Search Results (17)

This paper deals with the influence of micro-pulsed direct current on microstructure and mechanical properties of gas tungsten arc welding (GTAW) weldments of Ti-6Al-4V (Ti-64). Bead-on-plate GTA welds were made on the samples in the un-pulsed and micro-pulsed (125 Hz and 250 Hz) conditions. Post-weld heat treatment (PWHT) was performed on a few coupons at 700 °C for 3 h in an inert atmosphere, followed by furnace cooling. In the microstructure, the fusion zone (FZ), base metal (BM), and heat-affected zone (HAZ) can be easily distinguished. The top surface of the FZ has large columnar grains because of lower heat loss to the surrounding atmosphere, and the bottom region of the FZ has comparatively smaller equiaxed grains. The micro-pulsed samples’ FZ grain size was lower than that of those made without pulsing. This shows that high-frequency current has substantially refined prior β grains. The microstructure of the FZ is characterized by an acicular morphology composed of α, martensitic α′, and retained β phases. The FZ’s hardness was higher than the BM due to the presence of martensitic α′. Additionally, the hardness in the HAZ was elevated due to the formation of finer martensitic α′. Micro-pulsed DC welding led to improved mechanical properties, including higher hardness, ultimate tensile strength (UTS), and ductility compared to un-pulsed welding. This enhancement is attributed to the grain refinement achieved with micro-pulsed DC. After PWHT, the prior β grain size remained relatively unchanged compared to the as-welded condition. However, the hardness in the FZ decreased due to the decomposition of α′ into α and β phases. The ductility of all samples improved as a result of the widening of the diffusional α phase. Full article

In this study, 316L austenitic stainless-steel (ASS) plates fabricated using an additive manufacturing (AM) process were joined using tungsten inert gas (TIG) and laser welding techniques. The 316L ASS plates were manufactured using a laser powder bed fusion (LPBF) technique, with building orientations (BOs) of 0° and 90°, designated as BO-0 and BO-90, respectively. The study examined the relationship between indentation resistance and microstructure evolution within the fusion zone (FZ) of the welded joints considering the effects of different BOs. Microstructural analysis of the weldments was conducted using optical and laser confocal scanning microscopes, while hardness measurements were obtained using a micro-indentation hardness (H_IT) technique via the Berkovich approach. The welded joints produced with the TIG technique exhibited FZs with a greater width than those created by laser welding. The microstructure of the FZs in TIG-welded joints was characterized by dendritic austenite and 1–4 wt.% δ-ferrite phases, while the corresponding microstructure in laser-welded joints consisted of a single austenite phase with cellular structures. Additionally, the grain size values of FZs produced using the laser welding technique were lower than those produced using the TIG technique. Therefore, TIG-welded joints showcased hardness values lower than those welded by laser welding. Furthermore, welded joints with the BO-90 orientation displayed the greatest cooling rates following welding processing, leading to FZs with hardness values greater than BO-0. For instance, the FZs of TIG-welded joints with BO-0 and BO-90 had H_IT values of 1.75 ± 0.22 and 2.1 ± 0.09 GPa, whereas the corresponding FZs produced by laser welding had values of 1.9 ± 0.16 and 2.35 ± 0.11 GPa, respectively. The results have practical implications for the design and production of high-performance welded components, providing insights that can be applied to improve the efficiency and quality of additive manufacturing and welding processes. Full article

