Search Results (246)

To address issues of residual stress concentration and deformation in large-scale multi-seam laser welding of tube-to-tubesheet, we established a 12 mm thick Q235 steel simulation model. The model considers the material’s high-temperature performance and mechanical properties. We designed three welding paths: sequential welding, block-by-block symmetrical welding, and inward–outward symmetrical radial welding. The welding simulation software InteWeld 4.0 was used to study the effects of these paths on deformation. Results showed that the inside-out symmetric radiation welding path disperses heat input effectively. It prevents stiffness reduction from local heat accumulation. By using symmetrically distributed shrinkage forces that offset each other, this path greatly inhibits deformation accumulation. The maximum deformation was only 1.6 mm—5.9% and 33% lower than with block-by-block symmetric welding (1.7 mm) and sequential welding (2.4 mm). This path also resulted in a uniform residual stress distribution, with a maximum stress of only 250 MPa, making it the best option for suppressing deformation. Full article

Weld quality plays a critical role in ensuring the structural integrity and long-term performance of critical piping systems used across petrochemical, oil and gas, marine, and healthcare sectors. Although gas tungsten arc welding, shielded metal arc welding, and gas metal arc welding are widely applied in pipe fabrication, existing studies often examine these processes independently and provide limited insight into the comparative influence of process parameters on weld morphology, microstructure, and mechanical performance. This review consolidates findings from recent research to evaluate how welding current, arc voltage, heat input, travel speed, shielding gas composition, and joint preparation interact to affect weld bead geometry, heat-affected zone evolution, tensile properties, hardness, and overall weld integrity in piping systems. The primary objective of this review is to critically compare fusion welding process parameter optimization strategies and to identify unresolved challenges in achieving controlled weld root geometry for high-integrity piping applications. Recent industrial failure investigations, particularly in ethylene oxide service piping, further underscore the importance of weld root control. Several documented leak events were traced to excessive root protrusion and inadequate interpretation of non-destructive testing data, where elevated reinforcement disrupted internal flow and promoted turbulence-induced degradation. These recurring issues highlight a broader industry challenge and strengthen the need for improved root-height optimization in critical piping applications. A significant research gap is identified in the limited optimization of weld root reinforcement, particularly in gas tungsten arc welding processes, where most reported studies document root heights exceeding 3 mm. Achieving a root height below 2 mm, which is an important requirement for reducing flow-induced turbulence and meeting industry acceptance criteria, remains insufficiently addressed. This review highlights this gap and outlines future research opportunities involving advanced parameter optimization and improved process monitoring techniques. The synthesis presented here provides a comprehensive reference for enhancing weld quality in critical piping systems and establishes a pathway for next-generation welding strategies aimed at producing high-integrity weld joints compliant with the American Society of Mechanical Engineers B31.3 requirements. Full article

This study examines the through-thickness microstructure and crystallographic texture evolution in friction-stir-welded (FSWed) AA5052-H32 and AA6061-T651 aluminum alloys using a tri-flats threaded pin tool. Optical microscopy and electron backscatter diffraction (EBSD) were employed to characterize grain morphology, boundary misorientation, and texture components across the weld thickness. Both alloys exhibited progressive grain refinement and increased high-angle grain boundary fractions from the top to the bottom of the stir zone due to combined thermal and strain gradients. The FSWed AA5052 displayed dominant {111}<110> and Y + γ fiber components at the upper and mid regions, whereas AA6061 showed more randomized textures. At the bottom region, both alloys developed rotated Goss {011}<01-1> and weak A ({112}<110>) and α fiber components. These results clarify how alloy strengthening mechanisms—solid-solution versus precipitation hardening—govern texture evolution under different strain-path and heat input conditions. The findings contribute to optimizing process parameters and material selection for structural-scale FSW aluminum joints in industrial applications such as bridge decks, transportation panels, and marine structures. Full article

