• Effects of global tensile residual stresses on the fatigue of welded joints. • Numerical welding simulations revealed differences under varied boundary conditions. • Experimental fatigue tests on welded joints under elevated mean stress conditions. • Successful inclusion of welding boundary conditions in fatigue assessment. Large-scale engineering as-welded structures typically generate high tensile residual stresses due to the structural stiffness restricting the contraction of weldments. These tensile residual stresses can often reach the yield strength of parent material. In small-scale specimens, similarly high tensile residual stresses locally at the weld toes can be achieved by appropriately selecting the joint type and using sufficiently large dimensions. However, it is not yet known whether different primary (global) and tertiary residual stress components significantly influence the local fatigue strength of welded specimens, or whether they should be considered in fatigue assessments. The objective of the current work is to experimentally and numerically investigate the residual stresses and fatigue strength of welded-around longitudinal gusset joints made of high-strength 690QT ship steel under various mean stress conditions, representing different boundary constraints in welded structures. First, welding deformations and residual stresses are numerically estimated using an experimentally validated heat source model and sequentially coupled finite element model. Herein, different boundary conditions are applied to study the evolution of local residual stresses and their components at the fatigue-critical weld. Secondly, fatigue tests are experimentally performed on similarly welded longitudinal gusset joints under different mean stress conditions that reflect the simulated residual stress fields. The numerical simulation results reveal clear differences in residual stress gradients and components across the different boundary conditions. Differences in the improvement factors between the constant minimum stress test series with respect to the constant mean stress condition were found to be 1.52 (no elevation) and 1.31 (elevated global mean stress). The findings of this work highlight the importance of considering boundary conditions in the evolution of welding-induced residual stresses, as well as their inclusion in fatigue assessments.

A comprehensive review on the effect of TIG welding parameters on intermetallic formation and mechanical properties of dissimilar aluminum alloy welds

Study on the strengthening mechanism of nitrogen–titanium combination alloying for laser beam welding joint of molybdenum alloy

• Ni-1 intermediate buffer layer effectively restricted carbon migration, , which led to resistance against the formation of CDZ and CEZ • Ni-1 buffer with PWHT enhanced P91 HAZ impact toughness by 14%. • GTAW with Ni-1/IN625 provided enhanced P91–304 L weld performance. • The Ni-1 buffer resulted in homogeneous delta ferrite distribution. • Highest hardness was in CGHAZ and lowest in ICHAZ across all joints. The pursuit of efficiency in nuclear power plant components operating at high steam temperatures and pressures has driven the use of advanced alloys like P91 steel and 304 L stainless steel, yet the structural integrity of their dissimilar welds remains challenged by carbon migration and premature failure; prompting this study to investigate the effectiveness of a Ni-1 (∼92% Ni) intermediate buffer layer combined with ERNiCrMo-3 (IN625) filler metal via multi-pass Gas Tungsten Arc Welding to enhance their metallurgical and mechanical performance. The study compared three IN625 buttering applications: as-welded, post-weld heat-treated, and post-weld heat-treated with an intermediate Ni-1 buffer layer. Microstructural analysis, employing optical microscopy and scanning electron microscopy, revealed peninsula features and an unmixed zone at the interface. The fusion zone features included Mo, Nb, and Ti-rich precipitates. The P91 heat-affected zone demonstrated a soft delta ferrite zone. Mechanical testing showed tensile strengths of 674 MPa (as-welded), 653 MPa (post-weld heat-treated), and 633 MPa (post-weld heat-treated with buffering). Notably, the Ni-1 buffer with post-weld heat treatment resulted in a 14% improvement in P91 heat-affected zone impact toughness compared to the as-welded joint. Microhardness profiling revealed the highest hardness in the coarse-grain heat-affected zone and the lowest in the intercritical heat-affected zone. The study concludes that the Ni-1 buffer layer successfully suppresses carbon migration, preventing the formation of detrimental carbon-depleted and enriched zones. By mitigating metallurgical degradation and improving toughness, the Ni-1/IN625 dual-filler approach provides a robust solution for the structural reliability of P91-304 L SS joints in demanding nuclear applications.

