Weld Zone Research Articles

Reconstruction of the deformation history of an active fault: implications from the Atera Fault, Central Japan

Atera Fault clay gouges were collected for age dating near Kawaue, Nakatsugawa City, Central Japan, and the results integrated within its complex geological history. The results form an internally consistent data set constrained by extensive geochronological data (AFTA, ZFTA, CHIME) and support the application of gouge dating in constraining timing of brittle deformation in Central Japan. The Atera illite age data complete recently obtained limited illite fault gouge age data from underground exposure in the Toki Granite; the new illite age data are identical within error. The age of the heterogenous welded tuff breccia zone (Atera 1) ranges from 40.6 ± 1.0 Ma to 60.0 ± 1.4 Ma, whereas ages of the fault core gouge sample (Atera 2) range from 41.8 ± 1.0 Ma to 52.7 ± 1.2 Ma. The finest < 0.1 µm fraction of the fault breccia and fault core gouge yield ages around 41 Ma, identical within error. The new illite age data indicate brittle faulting and a following geothermal event occurring in the Paleogene–Eocene, similar to the nearby Toki Granite area and confirm they were both synchronous with a post-intrusive pluton exhumation. The Atera Fault illite age data provide additional insights into an integrated, regional-scale record of the tectonic displacement of Central Japan and might be influenced by large-scale tectonic processes such as the Emperor sea mount kink around 55 to 46 Ma with fault initiation around 50 Ma and brittle fault cessation or reactivation around 40 Ma in the Eocene.Graphical

Effect of Nitrogen‐Added Shielding Gas on Microstructure Evolution of Welded Joints by Gas Tungsten Arc Welding Process in Duplex Stainless Steel 2205

Duplex stainless steels (DSS), due to their high corrosion resistance, primarily attributed to their austenite‐ferrite duplex microstructure, are widely used in industrial sector such as petrolchimical and gas natural industries. Maintaining this microstructure is crucial during manufacturing processes, including welding which presents the challenge of minimizing ferritization in the heat‐affected zone (HAZ) or weld zone (WZ), as it can significantly reduce their corrosion resistance. This work aims to describe the influence of nitrogen gas in the Ar–N2 shielding atmosphere when depositing beads on 2205 DSS plates, using a gas tungsten arc welding (GTAW) process. It is observed that at low nitrogen load (98%Ar–2%N2), the austenite content reaches 49% in WZ and 29% in HAZ. When the nitrogen percentage is increased (50%Ar–50%N2), the austenite content rises to 67% and 37%, respectively. The joint is evaluated macro‐ and microstructurally to observe the atmosphere impact on weld bead geometry and microstructural development. Additionally, hardness is assessed throughout the weld bead. The work demonstrates that, with a 50%Ar–50%N2 shielding gas mixture, it is possible to limit the formation of ferrite in the WZ and HAZ of DSS during the welding process, without altering the microhardness trend of the welded joint.

Prediction of extreme temperatures in weld zone of friction stir welding

Prediction of extreme temperatures in weld zone of friction stir welding

Microstructure and failure behavior of ultrasonic-assisted resistance spot welded AA6061/Ti6Al4V joints

The ultrasonic-assisted resistance spot welding (UaRSW) technique was applied to join AA6061 aluminum alloy to Ti6Al4V titanium alloy, the microstructure and mechanical performance of the joints with and without ultrasonic were investigated. Ultrasonic increased the maximum load by 43%, doubled the displacement at fracture and significantly enhanced energy absorption capacity. The solid phase transformation zone formed in Ti6Al4V, and its microstructure was lath martensite. Due to the welding defects and coarse columnar dendrite, conventional spot welded joints fractured by interfacial failure mode with poor performance. Ultrasonic promoted the diffusion of AA6061, removed the welding defects, generated consistent equiaxed grains in weld zone, and the joints fractured in AA6061 base metal by button pull-out mode result from the higher bonding strength.

An innovative pulsed current arc welding technology for armor steel: Processes, microstructure, and mechanical properties

This study presents a novel pulsed current arc welding technology, specifically pulsed current gas tungsten arc welding (PC-GTAW), single and double pulse gas metal arc welding (SP/DP-GMAW), and dual process welding (D-process). This study aims to investigate the effectiveness of these welding techniques for armor steel weldments. This research focused on investigating the welding processes, resulting microstructures, and mechanical properties of welded joints. Based on the macrography analysis, it was determined that the weldments exhibit no signs of porosity, inclusions, or inadequate penetration. This finding substantiates the optimum settings for the weldment production process. The weldment optical microstructure, fusion, and heat-affected zone were examined in the weld interface. The microstructural properties of the FZ include δ-ferrite, austenite, bainite, and acicular martensite. The HAZ has a bainite-untempered martensite microstructure. The chemical composition and variations across the weldment (base, weld and HAZ) were identified. The grain borders contained greater quantities of Cr, Ni, Mn, Si, and Mo than those of the grain cores. EBSD revealed average weld zone grain sizes of 17.7 µm, 32.6 µm, 30.8 µm, and 24.6 µm for PC-GTAW, SP-GMAW, DP-GMAW, and D-Process, respectively.Furthermore, the hardness measurements showed a progressive transition across different regions. Additionally, the D-Process-fabricated material exhibited a maximum ultimate tensile strength of 872 MPa and an elongation of 4%. The mechanical properties exhibited by this new process variant exceed those of other weldments, indicating its potential for fabricating armor steel. The impact toughness demonstrated superior performance in all the weldments. Within this context, the new use of pulsed current advanced welding methods has shown the ability to generate welded parts of exceptional quality.

