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The paper deals in depth with characterizing bead-on-plate welds on EN-GJS-500-14 base metal, utilizing two filler metals: a pure Ni wire and a NiFe wire containing 45 wt pct Ni. The welds were conducted using the same heat input to ensure comparability in microstructure analysis. The microstructural observations were carried out using optical and scanning electron microscopies, X-ray tomography, X-ray diffraction analysis, and microhardness testing. Thermodynamic simulations using the non-equilibrium Scheil solidification model provide insights into the solidification process and the underlying metallurgical factors associated with the observed microstructural evolution. The observations revealed that the pure Ni wire deposited a softer fusion zone with graphite precipitation, while cementite precipitated in the fusion zone of NiFe alloy. The formation of martensite structures with different morphologies was the predominant microstructural evolution in the heat-affected zone of both welds. The partially melted zone of the pure Ni weld is narrower than the NiFe weld because more diffusion of Ni avoids widening the brittle structures in the partially melted zone. An unmixed zone in the form of a peninsula was exclusively observed in the fusion zone of the NiFe weld because of inadequate diffusion of Ni into the liquified materials along the fusion boundary. [ABSTRACT FROM AUTHOR]

Developing advanced underwater welding technology for titanium, which is the key structural material for underwater applications, is of great significance for the design, fabrication, and maintenance of submarine equipment. In this study, in order to investigate the underwater welding microstructure and mechanical properties of Ti-4Al-2V alloy, underwater wet laser welding was conducted on Ti-4Al-2V alloy using varying laser power. The microstructure and properties of the welding joints were characterized and analyzed. The microstructure of the heat-affected zone and fusion zone in the welding joints are not significantly different from those of welding in air, but a mixed oxide layer composed of Al2O3 and TiO2 is formed on the surface of the fusion zone. Due to internal stress, a large number of cracks initiate on the oxide layer and propagate to the joints. In the 4 kW and 5 kW joints, a penetrating crack formed due to the excessive accumulation of internal stress breaking up the α phase. The mechanical properties of the joints are significantly affected by the laser power. The tensile strength of the 3 kW and 4 kW joints is comparable to that of the base metal, which is about 600 MPa, while the 5 kW joint shows brittle fracture with no plastic deformation and 228 MPa strength. This research lays a solid foundation for understanding the underwater wet laser welding behavior of titanium alloys. [ABSTRACT FROM AUTHOR]

Metal inert gas (MIG) welding is widely employed for aluminum alloy welding, but high residual stress, coarse grain's structure, porosity, and micro-cracks occur during MIG welding. To avoid these defects, friction stir processing (FSP) was employed to the MIG welded joints of AA7075 and AA6082 with ER4043 filler. The grain structure of the weld fusion zone (WFZ) was categorized by eutectic precipitated Mg2Si, and primary α-Al. The elongated, coarse grain structure of the MIG weldment decreased after a one pass FSP. The Mg2Si precipitates were disseminated due to the enhancement of dispersion and dissimilar metal fraternization. The fraction area of the refined grains increases when the FSP pass increases. Furthermore, the effective enhancement of the joint efficiency was observed in the MIG + 4Pass FSP due to the grain refinement. The ultimate tensile strength (UTS) of 169.73 MPa of the MIG welded joint was observed with a grain size of 17.9 ± 0.3, while the highest UTS of 223.84 MPa was perceived at 4 passes of MIG + FSP joints with an elongation of 12.45%. The grain structure was also refined as the FSP pass increased, and the minimum grain size (2.6 ± 0.3 µm) was perceived at MIG + 4Pass FSP. Multipass FSP leads to refinement and homogenization of the microstructure, increasing the microhardness of the weldment. The average hardness value of the MIG weldments at the WFZ was 84 HV, while the microhardness of MIG + FSP joints of 1Pass, 2Pass, 3Pass, and 4Pass FSP was 88, 96, 101, and 110 HV at the stir zone (SZ). [ABSTRACT FROM AUTHOR]

Residual stresses can cause compromise in structural integrity; it is desirable to assess residual stresses using non-destructive testing so that effects on structural properties can be predicted. Electromagnetic (EM) sensors can be used to characterise residual stresses in steels accounting for, microstructure and geometry effects. Residual stress characterisation in welded EN S275 steel plates using EM sensors is reported. Low-frequency, low-magnetic field EM sensors were used to assess residual stresses in the plates. A finite element model for the sensor and sample was generated in COMSOL software so the influence of weld bead geometry and microstructure could be predicted and accounted for. This allowed residual stresses to be determined from EM sensor measurements, excluding the geometry and microstructure effects, XRD was used to verify EM sensor measurements. The highest residual stresses were found adjacent to the weld fusion zone, with magnitudes of, 170±5MPa, 120±20MPa and 42±10MPa for X-ray diffraction (XRD), a small EM sensor (U-12.7) and a big EM sensor (U-31) types, respectively. The differences are due to the volume of the material measured by each measurement type. It was shown that EM sensors are capable of measuring residual stress in welded plates to a good level of accuracy. [ABSTRACT FROM AUTHOR]

Resistance spot welding (RSW) was used to fabricate Similar joints of low-carbon steel AISI 1005 in lap joint design RSW. Evaluate the welding current, squeeze time, welding time, and hold time, which affects resistance spot welding. A tensile-shear force fracture test was used to assess the mechanical properties Using a universal tensile testing machine. The microstructure of the fusion zone was examined using a scanning electron microscope (SEM). According to the data, the shear strength values increased as the welding current increased. Additionally, it was shown that most failures occurred closer to the fusion zone (FZ). The primary cause is the crystal lattice's strained distortion, which weakens the nearby region of the fusion zone. [ABSTRACT FROM AUTHOR]

Crack-tip opening displacement (CTOD) tests were conducted on girth welds of two API 5L X70 pipeline steels (pipe A and pipe B) to investigate the influence of base metal composition on the fracture toughness of the joint. CTOD measurements across the weld showed that the weld fusion zone had the lowest CTOD values for both pipes, with pipe B having a higher CTOD value than pipe A. Detailed microstructure characterization of the multi-pass weld showed that the fusion zone in both pipes consisted of three distinct zones: the columnar zone, the coarse equiaxed zone, and the fine equiaxed zone. Both the columnar zone and coarse-grained equiaxed zone had acicular ferrite and grain boundary ferrite microstructures, whereas the fine-grained equiaxed zone had a finer ferrite microstructure compared to the other two zones. The main difference between the two pipes was the variation in ferrite grain sizes and the volume fractions of grain boundary ferrite and acicular ferrite. In comparison to pipe B, pipe A, with a higher concentration of Mo, Ni, and Cu in both the base metal and the weld fusion zones, consisted of a higher volume fraction of grain boundary ferrite and a lower volume fraction of acicular ferrite in the columnar and coarse-grained equiaxed zones. The lower concentration of Mo, Ni, and Cu in pipe B likely resulted in the formation of a predominantly acicular ferrite microstructure in the fusion zone, thereby improving the toughness of the weld joint in comparison to pipe A. [ABSTRACT FROM AUTHOR]

The article lists non-destructive testing (NDT)-related papers including "Update on ISO standards in condition monitoring and vibration," "AI for NDE 4.0--recent use cases," and "Principles for successful deployment of NDE 4.0."