Molten pool flow and keyhole status during Variable Polarity Plasma Arc (VPPA) welding directly affect the weld quality and stability. The lack of a clear correlation between them, however, prevents this process approach from being developed further. To investigate the keyhole morphology and liquid metal flow, the experimental examination of fluid flow by the X-ray imaging method and numerical simulation of plasma arc under the effect of the keyhole were carried out. By changing the tungsten electrode setback while keeping all other parameters, it is possible to vary the keyhole status and maintain the consistency of heat input to the base metal. This work establishes a dual-bifurcation flow model to characterize the keyhole molten pool, where the bifurcation point on the keyhole rear wall significantly affects the stability of the keyhole molten pool. The rear wall of the keyhole is divided into three sections from top to bottom, with the arc pressure in the middle section being significantly higher than in the upper and lower sections. As the degree of arc constriction increases—i.e., as arc stiffness or arc force increases—the middle section becomes more vertical. By the calculated distribution of driving forces, the arc pressure has a high possibility of being one of the dominances for the metal flow in keyhole welding of aluminum alloys. Arc pressure is also important for the bifurcation point position, which is closely related to the three welding states: blind keyhole, keyhole, and cutting. Full article

This paper reviews tab-to-busbar interconnections in lithium-ion battery packs, focusing on resistance welding (RW), laser beam welding (LBW), and ultrasonic welding (USW). The functional roles of tabs and busbars and typical material choices (Al-, Cu-, and Ni-plated Cu) are outlined. Subsequently, the processes are compared in terms of heat input, interfacial metallurgy, electrical resistance, mechanical robustness, and manufacturability. USW, as a solid-state method, suppresses porosity and limits Al-Cu intermetallic growth, but is sensitive to thickness, stack geometry, and tool wear. LBW enables high-speed, automated production with precise energy delivery, yet requires careful control to mitigate spatter, porosity, and brittle IMCs in dissimilar joints. RW remains cost-effective and flexible but can suffer from electrode wear and variability with highly conductive stacks. This review also summarizes the effect of the busbar material (Al versus Cu) and thickness on the connection resistance and temperature increase under a high current. No single process is universally superior, and the selection should match the stack-up, reliability targets, and production constraints. This paper aims to provide an overview of recent and conventional research trends for each welding method and to introduce selected non-traditional approaches, thereby presenting a range of viable options for future applications. Full article

Solidification cracking is a critical defect in Cu–steel dissimilar laser welding for cylindrical lithium-ion battery busbar assembly, yet the metallurgical role of phosphorus (P) in crack formation has not been quantitatively established. In this study, the influence of phosphorus in the coating layer on weld solidification behavior was clarified by preparing Cu substrates with four different coating conditions—Ni–P-coated Cu (10 and 50 μm) and pure Ni-coated Cu (10 and 50 μm)—and performing high-speed single-mode fiber-laser welding under identical heat-input conditions. Shear-tensile testing, EPMA-based microstructural analysis, and Thermo-Calc solidification calculations were combined to correlate P segregation with solidification cracking susceptibility. The Ni–P 10 μm coating generated severe solidification cracking compared with the pure Ni 50 μm coating, which was attributed to excessive P enrichment in the terminal liquid phase (up to 8.8 mass%). This enrichment significantly expanded the mushy-zone width to approximately 869 K, yielding a highly solidification crack-susceptible fusion zone. In contrast, 50 μm pure Ni coatings produced narrow mushy-zone widths (200–400 K) and extremely low residual P levels (~0.1 mass%), resulting in fully crack-free microstructures. The 50 μm Ni coating exhibited the highest shear-tensile strength and largest rupture displacement among all conditions, confirming that suppression of P segregation directly improves both structural integrity and mechanical performance. Overall, this study demonstrates that phosphorus enrichment critically governs the solidification-cracking susceptibility of Cu–steel dissimilar welds by widening the solidification temperature range. Eliminating P from the coating layer and applying an adequately thick pure Ni coating constitute highly effective strategies for achieving crack-free, mechanically robust welds in lithium-ion battery busbar manufacturing. Full article

This study explores Friction Stir Spot Welding (FSSW), a well-established solid-state joining technique, for high-strength aluminum alloys like AA2024-T4, which present significant challenges for conventional welding techniques. This research focuses on the impact of relatively low rotational speeds, specifically within a range of 700 to 1300 rpm, on the mechanical and microstructural properties of the welded joints. By employing a short dwell time of 3 s, this study aims to enhance productivity in the automotive and aerospace industries. The experimental work evaluated the joints’ thermal cycles, macrostructure, microstructure, hardness and load-carrying capacity. Results indicated a linear relationship between rotational speed and heat input. Although all welds exhibited a significant grain size reduction in the stir zone (SZ) compared to the base material (29.7 ± 6.1 μm), the SZ grain size increased with rotational speed, ranging from 4.7 ± 1.4 to 8.3 ± 1.3 μm. This study identified 900 rpm as the optimal parameter, achieving the highest load-carrying capacity (7.35 ± 0.4 kN) and a high SZ hardness (99 ± 1.5 HV). These findings confirm that joint strength is a balance between grain refinement and thermal softening. The presence of precipitates and the fractography of the tensile–shear tested specimens were also investigated and discussed. Full article