Enhancing friction stir welding efficiency through rotational speed adjustment: a microstructural and mechanical analysis of Al-Cu alloy

Friction stir welding (FSW) has gained prominence in the aerospace and automotive industries due to its ability to produce high-strength and defect-free welds in aluminum alloys. The present investigation focuses on the impact of different tool rotational speeds (such as 700 rpm, 900 rpm, 1100 rpm and 1300 rpm), on the microstructure and mechanical characteristics of friction stir welded Al-Cu alloys. With the use of optical microscopy, scanning electron microscopy (SEM), x-ray diffraction (XRD), and evaluations of hardness, tensile characteristics, and fracture behavior, a thorough analysis was carried out. The weld nugget zone contained significant changes in grain size and shape as a function of rotational speed, as shown by microstructural analysis. The grain structure gradually became more refined when the rotating speed was raised from 900 to 1500 rpm. According to SEM observations, at faster speeds, the weld zone showed fewer defects per unit area and better bonding properties, which might be attributed to better material flow and plastic deformation. The effect was further clarified by XRD analysis, which showed differences in phase composition with varying rotating speeds. Evaluations of the mechanical properties showed a significant relationship between rotating speed and the mechanical performance of the welds. Hardness measurements showed that as rotating speed increased, hardness levels gradually increased. Welds made at faster rotational speeds had better elongation and tensile qualities, according to tensile tests. Additionally, fracture behavior study revealed that higher rotational speed welds displayed a more ductile fracture mode, indicating increased toughness.

SPIF of micro-FSWed dissimilar AlMgSi alloy: formability analysis

ABSTRACT Tailor-welded blanks (TWB) facilitate strategic material placement, ensuring desired materials are positioned appropriately, while single-point incremental forming (SPIF) enables versatile shape manufacturing with minimal tooling. Despite both methods offering customization benefits, their combined potential remains largely unexplored. This study utilized friction stir welding to create one-millimeter-thick similar and tailor-welded blanks from AA6061 and AA6003. The weld quality was ensured through metallurgical analysis and mechanical testing. SPIF of welded blanks exhibited formability comparable to parent materials, free from weld-line movement or fractures in the weld zone during forming. However, TWBs demonstrated formability between their constituting parent materials. Fractures occurred in almost all blanks due to bi-axial stretching in the corner of the D-shape. Investigation into the effect of tool size and geometry revealed that too small tool diameters induced localized deformation, contributing to failure. While flat-bottomed tools exhibited higher material thinning than hemispherical tools.

A novel approach to suppression of reverted austenite in aerospace grade thick maraging steel weldments using the turbo-TIG welding process

This research examines aerospace grade-maraging steel weldments produced by the novel Turbo-TIG welding technique. The vital challenge in welding maraging steel is the development of reverted austenite in the weld region and HAZ. This reverted austenite degrades the mechanical characteristics of weldments. MDN 250 maraging steel with a 12 mm thick plate was welded at a high speed of 300 mm/min with consistent quality using the Turbo-TIG welding technique. The objective of the present work is to suppress the reverted austenite in the 12 mm thick plate of MDN 250 using the Turbo-TIG welding technique. Three different postweld heat treatments were applied, namely, (i) aging heat treatment (AT), (ii) solutionizing + aging (ST), and (iii) homogenization + solutionizing + aging (HT). The microstructure and X-ray diffraction analysis of the weld zone under AT and ST conditions demonstrate the existence of reverted austenite in the grain boundary regions. The SEM/EDS analysis of the weld zone of welded, AT, and ST conditions indicated Ni, Mo, and Ti microsegregation from the center matrix to the grain boundary regions. In contrast, neither microsegregation nor austenite reversion occurred in the HT condition. The tensile test demonstrates a maximum strength of 1797 MPa (UTS) under HT conditions. Likewise, the microhardness of the HT conditions exhibits a higher hardness of 552 HV in the fusion zone. In light of the metallurgical and mechanical characteristics of the weld, the HT heat treatments provide better weld performance in the case of Turbo-TIG welding of maraging steel grade MDN 250.