This research investigates the hot corrosion behavior of Inconel 625 similar joints welded using pulsed current gas tungsten arc welding (PCGTAW). Specific emphasis has been given to the microstructural changes at the fusion zone and weld interface while employing two different Ni-Mo-rich fillers (ERNiCrCoMo-1 and ERNiCrMo-4). The microstructure of the weldments was evaluated using scanning electron microscopy (SEM) and optical microscopy (OM) techniques. The weld joints employed with ERNiCrMo-4 filler showed slightly higher strength than that of ERNiCrCoMo-1, and the fractures were found on the base metal regions. The performance of the alloy 625 bi-metallic joints has been ascertained by exposing both cyclic molten salt K2SO4 + 60% NaCl and an air oxidation environment at 700 °C. A thermogravimetric plot was employed to determine the weldment kinetics of corrosion. SEM/EDS systematically examined the oxide scales formed on the weldments, and x-ray diffraction (XRD) was used to identify the phases of the corrosion products. The test results revealed that the corroded samples in the salt condition experienced severe corrosion attacks as compared to air conditions by sulfidation and chlorination. Based on the specific outcomes of this study, ERNiCrMo-4 filler is recommended for joining these similar combinations of welds and it imparts better corrosion resistance at elevated temperatures in simulated boiler environments. [ABSTRACT FROM AUTHOR]

Theoretical models based on solutions of the conduction heat transfer equation have been widely proposed to calculate the thermal fields generated during laser welding, revealing simplification benefits and limitations in the accuracy of the results. In previous papers, the authors have introduced a parameterized analytical model based on the configuration of a virtual system of multiple mobile heat sources that simulates the effects of an actual keyhole welding mode by setting the system parameters so as to fit the calculated contours of the fusion zone in the weld cross-section of the experimental one. Even though a basic validation was already carried out by experimental detection, in order to further strengthen the model validity, this article deals with an extensive comparison between the results obtained by a multi-physics numerical simulation, performed by a commercial CFD software, and a theoretical one. The two different approaches were applied to the laser beam welding of butt-positioned AISI 304L steel plates. The investigation was focused on the effects of the keyhole on the main morphological features of the melt pool and fusion zone, and on the thermal fields obtained by the two models. The intrinsic differences between the two approaches, and how they are reflected in the corresponding results, were discussed. Satisfactory results were obtained by comparing the thermal fields, with a substantial convergence of the results, so as to validate the analytical model, assess the accuracy of its results, and define its application limits. [ABSTRACT FROM AUTHOR]

This paper investigated evolutions of α-Al sub-grains' morphology and crystalline orientation in the fusion zone during laser welding of 2A12 aluminum alloys. Based on this, a new method for assessing the weldability of materials was proposed. In laser deep-penetration welding, in addition to the conventional columnar and equiaxed dendrites, there also exhibited a corrugated structure with several 'fine-coarse-fine' transformations. In such regions, an abnormal α-Al coarsening phenomenon was encountered, with a more dispersed crystalline orientation arrangement and a decreased maximum pole density value. Particularly, structural alterations appeared more frequently in the weld bottom than the top. The above results indicated that the laser-induced keyhole presented a continually fluctuating state. Under such a condition, the solid–liquid transformation exhibited an unstable solidification front, a fluctuant undercooling, and a variational solidification rate. Meanwhile, the welding quality of this material is in a critical state to generate pores. Therefore, the appearance and relevant number of corrugated regions can be considered as a new way for judging the weldability, which will help to narrow the processing window with better welding stability. [ABSTRACT FROM AUTHOR]

Intermediate transformation structures in the fusion zone of a weld joint of the X80 steel plates 8 mm thick are studied. It is shown that laser welding leads to the formation of predominantly bainite structures of various types and a small fraction of martensite in the fusion zone. The microhardness measurements in different structural phases have been carried out. The fine bainite and martensite structures have been analyzed using scanning tunnel microscopy. [ABSTRACT FROM AUTHOR]

Numerical modelling of laser welding requires that numerous strongly coupled physical phenomena be taken into account. A laser is a source of welding heat characterized by the small size of the heating volume and the shape of the fusion zone has a marked impact on the quality of the weld. In this work, a conical heat source was used with geometrical parameters to give the appropriate profile of the fusion line. The use of the weld shape factor and the dependence of the power density on the linear welding energy increases the accuracy of matching the calculated shape of the fusion line. The heat source was tested for the continuous welding case of a sheet made of steel type S355J2. The CFD software ANSYS Fluent was used to calculate the welding model. The temperature field, calculated using the finite volume method, was used to calculate the phase composition and fusion zone profile tracking. The nodes of the model reaching the maximum solidus temperature of S355J2 steel, form the profile of the fusion zone. The laser welding model allows for tracking of the kinetics of phase transformations in the cooling stage. Continuous cooling transformation phase diagram data is loaded for the welded steel grade. The calculation results of the welding model were compared with the weld micrographs. [ABSTRACT FROM AUTHOR]

316L stainless steel joined to mild steel is widespread in several applications to reach a requested good association of mechanical properties at a lower cost. The activating tungsten inert gas (ATIG) weld was carried out using a modified flux composed of 76.63% SiO2 + 13.37% Cr2O3 + 10% NaF to meet standard recommendations in terms of limiting the root penetration. Modified optimal flux gave a depth of penetration 1.84 times greater than that of conventional tungsten inert gas (TIG) welds and a root penetration of up to 0.8 mm. The microstructure of the dissimilar joints was investigated using a scanning electron microscope and EDS analysis. The mechanical properties of the weld were not affected by the modified flux. The results show that the energy absorbed in the fusion zone in the case of ATIG weld (239 J/cm2) is greater than that of TIG weld (216 J/cm2). It was found that the weld bead obtained with the optimal flux combination in ATIG welding can better withstand sudden loads. The obtained UTS value (377 MPa) for ATIG welding was close to that of TIG welding (376 MPa). The average Vickers hardness readings for ATIG welds in the fusion zone are up to 277 HV, compared to 252 HV for conventional TIG welding. [ABSTRACT FROM AUTHOR]