The fabrication of welded joints in steel sheets has become a focal point, especially in meeting the demands for interconnections within battery packs for electric vehicles (EVs). This study delves into the impact arising from the initiation arc during the micro-tungsten inert gas (TIG) welding of nickel-plated steel sheets. The investigation involved the manipulation of various current modulations and arc lengths. Notably, optimal results were achieved with a 5 mm arc length paired with a 25 A current modulation. Microstructural analysis, conducted through scanning electron microscopy (SEM), unveiled a higher penetration depth, contributing to a more extensive and shallower fusion zone at the interface between the filler metal and the base material. Tensile testing revealed impressive mechanical properties, with the ultimate tensile strength peaking at 90 N/mm², a yield strength of 85 N/mm², and the highest elastic modulus. This underscores the weld’s robustness in withstanding applied loads and resisting fracture. Furthermore, the calculation of the lowest K factor at 1.0375 indicated a reduction in resistance across the specimen, resulting in enhanced conductivity. Micro-TIG welding emerges as an efficient method for nickel-plated steel in connecting individual battery cells to form a high-capacity battery pack. These interconnections ensure efficient current flow and maintain the overall integrity and performance of the battery pack. The reliability and quality of these interconnects directly affect the battery’s efficiency, safety, and lifespan in EVs application. Full article

The success of laser communications heavily relies on the stiffness, dynamic properties, static performance, and manufacturability of the U-frame. The U-frame is a fundamental element in satellite-to-ground laser communication telescopes. However, there is currently a lack of research on the optimal design of U-frames, leading to a significant gap between ideal construction and practical manufacturability. To address these concerns, this study proposes a comprehensive approach that combines multi-objective topology optimization and multi-start size optimization techniques. This approach considers the multidisciplinary constraints imposed by mechanical, control, and optical systems. The objective is to achieve both the conceptual and detailed design of a novel U-frame, while also ensuring thorough consideration of the structure’s manufacturability during the optimization process. The prototype of the optimized U-frame was successfully fabricated using laser welding processes. The tensile test conducted on the prototype supported the idea that laser welding can enhance the micro-grain size of the joint, leading to improved overall mechanical properties. In particular, the joint strength achieved through laser welding was found to be 1.5 times greater than that achieved through TIG (Tungsten Inert Gas) welding. Additionally, the results obtained from the free vibration experiment closely aligned with the simulation, confirming the feasibility of manufacturing the optimized structure. The optimized structure demonstrated an improvement of 7.13% in dynamic performance and 29.61% in static performance compared to the first-generation structure. Additionally, there was a reduction of 29.89% in mass without affecting the remaining performance aspects. The successful fabrication of the prototype validates the feasibility of the proposed welding process and highlights the superiority of the new U-frame. Full article

The International Thermonuclear Experiment Reactor (ITER) Thermal shield (TS) serves as a cryogenic heat exchanger to maintain the thermal stability of the ITER superconducting magnet coil, which is critical to the control of the plasma during the operation of the ITER device. The TS is composed of long-length 316L stainless steel (SS) and copper as brazed joints. In this case, a feasible fabrication design for the CCS TS is presented, accomplished by three kinds of joining processes (vacuum brazing, friction stir weld, and TIG weld). In the reliable fabrication design, the brazing quality of the as-brazed long-distance 316L SS and copper joints plays a critical role in the thermal conductivity performance of the ITER thermal shield. Therefore, a high-quality vacuum brazing process of long-length SS/Cu joints applied in a low-temperature superconductor magnet system was first studied. The macro metallography analysis demonstrates the braze ratio of the samples is 100%, and no crack or defect is observed in the samples. The microstructural characterization reveals the brazing seams are composed of silver-based Ag-rich eutectic. The micro-shear test indicates that the shear strength of the 316L tube and copper joint is 205 MPa, with the fracture position located on the copper side; this zone will be the most vulnerable zone of the joints. In addition, the SEM results illustrated that the shear fracture morphology displayed a ductile fracture feature. The test results demonstrated that the highly precise depth drilling employed in this paper ensured a good control of the brazing clearance, resulting in a 100% braze ratio for the long-length SS/Cu joints. Therefore, it can be concluded that the brazing process can be applied in the ITER TS for the good thermal conductivity performance of long-length SS/Cu-brazing joints. Full article