Study on corrosion fatigue performance of aluminum alloy high power laser filled wire welding joints

This paper describes a study on the formation and process parameters of friction stir welding joints on 6 mm thick copper plates. Numerous experiments were conducted at lower rotational speeds and moderate welding traverse speeds to obtain optimal process parameters for high-quality friction stir welding joints with good surface formation and no internal defects. Simultaneously, considering the thickness tolerance fluctuations in the large-scale engineering application of Copper FSW, tests were conducted with pin lengths and shoulder plunge depths less than the plate thickness. Additionally, a unique modular stirring tool was designed by ourselves to reduce costs in large-scale engineering applications. The experimental results demonstrate that under the parameters of a rotational speed of 275 r min−1 and a traverse speed of 120 mm min−1, welding joints with both surface and internal integrity can be achieved, with the joint strength level exceeding 80% of the base material. The mechanical weak point of the joint is located in the TMAZ region just below the pin as revealed by SEM testing, which shows both plastic and brittle fractures. EDS results indicate no inclusions or second-phase precipitates at the surface and port locations.

This study investigates the performance of Flux-Bounded Tungsten Inert Gas (FB-TIG) welding using TiO2 flux for butt welding of SS304L stainless steel plates. The primary objective was to evaluate weld penetration, bead geometry, microstructural evolution, and tensile properties of the welded joints. Experimental trials established optimised parameters at 170 A welding current, producing full penetration without undercut formation. Macrostructural analysis revealed deep, narrow fusion zones with high depth-to-width ratios, while microstructural examination confirmed refined dendritic growth, stable δ-ferrite distribution, and a narrow heat-affected zone. The fusion line exhibited clean epitaxial solidification and defect-free bonding. Mechanical testing demonstrated that FB-TIG welded joints retained over 93% of the base metal’s ultimate tensile strength and more than 50% ductility, validating the robustness of the process. These findings highlight FB-TIG welding with TiO2 flux as a reliable, industrially viable technique for producing high-quality stainless-steel joints in critical applications such as pressure vessels, chemical processing, and energy systems.

Friction Stir Weld (FSW) joints of precipitation hardened Al-Cu binary alloy (AA2219-T87) thick plates often exhibit low strength owing to coarsening and dissolution of precipitates (Al2Cu) during the process. The present work aims to increase the traverse speed using hybrid tool-pins (HTPs: a combination of triangular and threaded conical pin surfaces) for 10 mm thick plates, and to compare the weld quality parameters (size of the weld zones and peak temperatures in the weld zones) with that of conventional threaded conical tool-pin (TCTP). An Arbitrary-Lagrangian-Eulerian (ALE) model was developed for thermal-material flow-structural mechanics phenomena, and the FSW process was simulated using TCTP and HTPs to determine the most suitable tool-pin profile First, the accuracy of the ALE model in predicting the size of the weld zones using the TCTP at a traverse speed (TS) of 200 mm/min and rotational speed (RS) of 500 rpm was validated against experimental data, showing close agreement with a relative error of less than 10%. Second, the ALE model predicted results with HTPs at TS of 600 mm/min and RS of 1000 rpm demonstrating lower peak temperatures and narrow weld zones in contrast with TCTP, which are attributed to enhanced mixing of shoulder and pin surface driven material flow regions around the rotating tool.