Coarse grains and blocky M-A constituents are often generated in the heat-affected zone (HAZ) of fusion welded pipeline steel joints owing to high heat input, causing a significant deterioration of toughness. This study demonstrated the effect of heat input in friction stir welding (FSW) on the microstructure and toughness of the nugget zone (NZ), elucidating the microstructure evolution and toughening mechanism. The results revealed a marked reduction in effective grain size within the NZ at low heat input (LHI) and a significant increase in the ratio of the refined M-A constituent. Furthermore, the decreased heat input leads to weak texture components (D1, D2, and F) accompanied by a decrease in the kernel average misorientation (KAM) value. This microstructural optimization clearly enhances toughness, and an excellent toughness value of 200 J, representing 95.3% of the basal metal (BM), was achieved in the NZ at LHI. The primary reason for this improvement is the refinement of effective grains and M-A constituents resulting from reduced heat input. During crack propagation, the high proportion of effective grain boundaries and fine M-A constituents acts as a barrier, arresting and deflecting cracks and thereby enhancing toughness. Full article

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

High-strength S690 steel is becoming increasingly popular in Hong Kong because of its numerous advantages in terms of mechanical properties and cost-effectiveness. Compared to normal-strength steel, the welding parameters such as preheat temperature, inter-pass temperature, and heat input energy of high-strength S690 steel should be controlled more strictly; additional post-weld heat treatment should be carried out for hydrogen diffusion in some situations. These strict requirements pose challenges to welding operations at construction sites. In Hong Kong, all field connections of high-strength S690 steel components are made using bolted connections, and there are currently no precedents for welded connections on site. To verify the reliability of on-site welding and optimize the welding process to facilitate operation, on-site welding tests of high-strength S690 steel with various welding procedures were conducted. These welding tests were first performed on the steel plates, followed by tests on the H-section steel components, to examine the mechanical reliability of the welding connections under tension and compression. The effects of heat input energy, welding joints, post-weld heat treatment, and wind blocking measures on welding quality and welding efficiency were studied. Full article

The purpose of this paper is to study the weldability of two specific steels, UNS S31803 (duplex) and UNS S 32760 (super duplex), by making heterogeneous butt joints using gas tungsten arc welding technology. These materials are widely used in applications that take advantage of their superior corrosion resistance, strength, or both, such as chemical plants, oil and gas equipment, offshore sector, marine and other high-chloride environments. Although the joining technique of DSS and SDSS steels is a well-established industrial method, there are several process parameters that can play a key role in the correct execution of welds and in their final achievable properties. Starting from this assumption, this paper investigates some specific aspects such as the influence of heat input and shielding gas composition on the joint’s microstructure and the consequent changes in the ferrite/austenite ratio, also after post-welding heat treatments. Effects on both mechanical and corrosion resistance properties of the alloys are addressed. Full article

The low-temperature impact properties of high-heat-input steels, particularly low-carbon Nb–Ti steel, are significantly influenced by the coarse-grained heat-affected zone (CGHAZ) in welded joints. The microstructure predominantly consists of granular bainitic ferrite (GBF), ferrite side plate (FSP), degenerate pearlite (DP), coarse plate-like ferrite (PF), and limited acicular ferrite (AF). This study investigates the effect of lanthanum (La) addition to Nb–Ti steel, leading to the formation of composite inclusions with a LaAlO₃·TiN core surrounded by MnS/MnC precipitates. Unlike conventional Al₂O₃·MnS inclusions in Nb–Ti steel, these La-modified inclusions promote enhanced AF nucleation. This not only refines prior austenite grains but also reduces detrimental microstructural constituents such as GBF and FSP. As a result, the impact energy at −40 °C significantly improves from 23 J (Nb–Ti steel) to 137 J (Nb–Ti–La steel). Moreover, the inclusions exhibit an increase in size but a decrease in number density. The Nb–Ti–La variant demonstrates a higher AF volume fraction and increased AF density within the CGHAZ. The refined grain structure, along with an increased proportion of high-angle grain boundaries, effectively impedes secondary crack propagation. These microstructural modifications contribute to a substantial improvement in the low-temperature impact toughness of welded joints. Full article