TIG arc additive manufacturing experiments were performed utilizing TiB₂ nanoparticle-reinforced toward to 7075 aluminum alloy welding wire, and the microstructure and mechanical properties corresponding to different locations of welding plate were investigated. At the top location of the deposited layer, the microstructure was characterized by fine dendrite induced by solidification, and equiaxed grain was predominant at the middle location. The grain size at the bottom location was obviously larger compared to the top and middle locations, and secondary-phase particles were homogeneously distributed at the grain boundary or inner grains. The mechanical properties at the top location of the deposited layer were most excellent compared to the middle and bottom locations, and the tensile properties and micro-hardness were decreased with the detected area varying from middle location to the bottom location. The excellent combination of fracture elongation and maximum of tensile strength corresponding to different locations on the deposited layer were determined to be 361.8 MPa with respect to the 7075 aluminum alloy welding wire, respectively, which was higher compared to the samples processed by general arc additive manufacturing process with tensile strength of (279.4 ± 5.3) MPa, indicating the TiB₂ nano-sized particles possessed certain enhancing effects on the investigated 7075 aluminum alloy. Full article

The inspection of the quality of welds in battery packs plays an important role in ensuring safety during the manufacturing and operation of energy-storage devices in automotive vehicles during service. This research investigated the novel application of laser Doppler vibrometry, a widely used non-destructive optical technique for modal analysis, to the post-weld evaluation of micro-TIG-welded interconnections in lithium-ion supercells. The experimental modal analysis showed features in the modal models of the supercells that were unique to their welding conditions. The comparisons between the supercells showed an absence of linear correlations between the modal parameters and the welding current, as well as differences in the welding parameters obtained from the negative and positive terminals of the cylindrical cells. These findings suggested that the modal parameters of the supercells were more strongly influenced by the rigidity of the structural materials than by the localized compliance of the welded interconnections. While this investigation demonstrated a method for using laser Doppler vibrometry to distinguish between different welding conditions in lithium-ion supercells at a structural level, further development is needed to identify the weld quality of individual interconnections. Full article

In this work, AA1070 aluminium alloy sheets are joined using TIG and MIG welding after three different edge preparations. Shearing, water jet and plasma-cut processes were used to cut sheets, subsequently welded using ER5356 and ER4043 filler metals for TIG and MIG, respectively. Mechanical properties of the obtained sheets were assessed through tensile tests obtaining a relation between sheet preparation and welding tightness. Micro-hardness measures were performed to evaluate the effects of both welding and cutting processes on the micro-hardness of the alloy, highlighting that TIG welding gives rise to inhomogeneous micro-hardness behaviour. After tensile tests, surface fractures were observed employing scanning electron microscopy to highlight the relation between tensile properties and edge preparations. Fractures show severe oxidation in the water jet cut specimens, ductile fractures and gas porosities. Full article

A lightweight, highly corrosive resistant, and high-strength wrought alloy in the aluminum family is the Aluminium 8006 alloy. The AA8006 alloy can be formed, welded, and adhesively bonded. However, the recommended welding methods such as laser, TIG (Tungsten Inert Gas welding), and ultrasonic are more costly. This investigation aims to reduce the cost of welding without compromising joint quality by means of friction stir welding. The aluminum alloy-friendly reinforcement agent zirconia is utilized as particles during the weld to improve the performance of the newly identified material AA8006 alloy in friction stir welding (FSW). The objectives of this research are to identify the level of process parameters for the friction stir welding of AA8006 to reduce the variability by the trial-and-error experimental method, thereby reducing the number of samples needing to be characterized to optimize the process parameters. To enhance the quality of the weld, the friction stir processing concept will be adapted with zirconia reinforcement during welding. The friction stir-processed samples were investigated regarding their mechanical properties such as tensile strength and Vickers microhardness. The welded samples were included in the corrosion testing to ensure that no foreign corrosive elements were included during the welding. The quality of the weld was investigated in terms of its surface morphology, including aspects such as the dispersion of reinforced particles on the welded area, the incorporation of foreign elements during the weld, micro defects or damage, and other notable changes through scanning electron microscopy analysis. The process of 3D profilometry was employed to perform optical microscopy investigation on the specimens inspected to ensure their surface quality and finish. Based on the outcomes, the optimal process parameters are suggested. Future directions for further investigation are highlighted. Full article