Alloy 800 was subjected to an autogenous welding treatment using two varying techniques, laser beam (LB) welding and tungsten inert gas (TIG) welding. The weldment regions such as weld fusion zone (WFZ), heat-affected zone (HAZ) and base metal were compared using reactivation technique, i.e., double loop electrochemical potentiodynamic reactivation (DL-EPR) test and ASTM G 28 test for intergranular corrosion (IGC) susceptibility. Alloy 800 showed no significant DOS values in WFZ of laser weldment as cooling rates were faster resulting in negligible carbide precipitation and chromium depletion which was ascertained by G28 test. While considerable reactivation was observed in HAZ of TIG and LB weldments as they are exposed to carbide precipitation temperatures during welding procedures as a result of heat input and cooling rates. Magnetic susceptibility measurements on weldments indicated extent of chromium depletion. The DOS values measured for Alloy 800 LB weldments were one order of magnitude less for all regions as compared to TIG weldment and corroborated with depth of attack obtained from IGC tests. The highest DOS values were observed for HAZ of TIG weldment. DOS values are an indirect measurement of chromium depletion in HAZ that will weaken the passive film formation and result in increased corrosion in ASTM G28 test. The increased grain boundary attack and grain dropping suggest decreased IGC resistance of Alloy 800 weldments by TIG welding compared to LB welding. Hence, laser welding technique is a better technique for welding/repair welding of SG tubes to avoid sensitization and reduce its susceptibility to intergranular corrosion/intergranular stress corrosion cracking (IGC/IGSCC) during operations. [ABSTRACT FROM AUTHOR]

The failure of resistance spot welds through the fusion zone along the sheet/sheet interface (i.e., interfacial failure) is critical for automotive crashworthiness. This paper investigates the effect of fusion zone hardness on the interfacial failure behavior of resistance spot welds during the tensile–shear test. AISI 1040 medium carbon steel, producing a high level of hardness mismatch during resistance spot welding, was selected as the base metal. By ex situ tempering heat treatment, various levels of fusion zone hardness are achieved in the welds with constant fusion zone size. It is shown that the interfacial failure of the spot welds is a competition between ductile shear failure and rapid crack propagation. It is found that there is a critical fusion zone hardness beyond which the interfacial failure mechanism transitions from ductile shear failure to rapid crack propagation. In welds with high fusion zone hardness, the mechanism of interfacial failure is rapid crack growth, and fusion zone fracture toughness is the governing factor for the interfacial failure load. Conversely, in welds with low FZ hardness, the mechanism of interfacial failure is a ductile shear failure, and fusion zone hardness would be the governing factor for the interfacial failure load. [ABSTRACT FROM AUTHOR]

In this paper, 2205 DSS sheets with equal amounts of ferrite and austenite joined by GTAW, GMAW1 (equal welding speed with hybrid welding), GMAW2 (equal input heat with hybrid welding), and hybrid GTAW-GMAW. Then, heat distribution, maximum temperature, and cooling time during welding obtained from finite element simulation and the results were validated. Finally, the effect of input heat, cooling time, and welding method condition on quality and final microstructure of the joint were investigated. In addition to having a very good appearance, hybrid welding also has the highest ratio of weld depth to weld width. Also, due to the effect of using two arcs, on a same input, it has a lower maximum temperature comparing GMAW2. The average cooling time in hybrid welding is 26.5 s, which is less than GMAW2 and more than GTAW and GMAW1, and this has caused the weld metal microstructure to have approximately equal amounts of ferrite and austenite (48% austenite). This has caused the hardness of the weld zone in hybrid welding to be higher than the hardness of GMAW2 and close to the hardness of GTAW. Microstructural studies also revealed that the main morphology of austenite in fusion zone of hybrid welding is Widmanstatten. The size of ferrite grains in HAZ for hybrid welding is 204.3 μm, which is smaller than GMAW2 and larger than GTAW and GMAW1. The reason for this is the shorter cooling time in hybrid welding compared to welding GMAW2. [ABSTRACT FROM AUTHOR]

The present work investigated the microstructural feature, mechanical properties, and residual stress variation for the dissimilar welded joints (DWJs) of P92 and AISI 304L steel. The multi-pass DWJs were attempted for narrow gap geometry using the tungsten inert gas (TIG) welding process employing the ERNiCrMo-3 filler metal. The martensitic microstructure produced in the P92 HAZ region after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for a period of 2 h to get tempered martensitic microstructure and re-precipitation of dissolved precipitates. The radiographic examination and macrostructure analysis showed defect-free P92/304L SS DWJs. The weld metal showed the complete austenitic microstructure with a Ni weight percentage of 36%. However, segregation of the alloying elements along with the inter-dendritic areas and variation in grain growth during solidification was observed. There is columnar grain morphology at interface, cellular, and equiaxed in the center. The major segregation along the inter-dendritic areas was observed for Nb, Mo, Ti, and Cr that led to the formation of the carbides of type Mo6C, TiC, and NbC, which was confirmed from the energy dispersive spectroscopy (EDS) analysis. From the tensile test result, 304L SS base metal (BM) was inferred as the weakest region in P92/304L SS DWJs. The ultimate tensile strength (UTS) of the as-weld joint was about 626 MPa, along with fracture location in 304L SS base metal. The Charpy impact test results showed that the region with relatively poor impact toughness was austenitic ERNiCrMo-3 filler weld (57 J) which might be due to the segregation of the Nb and Mo along the inter-dendritic areas. However, the impact toughness of the ERNiCrMo-3 filler weld met the minimum requirement of 47J (EN ISO 3580:2017). The micro-hardness result showed that in the as-welded condition, the coarse grain heat affected zone (CGHAZ) has the highest micro-hardness value (340 HV) due to the high weight percentage of Cr and N resulting from the dissolution of M23C6 precipitates followed by the fine grain heat affected zone (FGHAZ, 270 HV), and the inter-critical heat affected zone (ICHAZ, 205 HV). After PWHT, the hardness value was decreased below the maximum allowable value of 265 HV due to the tempering of the martensite. The residual stresses developed in the case of the narrow groove design were less due to the less quantity of weld metal available for volumetric contraction in the case of the narrow groove geometry. The tensile stress was dominant in the weld fusion zone due to the volumetric contraction of the weld metal, while compressive stress was dominant in P92 HAZ because of the martensitic phase transformation. [ABSTRACT FROM AUTHOR]

Grade P92 steel has a possibility of forming delta (δ) ferrite phase in the weld fusion zone, which has several detrimental effects on mechanical properties. This study investigates the effect of preheating temperatures on the retention of δ-ferrite in Grade P92 steel welds. A relation between preheating temperature and thickness of welded plate using Rosenthal 2-D heat equation was developed, which can predict the preheat temperature for a given thickness of thin plates to achieve the full penetration. The welded joints were made using different preheating temperatures and with a fixed heat input using autogenous tungsten inert gas welding. Thermo-Calc software was used to predict phases formed as a function of temperature and for Scheil's solidification calculation. A DICTRA diffusion model was used to predict the volume fraction of δ-ferrite for different preheating temperatures. Full penetration was achieved with a preheat temperature of 300 °C for a 6 mm plate thickness. As preheating temperature is increased the volume fraction of δ-ferrite is reduced. The δ-ferrite retention is overestimated by DICTRA as compared to the retention measured experimentally from micrographs. [ABSTRACT FROM AUTHOR]

