Welding Research Articles

Fracture toughness and microstructural analysis of rotary friction welded S355J2 and SS316L steels for critical applications

Dissimilar metal welding is seeing growing adoption across industries to enhance structural functionality and efficiency. Achieving high-quality, defect-free dissimilar weld joints requires a comprehensive understanding of the interrelationships between the welding-induced microstructural changes and the material's performance characteristics, particularly its fracture-related properties. This study investigates the impact of microstructural changes on the fracture toughness of dissimilar welds between structural low-carbon steel (S355J2) and austenitic stainless steel (SS316L) prepared using the Rotary Friction Welding (RFW) technique. Welding preforms were created from respective pipe pup pieces. The evaluation involves microstructural analysis, tensile testing, hardness testing, and fracture toughness testing using compact tension specimens derived from various zones of the weld joints. Results revealed significant microstructural differences across the weld joint. The weld region exhibited stable hardness with a maximum of 208 HV1 in S355J2′s thermo-mechanically affected zone (TMAZ). High tensile strength (Ultimate Tensile Strength 540 MPa, Yield Strength 367 MPa) with failures mainly on the S355J2 side. The fracture toughness (KQ) matched parent metal values, with the RFW weld centre line (WCL) showing superior crack tip opening displacement (CTOD) of 0.35 mm. Fractography generally indicates ductile failure.

Evolution of Precipitates in a Mechanical Vibration-Assisted Metal Inert Gas Welded Joint of 6082-T6 Aluminum Alloy Made with an ER5356 Filler Wire

Evolution of Precipitates in a Mechanical Vibration-Assisted Metal Inert Gas Welded Joint of 6082-T6 Aluminum Alloy Made with an ER5356 Filler Wire

Crucial effects of plasma gas on the weld and microstructural characteristics of plasma arc welded aero engine Ti6Al4V alloy joints

This study explores the influence of plasma gas flow rate (PGFR) on the defects, microstructure evolution and mechanical properties during plasma arc welding of Ti6Al4V titanium alloy thin sheets using microscopic analysis, spectroscopic analysis, tensile and microhardness tests. The variation in PGFR affects the welding arc in terms of its stability, pressure and constriction which results in transformation of arc from conduction mode to keyhole mode and changes in microstructure as well. All the other welding process parameters were kept constant except for PGFR which was varied to investigate its significance. Excess weld metal was observed under the weld bead is an attribute of keyhole formation. Macrographs exhibits increments in weld geometry measurements whereas weld defects such as lack of penetration and porosity decreased with increased PGFR. The microstructural examination showed a variety of phase formations that includes majorly with acicular α and Widmanstätten α morphologies. Tensile strength and hardness at the weld region of the welded joints increases with increase in PGFR. An oxygen rich brittle subsurface layer called α-case morphology was observed at the weld region of 1 L/min joint causes significant reduction in ductility.

A modified physics-informed neural network to fatigue life prediction of deck-rib double-side welded joints

Deck-rib welded joint is an important part of orthotropic steel decks, which are susceptible to fatigue cracks under various load cycles. Therefore, it is essential to use efficient predicting methods to assess the fatigue performance of deck-rib welded joints with new geometry and form in order to ensure a reliable operation of the bridge. A modified physics-informed neural network (PINN) is proposed for the fatigue life prediction of the novel deck-rib double-side welded joints. The modified PINN incorporates implicit physical model as an activation function into the hidden neurons, and explicit physical constraints into the loss function. Additionally, the influence of deck thickness is integrated using limited test sample data based on the observational approach. The 62 experimental data were taken from the literature to compare the performance of the artificial neural network (ANN), traditional PINN and the modified PINN. The results demonstrate that the modified PINN enhances the learning process of the neural network through the joint learning of physical knowledge by activation function and loss function. Furthermore, the fatigue life prediction of the deck-rib double-side welded joints under the modified PINN exhibits physical consistency and accuracy when compared with the traditional ANN and PINN.