The present experimental investigation is to enhance the flexural strength of aluminium matrix composites (AMCs) manufactured with AA7075 reinforced with different weight percentages (3%, 5%, 7% and 9%) of silicon carbide (SiC) particles by optimizing friction stir welding (FSW) parameters. Both hexagonal and threaded hexagonal tool profiles were employed to weld the composites after they were manufactured using the stir casting. The FSW process parameters were varied based on a Taguchi L16 orthogonal array i.e. traverse speed, tool rotational speed, axial force and reinforcement percentage. The mechanical performance was assessed utilizing flexural testing. Tool traverse speed and rotational speed had a substantial effect on flexural strength for both tool types according to Analysis of Variance (ANOVA). At 5% SiC, 1500 rpm, 50 mm/min, and 850 N, the threaded hexagonal tool outperformed the hexagonal tool with maximum flexural strength of 384.90 MPa. Scanning electron microscope (SEM) analysis indicates that the use of a threaded hexagonal tool with 5% SiC reinforcement improves material flow and particle distribution resulting in decreased defects and enhanced mechanical performance of the weld joint. The excellent correlation between the predicted and experimental findings was confirmed by regression models developed for both tool geometries. These results confirm that AA7075/SiC composites can be used for high-performance structural applications.

This study investigates the impact of titanium dioxide (TiO2) nanoparticles on the thermomechanical behavior of L-shaped welded joints in steel structures. Nanoparticles were incorporated into the weld metal at three weight ratios (0.5, 1.25, and 2 wt%) using the cold spray coating technique, and the samples were heat-treated across a wide temperature range (25-900°C). Experimental results demonstrated that the addition of 2 wt% TiO2 nanoparticles significantly enhanced the ultimate load capacity by up to 25% compared to nanoparticle-free joints. The improvement was more pronounced in thicker steel sheets (30mm), where uniform nanoparticle distribution and better stress dissipation were observed. The resistance recovery coefficient decreased from 94 to 97% at lower temperatures (25-400°C) to 60-80% at 900°C, with nanoparticle-enhanced samples showing superior retention of mechanical properties. Microstructural analysis confirmed the anatase phase of TiO2 with an average crystallite size of 20nm and spherical morphology (20-40nm). Computational fluid dynamics (CFD) simulations revealed that nanoparticle porosity and specific surface area critically influence heat transfer and pressure drop in coated welded joints, with optimal thermal performance achieved at higher specific surface areas. This work highlights the synergistic effects of TiO2 nanoparticles, sheet thickness, and thermal treatment on weld performance, offering a promising pathway for enhancing the durability and thermal management of steel structures in demanding applications.

Friction stir welding (FSW) is a solid-state welding process commonly used to join high-strength aluminium alloys due to its ability to produce high-quality welds with few defects and high mechanical performance. This research examined the effects of the main FSW process variables on the mechanical properties of AA2050 aluminium alloy joints through an integrated statistical and Machine learning framework. The key process variables were rotational speed, traverse speed, and axial load, which were optimized with the help of Response Surface Methodology based on the BBD consisting of fifteen experimental runs. Tensile tests and Vickers microhardness tests were conducted to evaluate the mechanical performance of the welded joints. ANOVA was used to assess the statistical significance of the derived regression equations, and the developed models exhibited coefficients of determination (R 2) of 0.8567 for tensile strength and 0.8267 for microhardness, indicating moderate-to-good agreement between experimental and predicted values. Multi-response optimization using the desirability function predicted an optimal parameter combination of 989.53 rpm rotational speed, 48.42 mm/min transverse speed, and 7.85 kN axial load, resulting in predicted responses of 298.67 MPa tensile strength and 150.25 HV micro hardness, with an overall desirability of 0.968. Furthermore, machine learning models were employed to validate and assess the predictive performance of the developed RSM models. The microstructural examination revealed significant grain refinement in the stir zone due to dynamic recrystallisation, resulting in a more homogeneous microstructure and improved mechanical performance. The results demonstrate that integrating RSM-based optimization with machine learning provides a reliable framework for optimizing FSW parameters and enhancing the performance of high-strength aluminium alloy welded joints.