Welds of polymer materials, butt welded with a heated tool, are distinguished by a variety of structural components. Investigations of such welds allow studying the general fundamental processes of structure formation in the formation of welded joints of polymers. In this work, mechanical tests of welded joints of polymer pipes with a local load in the environment of surface active substances and with the use of the Rehbinder effect were carried out. Experimental specimens of pipe joints with a diameter of 63, 90, 110 and 160 mm from pe80 polyethylene were produced in the standard equipment for butt welding with a heated tool on the modes recommended by DBn v.2.5-41:2009. the tests were carried out in accordance with the requirements of the international standard ISO 22088 "Cracking under the influence of the environment" (ESC). The characteristic features of cracks propagation in the tests of the base material and the fusion zone of the weld were investigated. using optical microscopy, the fracture surfaces of the specimens were investigated immediately after tests and after chemical etching in sulfuric acid solution. It was shown that in the fusion zone, a weakened "blurry" structure of polymer material is formed, which is fractured during a local load. [ABSTRACT FROM AUTHOR]

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In this study, we present the results from electron-beam welding operations applied on copper and Al6082T6 aluminum alloys. The influence of beam-scanning geometries on the structure and mechanical properties of the welded joint is studied. The experiments were conducted using a circle oscillation mode with an oscillation radius of 0.1 mm and 0.2 mm. The beam deflection was set to 0.4 mm with respect to the side of the aluminum alloy, and the beam power was set at 2700 W. The phase composition of the obtained welded joints was studied by X-ray diffraction (XRD). Scanning electron microscopy (SEM) was used for the investigation of the microstructure of the joints. The chemical composition was investigated by using energy-dispersive X-ray spectroscopy (EDX). The mechanical properties were studied by micro-hardness investigations. The fusion zone of the weld seam contains three phases—an aluminum matrix, an ordered solid solution of copper and aluminum in the form of CuAl2, and pure copper. Electron beam-scanning geometries have significant influences on the structure of the weld. Increasing the beam oscillation's radius leads to a decrease in intermetallic phases and improves homogeneity. The measured microhardness values in the fusion zone are much higher than the ones measured in the base metals due to the formation of intermetallic phases. The microhardness of the weld joint formed using an oscillation radius of 0.2 mm was much lower compared to the one formed using an oscillation radius of 0.1 mm. [ABSTRACT FROM AUTHOR]

With advancements in the automotive industry, the demand for electric vehicles (EVs) has remarkably increased in recent years. However, the EV battery, which is a vital part of the EV, poses certain challenges that limit the performance of the EVs. The joining of dissimilar materials for different components affects the electrical and mechanical performances of EV batteries. Laser beam welding is a promising technique for joining Al and Cu for application in secondary battery fabrication because of the precise control over heat input and high process speed. However, the production of Al–Cu joints remains challenging because of the differences between their thermal and metallurgical properties and the resulting formation of brittle and hard intermetallic compounds, which reduce mechanical and electric properties. Thus, it is vital to characterize the weld to improve joint performance and enhance the laser welding process. This study investigates the joining of an Al alloy (AA1050) with Ni-coated Cu using a continuous-wave Yb fiber laser. The evaluation of the weld morphology showed a correlation between the weld characteristics and process parameters (laser power and welding speed). The weld interface width and penetration depth into the lower sheet (Cu) both increased with increasing heat input. Optical microscopy of the weld cross-section revealed many defects, such as voids and cracks. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) was employed to examine the weld microstructure. The composition analysis revealed the presence of mixed morphology of Al–Cu eutectic alloy (α-Al+Θ-Al2Cu) phase in the form of dendrites in the weld fusion zone with traces of the highly brittle Al4Cu9 phase at a high heat input condition. Furthermore, the electrical contact resistance of the weld seam was measured to determine the correlation between heat input and resistance. In addition, Vickers microhardness measurements were performed on the weld cross-section to validate the SEM/EDS results. [ABSTRACT FROM AUTHOR]

This study ascertains a three-dimensional (3D) numerical modeling employing hybrid conical-cylindrical heat source concerning the heat transfer, molten fluid flow weld pool dynamics, and cooling rate phenomena associated with the laser weld pool of 316 LN stainless steel (SS) by computational fluid dynamics. The heat source interprets the transmission of laser energy to the substrate by accounting for recoil pressure and surface tension effect using the multiphase flow modeling. The impact of laser power for a constant welding speed on the penetration depth is predicted to select an optimized laser energy input to carry out full penetration laser welding experiment. The model pictures the depth of penetration, temperature distribution, velocity field, and weld pool flow pattern and keyhole behavior for the optimized welding condition. Non-dimensional heat transfer entities such as Peclet and Marangoni numbers are also assessed that provide insight related to the thermal-fluid flow mechanism and final weld fusion zone attributes of the 316 LN SS laser weld. The simulated model agrees well with the experimentally achieved full penetration laser weld giving fair concordance with the weld bead dimensions and thermocouple measurements. The model has been used to calculate the secondary dendritic arm spacing in the fusion zone. Calculated values were in agreement with the measured values. The numerical outcomes recognize that the hybrid conical-cylindrical heat source model is well suited for predicting weld peak temperature, weld pool velocity, weld pool dynamics, weld pool shape, and cooling rate for the laser welding of 316 LN SS. [ABSTRACT FROM AUTHOR]

Higher heat input rates and uneven thermal cycles involved in fusion welding processes effect HAZ properties and causes to develop residual stress across fusion zones. These thermal stresses reduce the service life of welded structures. To understand the thermal cycles, In-Situ peak temperatures and their distribution over the weld surface of similar and dissimilar combinations of Monel 400 and AISI 316 base plates joined by constant and pulsed current TIG welding processes are measured with Infrared thermography technique at different time intervals. After welding the joints, thermal stresses developed across the joints were measured using X-ray diffraction technique. The stress measurements were made on weld surfaces of fusion zone and HAZ on either side of base metals. Higher temperature values were recorded during constant welding technique than the pulsed welding technique. Also, the heat affected area was more in weldments of constant welding technique. The maximum temperatures of 1657 0C, 1711 0C and 1748 0C were recorded in CCGTAW process during pass-1, pass-2 and pass-3 welding, respectively. Whereas, in PCGTAW process, maximum temperatures of 1434 0C, 1509 0C and 1634 0C were recorded during pass-1, pass-2 and pass-3 welding, respectively. The overall reduction in temperatures in PCGTAW process was 10.6%, which could affect the cooling cycles during solidification. Both the welding techniques have exhibited development of compressive natured residual stresses in dissimilar joints. The heat concentration at fusion area was reduced in pulsed technique that resulted in lower residual stresses. [ABSTRACT FROM AUTHOR]