Experimental and numerical investigations on dynamic response of butt-welded plates subjected to blast load

Experimental and numerical investigations on the small-size butt-welded plates subjected to air blast loads were conducted to highlight the effect of welded joints on the blast proof structures. The inherent characteristics of welded joints, including geometry, mechanical properties and welding residual stress were evaluated and discussed in the computation of blast loading. The geometry shape was assessed through macrographic of the welded joints. The distribution of mechanical and thermal physics property was determined through basic experiments using the specimens extracted from different zones of a welded joint. Welding residual stress was calculated in a thermo-mechanical coupled model. Conventional Weapons Effects Program (CONWEP) is more economic but limited compared with Arbitrary-Lagrangian–Eulerian (ALE) method. ALE and CONWEP methods were applied to simulate the air blast load applied on the plates. Effectiveness and efficiency of the methods were discussed. The results of the two programs could both coincide well with the experiment measurements. The models under six conditions were calculated to uncouple and discuss the effect of material property distribution and welding residual stress on the dynamic response of the welded structure. Permanent deflections were considered to assess the capacity of welded structures. Welding residual stress fields and the local weak materials are advantageous to the bending deformation. The phenomenological expressions of permanent deflection across thickness under different welding conditions were established based on simulation results. The effect of aspect ratio of the welded structures was also be discussed.

The formation mechanism of void in thin-walled capsule welding joint induced by HIP

Thin-walled capsule significantly impacts the overall quality of hot isostatic pressing (HIP）products, with capsule reliability being a crucial factor in determining the success or failure of the HIP process. High-temperature creep is essential for the densification of HIP powder. However, the capsule, made of dense metal, undergoes its own creep process. High temperature and high pressure may induce void formation in the capsule due to diffusion and creep. The integrity of the capsule typically relies on the welding process, and void formation at welded joints poses a significant challenge to the capsule’s reliability, increasing the likelihood of failure. This study investigates the mechanisms of void formation in welded joints during the HIP process. Results indicate that high temperature and high pressure during HIP promote the formation of two types of voids in mild steel: Kirkendall voids and creep voids. Kirkendall voids are driven by diffusion and influenced by the HIP insulation temperature, which affects their state but not their formation. Creep voids, however, originate from stress concentration at grain boundaries during creep deformation. Their distribution density is positively correlated with the degree of creep deformation, which is primarily controlled by HIP pressure and temperature.

Effect of TIG remelting on the microstructure, mechanical properties, and corrosion behavior of 5052 aluminum alloy joints in MIG welding

In this work, the effect of tungsten inert gas (TIG) remelting on the microstructure, mechanical properties, and corrosion resistance of 5052 aluminum alloy joints produced by metal inert gas (MIG) welding is investigated. The results indicate that after TIG remelting of MIG welds, the proportion of dendrites increases in the remelted weld zone (WZ), porosity decreases by 76.9%, and the Fe elements in the second phase become coarser and more segregated. In contrast, the Mg elements form a solid solution with a decreased degree of segregation. In addition, the average grain size of the remelted structure decreases, while the proportion of sub-grain boundaries (SGBs) and the kernel average misorientation (KAM) values increase. Moreover, the heat-affected zone (HAZ) widens, and the grains become coarser. An increase of 4.5% in tensile strength and 20.0% in elongation was observed in the TIG-remelted joints after TIG remelting. Electrochemical and immersion tests on the TIG-remelted microstructure showed reduced corrosion resistance. Electrochemical tests mainly exhibited galvanic corrosion, resulting in the formation of pits. The types of corrosions observed in the immersion test differ from those in the electrochemical test, primarily exhibiting exfoliation corrosion and pitting corrosion. A higher geometric dislocation density (ρGND) in the structure increases the susceptibility to corrosion.

