Mathematical analysis using the Kaltenhauser factor was performed to determine the maximum allowable contribution of 309L austenitic stainless steel (ASS) filler to Ti–Nb-stabilized AISI 441 ferritic stainless steel (FSS) base metal (BM) in arc-based fusion welding for achieving martensite-free welds. The model predicted a threshold of 4.61 wt.% filler. However, gas tungsten arc welds fabricated at low heat input (LHI) and high heat input (HHI) revealed duplex austenite–delta ferrite microstructures even at higher filler contributions. This deviation was attributed to the presence of Ti-, Nb- and Cr-rich carbides in the weld. Optical microscopy and X-ray diffraction confirmed duplex microstructures, with LHI producing a finer phase distribution and HHI showing localized austenite pockets. Both weldments exhibited a higher ultimate tensile strength and a small decrease in ductility compared to FSS BM, further supporting the absence of martensite. Investigation indicates that incorporating Nb in Kaltenhauser factor would enhance its reliability in predicting the maximum ASS filler contribution below which a martensite formation in FSS weld can be avoided. Furthermore, a generalized equation was developed to predict the maximum ASS filler contribution in any FSS BM, enabling martensite-free weld.

A systematic parametric study was conducted on ultrasonic welding between commercially pure titanium and low-carbon St12 steel to examine the influence of welding pressure (4–7 bar) and welding time (1–3 s) at a constant frequency of 20 kHz and fixed power. The welded joints were characterized by OM, SEM, EDS mapping and line scans, Vickers microhardness, and shear tensile testing. A bonding threshold was observed at lower pressure–time combinations, while optimum performance was achieved at 7 bar and 2.5 s, producing a maximum shear strength of 111 MPa. On the steel side, dynamic recrystallization and grain coarsening were observed, whereas the titanium side exhibited localized α→β transformation and the formation of acicular α′ structures under higher heat input. Localized material flow and vortex-like mechanical interlocking were evident, accompanied by titanium diffusion into steel up to approximately 5.5 µm. No continuous intermetallic layer was detected by SEM/EDS analysis. Microhardness increased in martensitic titanium regions, reaching values of about 264 HV, and varied on the steel side according to recrystallization. Fractographic examination of the optimum sample revealed ductile dimples, confirming a ductile failure mode. The results demonstrate that ultrasonic welding can reliably produce robust Ti/St12 joints.

This study investigates the robotic resistance spot welding (RRSW) behavior of a dissimilar three-layer aluminum–steel–aluminum stack, focusing on how variations in current, weld time, and secondary pulse modulation influence weld penetration, interfacial microstructure, and mechanical performance. Taguchi L9 experimental matrix was employed to plan experimentations under controlled electrode force and pulse conditions. Weld penetration depth was found to increase consistently with thermal input, transitioning from sub-critical interfacial fusion to full-thickness nugget formation. However, excessive energy input led to over-penetration, weld asymmetry, and expulsion, highlighting the need for thermal input optimization. Microhardness profiling across weld zones revealed an inverse correlation between overall fusion zone hardness and increasing heat input, although localized hardness enhancements were observed under specific pulse configurations. Optimal mechanical performance was achieved under mid-range energy inputs, where thin and uniform IMC layers (1–3 µm) provided sufficient interfacial strength without inducing brittleness. The findings underscore the importance of pulse shaping and thermal control in managing interfacial reactions and solidification kinetics during dissimilar metal welding. The study offers insights for optimizing RRSW in multi-material stacks, emphasizing that joint reliability depends not solely on weld size or hardness, but on achieving a precise balance between metallurgical bonding and thermal moderation.

The present study evaluates the mechanical behavior of a wire arc additively manufactured dis-similar stainless-steel wall composed of alternating SS304 and SS308L layers. The experimentally obtained tensile data were converted to true stress-strain values and accurately modeled using the modified Ramberg-Osgood (RO) relation. The dissimilar material wall (DMW) exhibited a yield strength of 354 MPa and an ultimate tensile strength (UTS) of 622 MPa, both superior to those of the individual base alloys. The RO model effectively captured the nonlinear deformation characteristics, yielding coefficients of determination (R2) of 0.9198, 0.9596, and 0.9714 for DMW, SS304, and SS308L, respectively. Microstructural analysis revealed distinct grain morphology transitions at the interface, influencing localized mechanical performance. Fractography confirmed a ductile failure mode consistent with the predicted true stress–strain response. Overall, the study establishes that DMW demonstrates enhanced strength and ductility, validating the applicability of the modified RO model for accurate deformation prediction in additively manufactured multi-material structures.

The present study reports the effect of two explosive thicknesses (38 mm and 47 mm) on the interface microstructure and hardness of multilayered explosive-welded composites comprising 1050 aluminum, 5052 aluminum, and AZ31 magnesium. The interface between the dissimilar aluminum alloys remains straight, whereas the 5052 Al/AZ31 interface exhibits a wavy morphology with trapped jet formation. For the 38 mm explosive thickness, the interfacial waves are stable, with amplitude ranging from 151 to 173 µm, wavelength from 831–919 µm, and an amplitude-to-wavelength ratio between 0.17 and 0.20. In contrast, with the 47 mm explosive, the waves become unstable, as amplitude (93–211 µm), wavelength (459–938 µm), and amplitude-to-wavelength ratio (0.15–0.24) show wider variation. Hardness measurements reveal localized strengthening near both interfaces. For the 38 mm condition, maximum Vickers micro-hardness values of 51.3 HV and 92.0 HV are observed closer to the first interface, while values of 96.2 HV and 124.1 HV are witnessed near the 5052 Al/AZ31 interface. Under the 47 mm condition, 51.3 HV and 92.3 HV are recorded about 20 µm away from the dissimilar aluminum interface, with higher hardness values of 97.8 HV and 125.2 HV attained at the 5052 Al/AZ31 interface due to greater plastic deformation.