The presented study intends to analyze the microstructure and corresponding mechanical characteristics of P91 and Incoloy 800HT dissimilar welded joint (DWJ). The thermo-physical property differences between P91 and Incoloy 800HT arise due to their complex alloying composition, making their weldability difficult. Incoloy 800HT is difficult to weld due to its high susceptibility to solidification cracking. The recommended nickel-based filler metals for welding Incoloy 800HT were employed to weld P91 and Incoloy 800HT using conventional gas tungsten arc welding (GTAW). The welded joint morphology and characteristics were analyzed in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The PWHT was performed to observe changes in microstructural inhomogeneity and residual stress relaxation in weld after the heat treatment. An electron probe microanalyzer (EPMA) was utilized to observe the distribution and segregation of elements in different weld regions. The deep hole drill technique was employed to find the distribution of bi-axial residual stresses in the weld fusion zone (WFZ) and heat-affected zone (HAZ) of base metals in both AW and PWHT conditions. The two nickel-based fillers, ERNiCr-3 and ERNiCrMo-3, were employed, and their weld characteristics were compared. The mechanical strength of ERNiCr-3 filler-based DWJ was found superior to ERNiCrMo-3 filler-based DWJ. The standard AW and PWHT ERNiCr-3 filler-based DWJ tensile specimen failed from Incoloy 800HT base metal with an ultimate tensile strength (UTS) of 570 ± 4 MPa and 650 ± 4 MPa, respectively. The ERNiCrMo-3 filler-based DWJ obtained the highest UTS of 679 MPa after PWHT in a subsize specimen. The microhardness for ERNiCrMo-3 WFZ was found to be higher than ERNiCr-3 WFZ microhardness, and PWHT successfully tempered the P91 HAZ. Further, the impact toughness for the ERNiCr-3 WFZ in AW condition was 86 ± 3 J and PWHT did not provide any significant improvements, while ERNiCrMo-3 WFZ had an impact toughness of 47 ± 10 J in AW state and 41 ± 10 J in PWHT state. Thus, a successful weld characteristic study of defect-free P91 and Incoloy 800HT DWJ was completed, and ERNiCr-3 filler was concluded to be an optimum choice of filler to make the DWJ between P91 and Incoloy 800HT. • Dissimilar weld joints of P91 steel and Incoloy 800HT alloy were investigated for microstructure and mechanical properties. • Through thickness residual stress measurement along the weldments ware performed using the deep hole drilling method (DHD). • Gradient microstructure at the ErNiCr-3 filler welds and P91 steel interface was clarified using the SEM and EPMA methods. • Effect of the post-weld heat treatment (PWHT) on microstructure, mechanical properties, and residual stress variation along the weldments were performed. [ABSTRACT FROM AUTHOR]

• Four ODS steel electron beam welds were made using different traverse speeds of the beam. • The weld zone was widest in the weld with the highest input, but microstructural features were similar in all welds. • The welds have a coarse columnar grain structure adjacent to the fine grains of the base material. • The weld zone had a hardness of ∼30 % less than the base material. • Yttria-based oxides are significantly coarsened after welding. This work investigated the impact of electron beam (EB) welding, using various traverse speeds of the electron beam (1200–2200 mm/min), on the microstructure of PM2000 ODS steel which was characterized using analytical electron microscopy and microhardness. The different heat inputs during welding explored in this study (72–39 J/mm), related to the traverse speed used, correlated with small differences in the widths of the fusion zone. Only minor differences in local microstructures and hardness of the fusion zones were detected amongst the four butt welds produced. The fusion zone is characterized by large columnar grains in the ferritic matrix, together with a coarsened Y-Al-O particle distribution and a reduction in its particle number density as compared to the base material. There is also a sharp border between the fusion zone and base material, with the joint showing little evidence of a heat-affected zone. These changes in microstructure during welding led to a hardness reduction of ∼30 % in the fusion zone of the welds with respect to the base material. [ABSTRACT FROM AUTHOR]

During dissimilar steel welding, differences in magnetic permeability and thermophysical parameters between materials result in significant disparity in heat distribution on both sides of weld and poor weld formability. To solve the welding quality problems caused by significant disparity in heat distribution, a novel composite magnetic field consisting of longitudinal magnetic field (LMF) and cusp magnetic field (CMF) is applied to dissimilar steel welding. In this study, the influence of novel magnetic field on the mechanical characteristics, microstructure, and weld formation of dissimilar steel gas tungsten arc welding (GTAW) welds was investigated. It was found that arc deflection is influenced by both the material properties and LMF. When longitudinal exciting current (I L) was 0.5A, the weld melting zone tended to be symmetrical. On the premise that I L remained unchanged at 0.5A, as cusp exciting current (I C) increased from 0A to 5A: the weld fusion zone always remained symmetrical; The arc compression degree, weld penetration, melting area of weld and weld penetration/width ratio significantly increased, while the weld width progressively reduced; The heat-affected zone's (HAZ) width of the base metals and the mean grain size in the HAZ are significantly reduced; The mean microhardness of the weld metal (WM) and tensile properties are also significantly improved. The study results enrich the research foundation on heat input regulation in dissimilar steel GTAW, providing experimental evidence and theoretical support for resolving welding quality issues caused by welding conditions with different material properties. • Novel composite magnetic field can regulate heat input distribution and arc heat flow density. • Novel composite magnetic field optimizes weld formation of dissimilar steels. • Novel composite magnetic field promotes grain refinement in HAZ. • Novel composite magnetic field reduces the thickness of the transition zone at WM/BM interface. [ABSTRACT FROM AUTHOR]

Application of additively manufactured steels is unavoidably involved in the resistance spot welding with conventionally manufactured steels. However, the microstructural evolution of an additive manufactured steel at high temperatures is still unknown, especially for the rapid solidification process. This paper investigated the microstructural evolution of a selective laser melted maraging steel during the rapid solidification process via resistance spot welding. Asymmetrical fusion zone with boat shape was found in the spot weld due to the rougher surface and larger electrical resistance of maraging steel via selective laser melting (SLM) process. The rapid expansion of fusion zone at end of welding process was caused by the carbide formation at the heat-affected zone of maraging steel via selective laser melting process. Besides, printing orientation affected the surface roughness of a selective laser melted maraging steel and subsequently significantly influenced the early stage of formation of fusion zone of additively manufactured maraging steel. We expect that our findings will pave the way to the future application of additively manufactured steels in the industries. [ABSTRACT FROM AUTHOR]

The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively. [ABSTRACT FROM AUTHOR]

Inconel alloys are used for high temperature applications due to their excellent properties at elevated temperatures. The joining of Inconel alloys with other alloys is challenging due to the formation of cracks and interface microstructural segregation of alloying elements. In the present investigation Inconel 718 alloy was joined with high tensile steel using laser welding. In order to attain the quality joints, welding parameters were studied and identified their range. The microstructural characteristics of the welds at the fusion zone and heat-affected zone were analyzed. The microhardness variations across the fusion zone and other zones were observed. The mechanical properties of the joints were evaluated and found that the strength of the joints was related to laser power. The elemental analysis across the fusion zone was revealed the formation of segregation of the elements which has an influence on the strength of the joints. [ABSTRACT FROM AUTHOR]