The influence of anodization on laser transmission welding between high borosilicate glass and TC4 titanium alloy

This study investigates the influence of the thickness of the oxide film formed on the surface of TC4 titanium alloy after anodization on the laser transmission welding between the titanium alloy and high borosilicate glass. The effects of oxidation time on the morphology and thickness of the oxide film were examined, and the elemental and phase composition of the oxide film were characterized. The differences in welding strength, weld morphology, and fracture surface between the titanium alloy before and after oxidation treatment and high borosilicate glass welding were compared, and analyzed the welding seam formation mechanism. Within our research scope, the results indicate that with an increase in oxide film thickness, the surface roughness gradually increases and the internal voids gradually increase, resulting in a decrease trend in the bonding strength of the welded joints with the increase in oxide film thickness. The interpenetrating structure formed by the mutual infiltration of glass and metal in the molten pool is identified as the main reason for their connection.

The influence of various welding wires on microstructure, and mechanical characteristics of AA7075 Al-alloy welded by TIG process

Owing to their exceptional mechanical properties, the various welding wires used to combine aluminum can meet the needs of many engineering applications that call for components with both good mechanical and lightweight capabilities. This study aims to produce high-quality welds made of AA7075 aluminum alloy using the GTAW technique and various welding wires, such as ER5356, ER4043, and ER4047. The microstructure, macrohardness, and other mechanical characteristics, such as tensile strength and impact toughness, were analyzed experimentally. To check the fracture surface of the AA7075 welded joints, the specimens were examined using optical and scanning electron microscopy (SEM). A close examination of the samples that were welded with ER5356 welding wire revealed a fine grain in the weld zone (WZ). In addition, the WZ of the ER4043 and ER4047 welded samples had a coarse grain structure. Because the hardness values of the welded samples were lower in the WZ than in the base metal (BM) and heat-affected zone (HAZ), the joints filled with ER5356 welding wire provided the highest hardness values compared to other filler metals. Additionally, the ER4047 filler metal yielded the lowest hardness in the weld zone. The welding wire of ER5356 produced the greatest results for ultimate tensile stress, yield stress, welding efficiency, and strain-hardening capacity (Hc), whereas the filler metal of ER4043 produced the highest percentage of elongation. In addition, the ER4047 fracture surface morphology revealed coarser and deeper dimples than the ER5356 fine dimples in the welded joints. Finally, the highest impact toughness was obtained at joints filled with the ER4047 filler metal, whereas the lowest impact toughness was obtained at the BM.

Selective adsorption and corrosion mechanism of SO2 and its hydrates on X65 welded joints steel in CO2-saturated aqueous solution

In this study, the corrosion mechanism in different regions of the welded joints in CO2/SO2 saturated aqueous solution was investigated by electrochemistry and morphological analysis. The results demonstrated that SO2 and its hydrolysis have some adsorption properties and tend to adsorb in the region of the base metal and generated FeS product. A dense corrosion product film could form on this region, effectively reducing the corrosion rate. Due to the selective adsorption which increases the potential difference between different regions of the welded joint, further intensifying the galvanic corrosion and ultimately leading to the failure of the welded joint.

Microstructure and fatigue properties of laser-MIG hybrid welding of medium-thickness 6005A aluminum alloy