Low pressure turbine rotors are manufactured by welding thick sections of 25Cr2Ni2MoV rotor steel using tungsten inert gas (TIG) backing weld, and submerged arc welding (SAW) filling weld. In this study, the microstructure of columnar grain zones and reheated zones in weld metal was characterized meticulously by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Electron Back-Scatter Diffraction (EBSD). The results showed that, compared with SAW weld metal microstructure, TIG weld metal microstructure was relatively fine and homogeneous, due to its lower heat input and faster cooling rate than SAW. The maximum effective grain size in TIG and SAW weld were 7.7 μm and 13.2 μm, respectively. TIG weld metal was composed of lath bainite (LB) and blocky ferrite (BF), while SAW weld metal was composed of acicular ferrite (AF), lath bainite (LB)and ferrite side plate (FSP). Tempered martensite (TM) was detected along columnar grain boundaries in both TIG and SAW weld metals, which was related to the segregation of solute elements during weld solidification. Electron Probe Micro-Analysis (EPMA) results showed that the contents of Ni and Mn at the dendritic boundaries were 50% higher than those at the dendritic core in TIG weld. Similarly, 30% of Ni and Mn segregation at dendritic boundaries was also found in SAW weld. In addition, the microhardness of the two welded joints was tested. Full article

A semi-solid stir casting mixed multi-pass rolling process was successfully employed to manufacture TiCp/Al-5Mg composite filler wires with different contents of TiC particles. The 5083-H116 aluminum alloys were joined by tungsten inert gas (TIG) using TiCp/Al-5Mg composite weld wires. The microstructure, mechanical properties, fractography and corrosion behavior of the welds were evaluated. The results revealed that TiC particles were distributed in the welds uniformly and effectively refined the primary α-Al grains. The hardness and tensile strength of the welds were improved by increasing the TiC particle content, which could be attributed to the homogeneous distribution of TiC particles and the microstructure in the weld joints. Potentiodynamic polarization testing revealed that the corrosion resistance of the welds also increased with the addition of TiC particle contents. In addition, the stress corrosion cracking (SCC) susceptibility of the welds decreased as micro-TiC particles were introduced into the welds. The electronic structure of the Al/TiC interface was investigated by first principle calculation. The calculation showed that valence electrons tended to be localized in the region of the TiC-Al interface, corresponding to an addition of the overall work function, which hinders the participation of electrons in the composite in corrosion reactions. Full article

The surface of Q235 low carbon steel was modified by the metal inert-gas welding (MIG) method; a 304 stainless steel surfacing layer was fabricated to improve the properties of Q235 low carbon steel. For practical industry application, keyhole tungsten inter gas (K-TIG) welding was used to weld the surface-modified plates. The microstructure, elemental distribution, micro-hardness, and corrosion resistance of the surface-modified plates and the welded joints were analyzed. The corrosion tests of welded joints and surface-modified plates were carried out with the electrochemical method and hydrochloric acid immersion method, respectively, and surface morphology after corrosion was studied. The results show that the surface-modified plates and their welded joints were defect-free. The microstructure of the surfacing layer consisted of austenite, martensite, and ferrite; and the microstructure of the weld consisted mainly of martensite. The hardness and corrosion resistance of the surfacing layer was superior to that that of low carbon steel. The micro-hardness of the weld is higher than that of the stainless steel surfacing layer and the base material. The corrosion resistance of the surfacing layer is the best, and the corrosion resistance of the welding seam is better than that of the base material. Full article