The effect of high-frequency mechanical peening conditions on the fatigue resistance of 3sp steel butt weld joints was studied. Different techniques of preparing test specimens offered a conclusion that the quantitative contribution from residual compression stresses, strain hardening of the surface layer of the groove formed after peening of the narrow zone of weld fusion with the base metal, and stress concentration variations to the enhancement of the endurance limit of weld joints makes up 57, 37, and 6%, respectively. The groove depth was shown to correlate with the depth of a plastically strained material layer. The procedures were advanced to evaluate the endurance limit of butt welds after different conditions of peening in the groove depth and plastically strained material layer under its bottom, using experimental data on the microhardness measurement depth, as well as in an examined range of variations of the tool vibration amplitudes. The groove depth against the travel speed and peening tool vibration amplitude, as well as endurance limit variations after different production techniques, were established. With the peening speed irrespective of the tool vibration amplitude, the efficiency of increasing the fatigue resistance of weld joints was shown to decrease, at a speed of 0.4 m/min, the endurance limit increases by 11% due to strain hardening, and the total effect of all the factors typical of peening results in its 26% growth. [ABSTRACT FROM AUTHOR]

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The present study investigated the influence of welding speed on the microstructure, hardness, and tensile properties of the AZ31 Mg alloy gas tungsten arc (GTA) welds that were prepared using alternating current (AC). A microstructural examination of the weld metal and base metal was performed using stereo, optical, and scanning electron microscopy (HR-SEM and EDS) techniques. The microstructure of all fusion zones consists of two parts: a columnar zone, adjacent to the fusion boundary, and equiaxed grains, in the centre of the weld fusion zone. It is shown that the average width of the equiaxed zone present at the centre of the fusion zone increases with increasing welding speed. Metallographic examination shows that the highest welding speed (5 mm/s) results in the smallest average grain size. The welds prepared with high welding speed exhibit an increase in strength, hardness, and ductility compared with other welding speeds, which is attributed to low heat input. [ABSTRACT FROM AUTHOR]

Duplextubes are widely used in oil and gas storage and transportation, the nuclear industry, and other fields, but the welding quality of metals is an important factor affecting the use of equipment. In order to study the welding quality of S10C steel/Incoloy 825 duplextubes and Q345R tube sheet based on gas tungsten arc welding technology with a filler of ER50-6 carbon steel welding wire, the microstructure and grain size of fusion welding zone of duplextubes and tube sheet under welding currents of 150 A, 160 A, and 170 A were studied by optical microscopy and scanning electron microscopy. At the same time, the corrosion behavior of fusion welding zone after the welding was investigated in 3.5 wt.% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the metallurgical structure of the fusion welding zone was mainly composed of δ-ferrite and retained austenite. The grain size in the fusion welding zone increased with the increase of the welding current. The corrosion resistance of the fusion welding zone welded with a high welding current of 170 A was better than that with low welding currents. However, the pitting corrosion resistance of fusion welding zone with the lowest welding current of 150 A was better than that with high welding currents. This study can provide a preliminary exploration for the manufacture and applicability of duplextubes air coolers. [ABSTRACT FROM AUTHOR]

A new class of W-free, precipitation strengthened Co-base superalloys has recently been developed with improved high-temperature strength while maintaining excellent oxidation and hot corrosion resistance. In this study, we report the impact of fusion welding on microstructure and properties of an alloy of this class having a nominal composition Co–30Ni–10Al–5Mo–2Ta–2Ti. We carry out bead-on-plate laser welding of the plates and characterize the microstructure and properties of the welded samples. Fusion zone of the welds consists of FCC γ dendrites and an interdendritic network of ordered γ ′ phase. Finer γ ′ precipitates are observed inside γ dendrites, which form by solid-state transformation during post-solidification cooling. Measurement of phase compositions reveals differences in solid/liquid partitioning behavior of the constituent elements and indicates significant solute trapping for Mo, Ti, and Ta. Experimentally determined partition coefficients for Co and Ni agree reasonably well with thermodynamic predictions obtained using Thermo-Calc, but the prediction for Al contradicts the observations. Although welding-induced microstructural changes lead to a drop in the hardness, it was successfully restored after a post-weld solutionizing-aging treatment. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) are a novel class of materials that represent an evolution of common engineering alloys to a wider array of compositional and properties possibilities. As such, the exploration of methodologies to achieve improved microstructure and mechanical characteristics of these materials for potential applications in industry is a requirement that is experiencing extended research efforts. One example of a processing method able to expand the potential applications of these alloys is Gas Tungsten Arc Welding (GTAW), which allows to evaluate the metallurgical evolution and corresponding mechanical performance, associated to the impact of a localized heat input on the material. However, GTAW and related fusion-based welding processes are known to generate large grain sized-structures in the fusion zone, which often is detrimental to the joint performance. Thus, the integration of high temperature inoculant particles on the fusion zone during welding is a potential way to improve this region's microstructure and, therefore, its mechanical performance. In this work, we discuss the effect that the addition of TiB 2 micron-sized particles have on the microstructure of a GTAW AlCoCrFeNi-based HEA. For this, the microstructure of the welds was evaluated by means of optical and electron microscopy, synchrotron X-ray diffraction and CalPhaD-based simulations. Mechanical testing was performed using microhardness mapping and tensile testing coupled with digital image correlation. The results evidenced that successful inoculation with TiB 2 proved capable of altering the microstructure of the fusion zone (FZ), refining it. Nevertheless, preferential deformation in the relatively softer heat affected zone during tensile testing resulted on premature failure of the inoculated joints, due to the concomitant higher hardness of the FZ. [Display omitted] • Gas tungsten arc welding was successfully used for joining an AlCoCrFeNi high entropy alloy. • Addition of TiB 2 to the fusion zone influenced grain structure and local mechanical properties. • Microstructure and mechanical characterization aided by thermodynamic modelling unveil the role of TiB 2 particles. • Mechanical properties of AlCoCrFeNi joints depends on the selection of inoculant particles and fraction. [ABSTRACT FROM AUTHOR]

The work is devoted to study of the influence of process parameters of welding steel 20 on the structure and properties of low carbon steel welded joints. Experimental steel was modified by nanosized carbide modifier of the system of «thermally split graphite (TRG)–wolframite». The aim of the study was to establish the details of formation of the structure and complex of mechanical properties in the material, containing dispersed reinforcing particles of the carbide phase under the thermal influence of welding processes. The steel was obtained by the method of electron beam remelting (EBR) of the charge billet, which included a nanoscale carbide modifier. Welding of experimental steel samples was performed using electron beam welding (EBW) and argon-arc welding (AAW) technologies. The obtained samples were used to study the macro- and microstructure of the base metal and welded joints by optical microscopy, as well as to determine the mechanical characteristics of metal of welded joints. It was found that the base metal, produced by EBR and following hot rolling of the obtained ingot has a homogeneous ferritic-pearlitic structure, but the morphology of the carbide phase in eutectoid colonies differs from plate pearlitic morphology due to the presence of spheroidized carbide phase particles. In welding by AAW technology, structures with the morphology of the same type as in the base metal are formed in the HAZ, the main difference is the increase in the degree of carbide phase spheroidization and some increase in grain size. EBW technology leads to formation of narrow layers with the structure of lath martensite in the weld fusion zone. It has been established that both the welding technologies provide joints with mechanical characteristics on the level of the base metal, but the EBW technology ensures higher ductility characteristics of the metal. Ref. 13, Table. 4, Fig. 7. [ABSTRACT FROM AUTHOR]