Light alloys represented by aluminum alloys have a wide range of applications in railway transportation, the key load-bearing parts of high-speed train bodies are welded with a large number of medium-thickness plates, so the study of the welding performance of medium-thickness aluminum alloy plates is significant. In this study, laser-MIG hybrid welding technology is used to realize the single-layer, single-pass welding of 6005A aluminum alloy plate with a thickness of 10 mm. The grains in the weld zone (WZ) are coarsened by welding heat, and the average diameter is about 1.6 times that of the base metal (BM), while the average grain diameter in the heat-affected zone (HAZ) is similar to that of the BM. A softening phenomenon is observed in the welded joint, with a minimum hardness of 72.6 HV in the HAZ. TEM analysis shows that the softening phenomenon is caused by the coarsening of precipitate phases in the HAZ. In terms of tensile properties, the ultimate tensile strength (UTS) of the welded joint is approximately 237 MPa, which is 70.1 % of the BM. The fatigue strength (Nf = 2 × 106 cycles) of the welded joints is predicted to be 83 MPa, which is 64 % of the yield strength (YS), from the S-N curve obtained by fitting the tension–compression fatigue test data. Different morphologies of secondary phase particles are observed in the fatigue crack propagation zone, and their formation and effects on secondary crack are described. The fracture location indicates that softening behavior in the HAZ is the main factor influencing tensile performance, while defects in the WZ are the primary factors affecting fatigue fracture. The experimental results can enrich the tensile and compressive fatigue data of 6005A aluminum alloy.

Optimization investigation of parameters for spot-welding of AA2014 and AISI316 dissimilar alloys

The objective of the research was to determine the exact process parameters required for spot-welding AA2014 and AISI316 alloys. The main focus was on achieving particular welding results, including nugget diameter, hardness, and tensile shear fracture load (TSFL). The central composite rotatable design model within the framework of a Response Surface Methodology (RSM) optimization approach, the study sought to intensify key spot weld process factors. The mechanical characteristics and nugget diameter of the welded joints were analyzed by carefully examining these factors to determine their significant effects. The investigation yielded crucial insights, revealing that the highest strength of welded joints, characterized by a nugget diameter of 5.982 mm, hardness of 149.6 VHN, and TSFL of 2.355 KN, was achieved at 3.4 kgf, when accompanied by 60 W power and a 2.5s duration. Notably, power emerged as the predominant factor driving the spot-welding process. Furthermore, microhardness and TSFL displayed direct correlations with power, while nugget diameter exhibited an inverse relationship. Moreover, rigorous statistical analyses, including F-tests and ANOVA, provided robust validation, indicating that the observed values fell comfortably within a 99.5% confidence interval for hardness, nugget diameter, and TSFL. These meticulously derived conclusions represent a significant stride towards establishing more standardized and efficient spot-welding protocols, particularly beneficial for the manufacturing sectors dealing with mild steel and aluminium materials.

Effect of Different Welding Speeds on Microstructure and Properties of Bobbin Tool Friction Stir Welded Joints of T2 Pure Copper

Effect of Different Welding Speeds on Microstructure and Properties of Bobbin Tool Friction Stir Welded Joints of T2 Pure Copper

Effect of temperature compensation on properties and interfacial structure evolution of Al/CFRTP ultrasonic welded joints

Effect of temperature compensation on properties and interfacial structure evolution of Al/CFRTP ultrasonic welded joints

Gap bridging in laser welding of EN AW 5083 with different joint configurations via beam oscillation and filler wire

The extended use of laser welding in the industry requires a less sensitive process in terms of geometrical tolerances of the joint edges. As the industrial availability of laser systems increases, the demand to use laser welding technology possibly with parts coming from less precise production steps is increasing. Gap formation is often caused by the edge quality of the parts coming from previous manufacturing steps such as sheet forming. Al alloy sheets deformed to box-shaped 3D forms often require welded joints on the edges in lap, but, and corner joint configurations. These joints are hard to carry out by laser welding due to the large gap formation caused by the tolerances of the deformation processes involved. Laser welding of Al alloys is already challenging in the absence of gap formation, while these joint configurations have been not feasible with a stationary beam due to incomplete fusion and defect formation. Laser welding with beam oscillation and wire feeding can improve the weldability of these joints. The oscillating motion of the high-intensity beam can achieve a deep weld together with a wider seam. Combined with wire feeding, the process can close gaps in the butt, lap, and corner joint configurations. On the other hand, the added oscillation and wire-related parameters require extending the experimental space, which requires a methodological study to identify feasible conditions. Accordingly, this work proposes a methodological approach to identify and set laser welding process parameters with beam oscillation and wire feeding for an EN AW 5083. Process parameters were initially studied using a simple analytical model that depicts the beam trajectory. Bead-on-plate tests were conducted to assess beam size, power, and weld speed ranges. Lap, butt, and corner joint conditions with a 0.5-mm gap were welded with high quality by manipulating the laser power, oscillation amplitude, and wire feed rate. The results show that welding speeds could be maintained as high as 55 mm/s with complete filling of gaps of up to 0.5 mm, eliminating the surface undercuts and achieving weld widths in the order of 2.5 mm. Moreover the results show the possibility control the depth of the welds from 3 mm to full-penetration conditions.