The microstructure evolution, elements diffusion and fracture behavior of the Stellite 6 weld overlay, deposited on 10Cr9Mo1VNbN (F91) steel by the tungsten inert gas (TIG) cladding process, were investigated after long-time service. Obvious diffusion of Fe occurred from the steel and fusion zone to the Stellite overlay, resulting in the microstructure evolution and hardness increase in the coating, where hard Co–Fe phases, σ phases (Fe–Cr metallic compounds) and Cr-rich carbides (Cr_18.93Fe_4.07C₆) were formed. Besides, the width of the light zone, combined with the fusion zone and diffusion zone, increased significantly to a maximum value of 2.5 mm. The fracture of the Stellite coating samples mainly occurred in the light zone, which was caused by the formation and growth of circumferential crack and radial crack under high temperature and pressure conditions. Moreover, the micro-hardness values in the light zone increased to the maximum (470–680 HV) due to the formation and growth of brittle Co–Fe phases. The formation of these cracks might be caused by formed brittle phases and changes of micro-hardness during service. Full article

This work provides a comprehensive investigation of multi-walled carbon nanotubes (MWCNTs) inducement in weldment and their apparent effect on the microstructure, %elongation and ultimate fracture behavior of Al-Mg-Si alloy referring modified tungsten inert gas (TIG) welding joints. Serious experimental work is carried out at 1 wt%, 1.5 wt%, and 2 wt% of MWCNTs to provide a gradually increasing heterogeneous nucleation. The behavior of grain morphology showed the pure field of epitaxial growth without MWCNTs, and the forestry type morphology for 1 wt% MWCNTs at low welding currents (160 A), though there was a noticeable conversion into equiaxed (EQZ) grains filled with inter-dendritic particles at high welding currents (180 A and 200 A) for 1.5 wt% and 2 wt% of MWCNTs. Moreover, the formation of a cellular type network above the fusion line predominated initially at all parameters. Conversely, fine EQZ grains were formed as they moved upward into the welded zone (WZ) explicitly at a high heat input. A conceptual pictorial model is presented in the study which summarized the behavior of morphological changes at the utilized parameters. The welded joints have demonstrated an increasing trend of strength and %elongation in contrast to joints without added MWCNTs. Comparative results have shown an exceptional increment of 71 to 76% and 67 to 75% of elongation up to ultimate tensile strength (UTS), and a fracture point that was clinched for 1 wt% and 1.5 wt% MWCNTs at 180A. From macro to micro-examination of the fracture surfaces, pure ductile modes constituting elliptical cup and cone type isotropic flow was evident in all specimens. Detailed confirmation of the pull-out fracture mode of MWCNTs has highlighted in the scanning electron microscope (SEM) images that intimated a methodical contribution in load-transfer from matrix to the fiber under axial load. Overall, a concise en-route for MWCNTs inducement is well-appointed through tube fillers along with an activating facilitator (TiO₂) in contrast to stereotype fillers for improved behavior termed as modified TIG welding joint process in study. Full article

The usage of AISI/SAE 304L austenitic and 420 martensitic stainless steels is receiving greater interest especially in the defence and navy industries. 304L stainless steels exhibit excellent resistance to oxidizing media, while martensitic 420 alloy provides high strength values besides satisfactory corrosion properties at ambient atmospheres. In this work; 420 quality martensitic stainless steel is TIG (Tungsten Inert Gas) welded with 304L quality low carbon austenitic stainless steel plates. As filler metal dominantly determines the weld metals chemical compositions and final microstructures, 3 different TIG welding rods of ER312, ER316L ve ER2209 are used in welding operations in order to obtain 3 discrete weld metal contents under high purity argon shielding gas. Microstructural inspection, microhardness survey and Charpy V-notch impact tests are applied to all joints after welding operations. The specimen welded by ER2209 TIG welding rod executed the highest impact test results besides exhibiting the lowest micro-hardness profiles at heat affected zones and weld metals. All of the welded specimens weld region hardness profiles were determined to be lower than unwelded 420 martensitic stainless steel base metal. Full article