Creep rupture behavior of dissimilar weldments between FB2 and 30Cr1Mo1V heat-resistant steel by multipass welding at 783 K (510°C) under different stresses (260 to 420 MPa) was researched. The fitted creep rupture exponent is 14.53, and the 10,000 h extrapolating strength values predicted by the power law and Larson-Miller parameter show good agreement with experimental data. The samples exhibit a ductile fracture character and fracture in the weld fusion zone, which has a highly heterogeneous microstructure and grains with different morphologies and sizes and an obvious softening. There exist a decrease in the dislocation and precipitate density and an increase in the subgrain size in the weld metal after creep. The rupture is a transgranular fracture characterized by dimples as a result of microvoid coalescence. Laves phases along with copper-rich precipitates are observed in the vicinity of fracture surface, which creates a stress concentration that can cause transgranular fracture initiation. [ABSTRACT FROM AUTHOR]

A three-dimensional finite-element thermal model with a volumetric moving heat source is developed to simulate the gas tungsten arc welding process of a newly developed cobalt-based superalloy, CoWAlloy1. The model shows that the geometry of the molten weld pool can be significantly influenced by the welding speed. A numerical analysis is conducted with the model to calculate the cooling rate, thermal gradient, and solidification growth rate at various regions of the fusion zone for different welding speeds. The cooling rate is found to increase from the weld fusion boundary to the centreline region of the FZ at all welding speeds. A columnar-equiaxed microstructure is formed at the centreline of the FZ region and the extent of the columnar microstructure is reduced with an increase in the welding speed. Therefore, a high welding speed facilitates the formation of a fully equiaxed grain structure in the FZ of the alloy. Experimental work with CoWAlloy1 is used to validate the theoretical predictions made by the model and a good agreement is found between the experimental and modeled results, which confirms the robustness of the model used in this study. [ABSTRACT FROM AUTHOR]

The present work reports about the effect of cast scandium doped ER5356 filler rod in Tungsten Inert Gas welding of dissimilar Aluminium Magnesium alloys. The grain refinement effect on weld microstructure by transition metal scandium was investigated with optical and scanning electron microscope. Additionally, XRD analysis, tensile strength (global and component joint) and microhardness were tested on weld samples. The microstructural examination in weld fusion zone observed fine grain size and suppressed dendrite arm spacing. The formation of Al3Sc precipitate in weld fusion zone due to scandium inclusion in filler was identified and resulted in improving the weld strength significantly. The higher joint efficiency of 92.5% was achieved in the global joint of weld samples. The failure location of global joint tensile samples identified the weld fusion zone is stronger than AA5052 base material. Further weld strength was evaluated with component joint by micro tensile test, which results in 70MPa enhancement in UTS values and validating the accurate weld strength. However, the elongation of the tensile test sample reduced marginally for the weld. The fracture mechanism of the weld joint observes decrease in ductility. The significant increase in hardness of the weld fusion zone was evident due to doping of scandium compared to the other zones of the weld. [ABSTRACT FROM AUTHOR]

This research work aimed to observe the creep behaviors of the ASTM A36 welded joints. The microstructure and hardness of the base zone (BZ), heat affected zone (HAZ), and weld fusion zone (WFZ) were measured. Afterward, the residual stresses on the welded plate were observed to determine any lead to fatigue failure. The hot tensile tests were then performed to investigate the welded specimens' creep behaviors at varied strain rates and temperatures. The power-law model was applied to describe the creep behaviors at each testing condition. Finally, the scanning electron microscopic (SEM) images of the tested specimens were observed to identify breakage causes. The creep results showed that the weakest locations were found in the base (A36) zones. The areas prone to ductile fracture was the base zones close to HAZ. [ABSTRACT FROM AUTHOR]

The present study investigates susceptibility of Inconel 617 to liquation cracking in laser-based welding techniques such as autogenous laser welding (ALW) and laser-MIG hybrid welding (LHW) with variation in heat input. Advanced characterization techniques such as high-speed Nano-Indentation testing and micro X-ray diffraction techniques were utilized to analyze microstructural variations in correlating mechanical behavior of low-melting eutectics formed in partially melted zone (PMZ). Results indicated that the liquation cracking in PMZ was associated with the constitutional liquation reaction between intermetallic carbides and austenite matrix. With increase in heat input, its susceptibility reduced, although with enhancement in grain-boundary liquid film formation and was associated with the constitutional liquation of (Cr, Mo)-rich M23C6 carbides and γ matrix. Combined effect of induced thermal stress with presence of low-melting eutectics in partially melted zone was found to greatly influence liquation-cracking susceptibility in both the welding processes. Indeed, ternary eutectic comprising metallic carbides of Cr and Mo and austenite-matrix with low nano-hardness values compared to that of hard carbides present in base metal and weld fusion zone re-confirmed their influence on cracking susceptibility. Increase in heat input enhanced dissolution of Mo-rich M6C carbides that attributed to stress-relaxation and thereby reduce cracking propensity. [ABSTRACT FROM AUTHOR]

This paper has proposed a parameter estimation method for a laser welding process inherently highly nonlinear as a result of the highly nonlinear inputs and outputs of the system. Hence, a nonlinear system identification method was developed for the laser welding process using the wavelet network nonlinear autoregressive exogenous (ARX) model. The advantage of ARX over the standard nonlinear models is that it not only considers the delayed input and output regressors but also uses nonlinear functions for mapping, thus making ARX a better candidate for the prediction of nonlinear behaviors. In total, nine available datasets for the training and test phases at pulse durations, pulse frequencies, focal lengths, currents, and welding speeds were considered. Five inputs including pulse duration, pulse frequency, focal length, current and welding speed, and temperature as one output were considered. The first eight datasets were utilized for the training phase and one was used for the testing phase. The results showed that the ARX model had an acceptable performance in training and test phases, and it was capable of identifying the nonlinear and time-variant phenomenon of the laser welding process examined in this paper. For instance, most fitness values for austenitic and ferritic steel samples in the training time histories were 97.13 and 97.95, respectively. [ABSTRACT FROM AUTHOR]