Time-domain fatigue reliability analysis for floating offshore wind turbine substructures using coupled nonlinear aero-hydro-servo-elastic simulations

The present study aims to develop a novel methodology for the fatigue reliability analysis and design for a floating offshore wind turbine substructure using its fully coupled nonlinear dynamic responses in the time domain. The developed methodology offers a computationally efficient yet robust assessment for designing fatigue-critical welded joints on floating substructures. The methodology starts with the sea state selection based on the fatigue damage contribution of all the sea states in the scatter diagram. To this end, the dynamic response is analysed by fully coupled aero-hydro-servo-elastic simulations using OpenFAST. The resulting short-term fatigue loading is then used to estimate the hotspot stress history using the analytical solution for global structural analysis and the empirical solution for the stress concentration factor. The long-term fatigue damage is calculated as the joint probability-weighted sum of the short-term fatigue damage using Palmgren-Miner's linear damage rule. Afterwards, the selected sea states are used to perform dynamic response simulations with multiple random seeds, ensuring no significant accuracy loss. To obtain the probabilistic fatigue life prediction, a novel time-domain fatigue reliability analysis algorithm is developed based on the bootstrapping method, which creates a pool of short-term fatigue responses with different random seeds and combines them within a Monte Carlo Simulation. Finally, the fatigue reliability analysis considering the S-N and damage-tolerant approaches for design is carried out.

Interfacial microstructure and mechanical property of dissimilar resistance spot welded joint of TC4 titanium alloy and 316L stainless steel with nickel interlayer

Dissimilar materials of TC4 titanium alloy and 316L stainless steel were joined by means of resistance spot welding with nickel interlayer in different thicknesses. A significant enhancement in terms of nugget morphology quality with less defects was achieved for the welded joints with nickel interlayer compared with that without interlayer. With increasing the nickel interlayer thickness from 50 μm to 300 μm, the effective nugget diameter increased gradually from ∼4.8 mm to ∼5.2 mm, which was lower than that of the interlayer-free welded joint being ∼5.9 mm. A thinner intermetallic compound layer with dual-layered structure features with thickness of ∼11 μm was formed at the nugget/titanium interface in the welded joint with nickel interlayer compared with that of the interlayer-free welded joint, meanwhile an intermetallic compound layer with thickness of ∼3 μm was formed at the nugget/stainless steel interface, which exhibited serrated structure features. The introduction of nickel interlayer in the welded joint could suppress the formation of the brittle Ti–Fe intermetallics such as Fe2Ti, and facilitate the formation of TiNi, Ti2Ni and TiNi3. A more homogeneous current density distribution and a lower peak temperature (1809 °C) during welding were achieved via employing nickel interlayer. With increasing nickel interlayer thickness from 0 μm to 300 μm, the tensile shear load of welded joints experienced an increased tendency first and then decreased, meanwhile the maximum tensile shear load of 3.7 kN was obtained with the interlayer thickness of 200 μm, which was 61% higher than that of the interlayer-free welded joint.