ABSTRACT Heat exchangers used in underwater equipment are generally large and prone to failure due to welding defects and stress concentration at joint regions. In this study, the thermo-mechanical behavior of TC4/TA2 dissimilar titanium alloy tube-sheet welded joints was investigated using combined experimental and numerical methods, with emphasis on the welding temperature field, residual stress, and deformation. A residual stress scaling relationship among geometrically similar models of different sizes was established, and a predictive formula was proposed. The results show that the maximum residual stress reaches 722 MPa near the weld interface and varies nonlinearly with model size. The deformation is consistent with the stress distribution and is mainly characterized by inward shrinkage in the weld region. The proposed formula can be used for preliminary residual stress estimation and fatigue life prediction of large-scale tube-sheet welded joints based on small-scale welding simulations.

This paper investigates the interaction and propagation mechanisms of fatigue cracks in the welded joints of reusable launch vehicle propellant tanks, utilizing a combined FRANC3D/ABAQUS finite element simulation based on fracture mechanics. Three typical defect scenarios, that is, single crack, coplanar double cracks, and non-coplanar double cracks, were systematically modeled to evaluate the effects of loading parameters (stress ratio R ), crack geometry (inclination angle θ, size), and spatial arrangement. Results demonstrate that for a single crack, the stress ratio and inclination angle are the primary determinants of fatigue life. For coplanar cracks, both spacing and relative size critically influence propagation, with coalescence leading to severe life reduction; at a 1 mm spacing, the life of equal-sized double cracks is only 54% of a single crack’s. In non-coplanar configurations, reduced spacing induces a significant shielding effect on smaller cracks, and asymmetric propagation emerges upon loss of symmetry. The developed simulation framework provides a robust tool for damage tolerance assessment and establishes a fundamental theoretical basis for the structural optimization of welded aerospace structures .

Conventional fusion welding of aluminum pipes often leads to defects such as root cracking, thermal distortion, and lack of proper fusion. To address these issues, a dedicated friction stirs welding (FSW) setup along with a specially designed tool was developed for joining aluminum pipes. In this study, the influence of key process parameters, including tool rotational speed, traverse speed, and axial force, on weld quality and mechanical performance was investigated. The welded joints were evaluated using tensile testing, micro-Vickers hardness measurements, and visual inspection techniques. The results show that both tool design and process parameters play a significant role in determining weld quality. With properly selected parameters, improved mechanical properties and better weld integrity can be achieved.

This study investigates the optimization of selected process parameters in the rotary friction welding (RFW) process of CuSi3Fe2Zn3 silicon bronze alloys using Response Surface Methodology (RSM) with tensile strength as the primary response. The effects of rotation speed, friction time and friction pressure were evaluated, and the steepest ascent method was applied to determine the best parameters. The results indicated that rotation speed and friction time were the most influential parameters for enhancing tensile strength. A maximum tensile of 424 MPa was achieved under conditions of 3300 rpm, friction time of 25 s, friction pressure of 0.5 MPa, forging time of 16 s, and forging pressure of 8 MPa. However, confirmation experiments exhibited noticeable variability, indicating limitations in process repeatability. Tensile properties, hardness evaluation, microstructural characterization, and thermographic analysis were conducted to assess the quality of the welded joints. Microstructural analysis revealed recrystallized equiaxed grains in the welding center zone, consistent with severe plastic deformation, while microcracks and microvoids were observed and likely contributed for failure during tensile testing. Despite grain refinement, a reduction in microhardness was detected, suggesting the influence of thermal softening mechanisms. Thermographic analysis indicated that the average temperature at the welding center zone reached 564 °C. In conclusion, RSM proved to be a useful tool for identifying trends and guiding process optimization. The results highlight the importance of process stability and control in achieving consistent performance in RFW of copper-based alloys.

Suppressing the brittleness of Ti/Cu weld joint in TIG welding by alloying Fe in filler metal

Failure mechanism and quality evaluation in micro-resistance spot welds of braided Ag-plated Cu conductor to Cu interconnector

Rapid stress intensity factor evaluation in cracked welded joints

An equivalent structural stress method for variable-amplitude fatigue assessment of welded joints with load sequence effects

Improvement of microstructure and mechanical properties in U75V rail electroslag welding joints via temperature field control