• A welding strategy exploiting laser beam oscillation and in-situ alloying was proposed to obtain ultra-fine equiaxed grains. • The periodical fluctuation of molten metal induced by the oscillating laser beam facilitated diffusion of Zr elements. • The tensile strength of the welded joints increased by 66 %, from 228 to 379 MPa The formation of weld cracking in high-strength Al-Li alloys has been a longstanding challenge attributed to undesirable coarse columnar grains and inhomogeneous microstructure distribution in the fusion zone of welds. At present, grain refining has been recognized as the most effective approach to inhibit cracking and enhance the mechanical properties of welded joint. Herein, a novel welding strategy exploiting laser beam oscillation and in-situ alloying with Zr was proposed to obtain ultra-fine equiaxed grains in all-weld metal for medium-thick Al-Li alloy. Macro-scale simulation for heat-mass transfer and micro-scale simulation for microstructure evolution were conducted to investigate the formation of ultra-fine equiaxed grains. Firstly, the oscillating laser beam causes the periodical fluctuation of molten metal in the molten pool, which promotes adequate diffusion of Zr elements during welding. Secondly, the homogeneous Zr element scattering in the molten pool has sufficient cooling conditions to precipitate the L1 2 -Al 3 Zr phase in all-weld metal. The cooling rate during solidification is less than the critical temperature calculated by the time-dependent nucleation theory, which creates favorable conditions for forming primary Al 3 Zr. Finally, dense efficient nucleation sites prompt the formation of ultra-fine grains in all-weld metal. Compared with the single laser welding joint, the grain size decreases from 106.7 to 7.7 μm, and the tensile strength increases from 228 to 379 MPa. The microhardness of the fusion zone is equivalent to that of heat affected zone. These findings suggest that further improvements in mechanical properties cannot achieved by improving the process of fusion welding. [ABSTRACT FROM AUTHOR]

• Used deep penetration tungsten inert gas welding to make mid-thick plate T-joints. • Thoroughly studied the microstructure and mechanical properties of the T-joint. • The distribution of brittle B G is a fundamental influence on crack propagation. The deep penetration tungsten inert gas welding process was first used to realize efficient manufacturing of T-joints. The macroscopic morphology, microstructure, microhardness, and mechanical properties of T-joints were investigated. The welding parameters are a welding current of 465 A, a welding speed of 4 mm/s, and the distance between the tungsten electrode tip and the web plate and flange plate is 2 mm. The one-side welding both sides formation of T-joint was realized under these welding parameters. The Widmanstätten austenite in the web plate's overheated zone hinders the crack's propagation. The failure crack in the flange plate first propagates in the brittle fusion zone and then propagates in the weld metal. The fracture mode of DP-TIG joints of Q345 steel is mainly brittle fracture. The maximum tensile strength of the joint welded using DP-TIG is 302.15 MPa. [ABSTRACT FROM AUTHOR]

Weld cracks and low weld strength of Nb521 to GH3128 dissimilar metal welded joint are key factors influencing their weldability. To obtain favorable crack-free laser welded joints, this research adopted copper as an interlayer to research the microstructure and properties of laser direct welded and laser offset welded joints of Nb521 to GH3128 superalloy. Compared to previous research results, the tensile strength of laser direct welded joints is enhanced by 2.5 folds. There is a melting reaction layer at the position where the center welded joints are adjacent to the Nb521 base metal, and Ni 3 Nb and Laves phases are present in the layer. The copper solid solution is located in the center of fusion zone, and Ni 3 Nb-Laves hard particles are found. The phases near the side of GH3128 superalloy base metal are Ni solid solution, Cu solid solution, Ni 3 Nb/Cr 2 Nb hard particles and high melting point alloy mixture. Macrosegregation at the laser offset welding fusion zone is more serious. The phases near the Nb521 base metal are Nb solid solution, Cu solid solution, Ni 3 Nb and Cu/Cr eutectic structure. At the center of the fusion zone, Cu solid solution, Ni 3 Nb and Cu/Cr eutectic structure are observed. The phases near GH3128 base metal are Ni solid solution, Cr 2 Nb phase and Cu solid solution. Mean Vickers hardness values of the direct welded fusion zone is 271.7 ± 129.8 HV, which reduces mismatching of hardness of the joints to a certain degree. As there are Laves phase and Ni 3 Nb brittle phase in the melting reaction layer adjacent to Nb521 base metal, the microhardness value is up to 589.1 HV. The average microhardness of the offset welded fusion zone is 449.1 ± 217.4 HV, which is higher than the hardness of Nb521 and GH3128 base metals, due to increasing number of brittle phases in the joints. Strength values of the direct welded and offset welded joints are 418.7 ± 49.8 MPa and 364.3 ± 24.5 MPa respectively, which are separately 86.0% and 74.8% of Nb521 base metal. Fractures are all found to occur at the fusion zone on the side of Nb521. The direct welded joints exhibit mixed fracture characteristics with dimples and cleavage facets on the fracture, while the offset welded joints are characterized by brittle fracture. • Crack-free joints with excellent performance of Nb521 to GH3128 superalloy was achieved by using copper as an interlayer. • The strength of laser welded joints can reach up to 418.7 ± 49.8 MPa, which is 2.5 times of the previous result. • The effect of laser offset on the microstructure and mechanical properties of laser welded joints was investigated. [ABSTRACT FROM AUTHOR]

The thermal effects of the "keyhole" full penetration welding mode, which is characteristic of high-power CO2 laser, are simulated introducing a multipoint-line thermal source model based on heat conduction, parameterized by the distribution of the laser beam power, and the setting of the source system layout, and to be fitted on experimentally detected cross sections of the heat-affected or fusion zones of the weld. The proposed model allows to express the thermal field according to the moving reference system fixed on the overall heat source, and to analyze the temperature profiles that develop in some detection points fixed on the workpiece, as time varies during the welding process. By this way, it can be useful in evaluating the thermal effects that result from the variation of the main welding parameters (beam power, welding speed, plate thickness), with the aim of simplifying the selection of the optimal process conditions. As an application, reference is made to a cross section of a joint between plates of AISI 304 L austenitic steel. The fitting procedure allows to set the power distribution and layout parameters of the most suitable source combination (obtained by superposition of a line and two point sources). The value of the absorption coefficient also is assumed as fitting variable, so to overcome the complex problem of evaluating the beam power actually absorbed by the material on keyhole mode welding. Finally, the fitted model is applied to carry out a detailed thermal field analysis in the welded plates. [ABSTRACT FROM AUTHOR]

Resistance projection welding is a non-polluting mechanized process used to obtain an assembly between similar or dissimilar metallic materials. The main advantages of this welding process are the possibility to achieve many different welded points at the same time and the long life of the electrodes compared to the spot-welding process. The paper analyses the effects of thin aluminium coating existing on mild steel parts of on the correct formation of welding points when assembling moulds for the manufacture of baking bread. From optical and electron microscopy analyses it resulted that some adjacent welded points show an interrupted fusion line, sprinkled with elongated islands of aluminium-rich compounds. The paper presents the effect of changing the values of the welding parameters on the weld spot size, in correlation with the Al-rich inclusions that appear on the weld fusion zone. The best results have been obtained when the welding parameters values were the follows: electrode pressure of 2.6 bar, welding power of 19.18kVA and welding time of 7ms. The problems that occur when electric resistance welding of parts with aluminium coating have been highlighted, being useful for specialists who make products using this welding process. [ABSTRACT FROM AUTHOR]