This study investigates microcracks and lack of sidewall fusion in API 5 L X70M grade submerged-arc welded (SAW) pipes using nondestructive testing (NDT) methods. Through metallographic analysis and advanced NDT techniques, including ultrasonic testing (UT), radiographic testing (RT), and phased array ultrasonic testing (PAUT), the origins and impacts of these defects on pipeline integrity are examined. The results reveal that slag entrapment and improper fusion, stemming from welding process inconsistencies, are primary causes. The findings provide actionable insights into prevention strategies, such as optimized welding parameters and enhanced quality assurance measures, for ensuring the reliability of high-strength pipeline steels.

This study investigates the Pulsed Current Gas Tungsten Arc Welding (PCGTAW) of ASME SA 106 low-carbon steel pipes, used in steam boiler membrane walls. Pipes of 50 mm diameter and 5 mm thickness are welded using a 1.5 mm root gap, 1 mm land and 30° chamfer. The root pass used 1.2-mm ER70S2 filler wire, and the final pass used 2.5-mm wire. The key parameters, namely pulse current, background current, frequency and pulse-on time, are optimized using a Taguchi L9 orthogonal array and ANOVA. Optimal settings are 200 A pulse current, 100 A background current, 4 Hz frequency and 50% pulse-on time. The resulting welds exhibited an ultimate tensile strength of 469.46 N/mm2 (14% higher than base metal) and an impact strength of 116 J (10% lower) than base metal. Microstructure reveals acicular and polygonal ferrite, carbides and pearlite. Microhardness is 205 HV. Fractography indicates ductile failure. XRD revealed Fe, Fe3 C and Fe4 C phases; EDAX showed Cr and Si, contributing to strength. Corrosion analysis reveals slight increase in weld area corrosion rate (0.026662 mm/year) compared to the base metal (0.022601 mm/year). Overall, optimized PCGTAW yields strong, reliable joints suitable for pressure vessel.

The activity coefficients of Zn component in Zn-Ag-Cu, Zn-Au-Cu and Zn-Ni-Cu ternary solid alloys were predicted using the Molecular Interaction Vacancy Model (MIVM) with three distinct parameterization approaches: experimental activity fitting, liquid–solid equilibrium analysis, and the infinite dilution activity coefficient method. Results demonstrate that predictions derived from the infinite dilution activity coefficient method exhibit superior agreement with experimental values. For the Zn-Ag-Cu system at 1000 K, this method achieved an average relative error of 7.13% for Zn activity coefficients, significantly outperforming the experimental activity fitting and liquid–solid equilibrium analysis. Similar accuracy trends were observed across all ternary systems, with the infinite dilution activity coefficient method consistently yielding the lowest deviations (≤7.13%). This systematic comparison conclusively identifies the infinite dilution activity coefficient method as the optimal strategy for obtaining the pair potential interaction parameters (The B parameters) within the MIVM framework, thereby enhancing the model’s predictive reliability for thermodynamic assessments of solid alloy systems.

Cold metal transfer welding, or CMT, a modified form of metal inert gas (MIG) welding, is a low heat-input and low-spatter process. However, short plasma duration (Tp) and high boost current (Ib) result in spatters that create volumetric defects in the weld deposits. This study aims to minimize spatter by optimizing Tp and Ib for the bead-on-plate deposition of 316L stainless steel (SS) on 304L SS base plate. Both parameters are varied one at a time, and the percentage of the voltage waveform with spatter is calculated. It is observed that, for a wire feed (WF) rate of 6 m/min and a welding speed (WS) of 0.6 m/min, increasing Tp from 6.8 ± 2.6 to 15 ± 3 ms decreases the spatter waveform from 21 to 4%. Similarly, reducing Ib from 303 ± 29 to 226 ± 17 A reduces the spatter waveform from 18.5% to 6.5%. Further, bead-on-plate trials are performed by varying the WS from 0.12 to 0.6 m/min, while maintaining a constant WF rate of 6 m/min, with an optimum Tp and Ib of 14 ± 3 ms and 240 ± 20 A, respectively. These changes maintain the spatter waveform within 5% across different weld speeds and result in minimal volumetric defects.

The broad industrial adoption of friction stir welding (FSW) for hard alloys and thick aluminium plates is limited by several challenges: (i) selection of appropriate tool material and design, (ii) low welding efficiency/productivity, and (iii) premature tool failure. To address these issues, this study presents a finite element (FE) analysis of a laser-FSW hybrid welding technique. Thermal analysis is conducted for a 3.2 mm thick S45C steel plate using two moving heat sources. A negative moving heat source simulates the backing plate effect in the high-pressure region beneath the FSW tool. The results demonstrate that a duplex microstructure (Ferrite + retained Austenite/Martensite) can be achieved using the hybrid approach. For thick 5083-O aluminium alloy (AA) plates, the hybrid technique enables an increase in welding speed from 100 to 200 mm/min without causing tool failure, thereby improving productivity. The numerical modelling of the laser-FSW hybrid system for AA 5083-O is carried out in two sequential steps: first, laser preheating is simulated; then, tool plunging is performed on the preheated plate. The resulting Von Mises stress distribution confirms that laser-assisted preheating reduces stress during the initial tool plunge, enhancing tool life and ensuring the viability of the hybrid process for welding thicker materials.