement.

Analysis of Stress Intensity Factor on Weld Surface

Progressive welding technologies based on high energy density welding process such as electron beam welding allow joining two materials without consumable. The nature of the process is the deposition of energy to the small areas, which leads to the creation of a narrow heat-affected zone (HAZ). Therefore, a prime example of surface weld defects in the case of the beam electron welding technology are cracks in the material. The article is focused on the preparation of a computational model that comprises a precise description of welding joint shape. The accurate model description was acquired using 3D scanning. In the next step, the data are subsequently modified in MATLAB and ADINA for model simplification. The performed analysis of results shows a significant influence of the weld surface on the occurrence of stress concentrations in the weld zone.