The influences of nanoparticles on the microstructure evolution mechanism and mechanical properties of laser welded stainless steel/aluminum

In order to solve the problem of poor performance of welded joints of steel and aluminum dissimilar materials, this study proposes the use of ceramic particle-reinforced aluminum alloy as an alternative to traditional aluminum alloy for welding, effectively overcoming this problem. In this paper, the laser welding of stainless steel/6061 aluminum alloy (SA) and stainless steel/TiC–TiB2 duplex nanoparticle-reinforced 6061 aluminum alloy (SRA) was realized. The effect of ceramic nanoparticles on the microstructure and mechanical properties of SRA joint was systematically studied, and the strengthening mechanism of nanoparticles was revealed. Under the same process parameters, the melting zone of SRA joint is larger and the intermetallic compound (IMCs) layer is narrower. Moreover, the grain size of the brittle Fe–Al compound phase in the IMCs layer is significantly reduced, which effectively inhibits the initiation of cracks at the steel/aluminum interface. The study shows that ceramic particles have a pinning effect on the dislocations, limiting the grain growth, reducing the thickness of the intermetallic compound layer, and decreasing the content of the brittle FeAl3 phase. Moreover, ceramic nanoparticles promote the formation of Mg2Si strengthened phase at the grain boundary, further hinder the dislocation movement and improve the strength of the joint. Under the welding power of 3400 W and welding speed of 31 mm/s, SRA joint achieves the maximum tensile shear of 1718 N, which is 15% higher than the strength of SA joint.

Strength and Fracture Toughness of TIG- and Laser-Welded Joints of Low Carbon Ferritic Steels.

This paper presents the results of experimental testing of joints welded using conventional TIG and laser methods. The welded components were sheets of the low-carbon steels 13CrMo4-5 and 16Mo3. Welded joints were made using different levels of linear welding energy. In the case of laser welding, a bifocal beam with longitudinal positioning of the focal lengths in relation to the welding direction was used. Experimental tests on welded joints included a bending test and determination of hardness distribution, mechanical properties, and fracture toughness, as well as microstructural research in the material of the various joint zones. Based on the determined strength characteristics, the true stress-strain relationships were defined, and a numerical model of the laser joints was developed in Abaqus 6.12-3. The modelled joint was subjected to loading to determine the most stressed areas of the joints. The numerical results were compared with those obtained using GOM's Aramis 3D 5M digital image correlation system. The system used made it possible to record displacements on the surface of the analysed joints in real time. Good agreement was obtained between the strain fields calculated numerically and those recorded using the Aramis 3D 5M video system. The numerical calculations provided information on the strains and stresses occurring inside the analysed joint during loading. It was found that the welded joints were characterised by increased hardness and high strength properties in relation to the base material. The bending test of the laser-welded joints gave a positive result-no cracks were observed on the face or root of the weld. The fracture toughness of the joint zones is slightly lower in relation to that of the base material, but no brittle fracture was observed.

Magnetic controlled arc welding technology: a review

PurposeThe purpose of this study is to optimize and improve conventional welding using EMF assisted technology. Current industrial production has put forward higher requirements for welding technology, so the optimization and improvement of traditional welding methods become urgent needs.Design/methodology/approachExternal magnetic field assisted welding is an emerging technology in recent years, acting in a non-contact manner on the welding. The action of electromagnetic forces on the arc plasma leads to significant changes in the arc behavior, which affects the droplet transfer and molten pool formation and ultimately improve the weld seam formation and joint quality.FindingsIn this paper, different types of external magnetic fields are analyzed and summarized, which mainly include external transverse magnetic field, external longitudinal magnetic field and external cusp magnetic field. The research progress of welding behavior under the effect of external magnetic field is described, including the effect of external magnetic field on arc morphology, droplet transfer and weld seam formation law.Originality/valueHowever, due to the extremely complex physical processes under the action of the external magnetic field, the mechanism of physical fields such as heat, force and electromagnetism in the welding has not been thoroughly analyzed, in-depth theoretical and numerical studies become urgent.