This study systematically investigates the effects of welding current on the macro-morphology, microstructure, mechanical properties, and corrosion resistance of Cu-Mn-Al alloy coatings deposited on 27SiMn steel substrates using Cold Metal Transfer (CMT) technology. The 27SiMn steel is widely applied in coal mining, geology, and engineering equipment due to its high strength and toughness, but its poor corrosion and wear resistance significantly limits service life. To address this issue, a Cu-Mn-Al alloy (high-manganese aluminum bronze) was selected as a cladding material because of its superior combination of mechanical strength, toughness, and excellent corrosion resistance in saline and marine environments. Compared with conventional cladding processes, CMT technology enables low-heat-input deposition, reduces dilution from the substrate, and promotes defect-free coating formation. To the best of our knowledge, this is the first report on the fabrication of Cu-Mn-Al coatings on 27SiMn steel using CMT, aiming to optimize process parameters and establish the relationship between welding current, phase evolution, and coating performance. The experimental results demonstrate that the cladding layer width increases progressively with welding current, whereas the layer height remains relatively stable at approximately 3 mm. At welding currents of 120 A and 150 A, the cladding layer primarily consists of α-Cu, κII, β-Cu₃Al, and α-Cu + κIII phases. At higher welding currents (180 A and 210 A), the α-Cu + κIII phase disappears, accompanied by the formation of petal-shaped κI phase. The peak shear strength (509.49 MPa) is achieved at 120 A, while the maximum average hardness (253 HV) is obtained at 150 A. The 120 A cladding layer demonstrates optimal corrosion resistance. These findings provide new insights into the application of CMT in fabricating Cu-Mn-Al protective coatings on steel and offer theoretical guidance for extending the service life of 27SiMn steel components in aggressive environments. Full article

Heat source parameters are critical input variables in welding thermal analysis, directly and significantly affecting the accuracy of the temperature field distribution, welding distortion, and residual stress prediction. This is particularly important in safety-critical welded structures, where high-precision heat source parameter identification is essential for ensuring the thermal simulation accuracy and mechanical performance reliability. Traditional parameter identification methods based on finite element simulations or experiments have limitations in adapting to complex working conditions and variable environments. To address this, this paper proposes the Heat Source Parameter Identification Network (HSPINet) model based on a residual convolutional neural network (ResNet) architecture with an attention mechanism capable of extracting key features from the weld morphology of T-joint structures, while accounting for the influence of process parameters and joint dimensions to achieve efficient and accurate identification of heat source parameters. This study not only enhances the intelligence level of heat source parameter identification but also provides a practical, intelligent tool for welding simulation and thermal field evaluation in complex industrial applications, demonstrating significant theoretical value and broad applicability in laser processing and manufacturing scenarios. Full article

Welded structures, such as offshore platforms, require robust toughness in their heat-affected zones (HAZ) to withstand low-temperature environments. The coarse-grained HAZ (CGHAZ) adjacent to the fusion boundary often exhibits reduced toughness due to grain coarsening, particularly under high heat input welding conditions aimed at enhancing productivity. To address this, high-nitrogen steels containing TiN particles were developed to suppress austenite grain growth by leveraging the thermal stability of TiN precipitates. Three high-nitrogen steels with varying carbon contents (0.09%, 0.11%, and 0.15%) were fabricated and subjected to crack tip opening displacement (CTOD) testing at −20 °C and −40 °C to evaluate low-temperature HAZ toughness. Results indicate that high-nitrogen TiN steels exhibit superior CTOD values (1.38–2.73 mm) compared to conventional 490-MPa class steels, with no significant reduction in toughness despite increased carbon content. This is attributed to the presence of stable TiN particles, which restrict austenite grain growth during welding thermal cycles, and the formation of fine ferrite–pearlite microstructures in the HAZ. These findings highlight the efficacy of high-nitrogen TiN steels in enhancing low-temperature fracture resistance for welded structures. Full article