Corrosion behavior and microstructure analysis of butt welds of Q690 high strength steel in simulated marine environment

Steel components that have served in the marine environment for extended periods often face challenges in preventing surface damage caused by corrosion protection measures. These challenges can ultimately diminish the expected service life of structures. To investigate the corrosion behavior and time-varying effects in butt welds of Q690 high strength steel in the ocean splash zone, a macroscopic morphology analysis was conducted using various corrosion times involving indoor saltwater immersion and hot-humid cycling accelerated corrosion. Quantitative analysis of corrosion pits' size and distribution range was performed in both the weld zone (WZ) and heat-affected zone (HAZ) to establish a relationship between roughness parameters and corrosion time. Experimental results were compared with corrosion parameters of regular steel. The findings reveal a gradual reduction in metallic luster with increasing corrosion time on specimen surfaces. Moreover, a greater accumulation of corrosion products is observed in the butt weld region, leading to progressive corrosion damage. High strength steel (HSS) exhibits superior corrosion resistance compared to ordinary steel. However, the corrosion damage of HSS weld joints gradually approaches that of ordinary steel in the later stage of corrosion. Microscopic scanning indicates that the accumulated corrosion layer effectively impedes the penetration of corrosive media into the matrix's interior, while the surface microstructure transitions from pitting to corrosion pits. These research findings significantly contribute to assessing the performance and analyzing the reliability of high strength steel in marine environments.

Evaluation of True Bonding Strength for Adhesive Bonded Carbon Fiber-Reinforced Plastics.

Carbon fiber-reinforced thermoplastics (CFRTPs) have attracted attention in aerospace because of their superior specific strength and stiffness. It can be assembled by adhesive bonding; however, the existing evaluation of bonding strength is inadequate. For example, in a single-lap shear test, the weld zone fails in a combined stress state because of the bending moment. Therefore, the strength obtained experimentally is only the apparent strength. The true bonding strength was obtained via numerical analysis by outputting the local stress state at the initiation point of failure. In this study, the apparent and true bonding strengths were compared with respect to three types of strength evaluation tests to comprehensively evaluate bonding strength. Consequently, the single-lap shear test underestimates the apparent bonding strength by less than 14% of the true bonding strength. This indicates that care should be taken when determining the adhesion properties for use in numerical analyses based on experimental results. We also discussed the thickness dependence of the adhesive on the stress state and found that the developed shear test by compression reduced the discrepancy between apparent and true strength compared with the single-lap shear test and reduced the thickness dependence compared with the flatwise tensile test.

Effect of welding speed on microstructure, nano-mechanical and nano-tribological characteristics of dissimilar friction stir welded AA6061-T6 and AZ31 alloy

The microstructural, tribological, and mechanical performance of friction-stir welded AA6061-T6 and AZ31 alloys were investigated using electron back scattered diffraction, scanning electron microscope, X-ray diffraction, and electron dispersed spectroscopy methods. The non-destructive X-ray microcomputed tomography test was used to analyse weld porosity. The distribution of volumetric and surface flaws (pores) was found to be confined across the weldment. Using a novel atomic force microscopy method, the nano-tribological characteristics of the base metal and localized regions of welded sample were studied for the first time. The significant difference in wear and friction behaviour was observed in all weld zones and base metal of magnesium side, which was correlated with the hardness of these regions. AFM results showed strong variation in tribological properties in correlation with the hardness trends of different weld zones, i.e. higher hardness leads to low wear. In weldments, intermetallic compounds such as Al12Mg17 and Al3Mg2 were produced, resulting in nanohardness differences as measured by the nanoindentation test. The joint efficiency of 65%, 84%, and 91% were obtained at welding speeds of 16 mm/min, 20 mm/min, and 25 mm/min, respectively.

Analyzing microstructural, residual stress, and mechanical characteristics in dissimilar welds of Inconel 59 and AISI 904L through double-pulsed gas metal arc welding

In this research, dissimilar welding of the nickel-based superalloy Inconel 59 and austenitic stainless steel AISI 904L steel was successfully done with double-pulsed gas metal arc welding (DP-GMAW) using the filler ERNiCrMo-13. Macroscopic analysis showed a defect-free weld with an aspect ratio of 2.4, attributed to the efficient heat delivery (0.642 kJ/mm) in DP-GMAW. The microstructure of the weld joint was examined through both optical microscopy and scanning electron microscopy. Examination of the microstructure of the weld interface exposed grain coarsening near the heat-affected zone on the AISI 904L side. In contrast, the weld fusion zone contained fine equiaxed dendrites. Microsegregation and alloying element migration across the entire weld area were assessed through energy dispersive X-ray spectroscopy point analysis and line mapping, revealing controlled microsegregation across the region. X-ray diffraction (XRD) analysis was used to ascertain the average grain size (38.41 nm) and secondary phase composition. The XRD-cosα method was used to assess the residual stress of the weld joint, revealing tensile residual stress in the weld zone and compressive residual stress in other regions. Tensile, Charpy impact, and Vickers hardness tests were conducted in the study to evaluate the strength, toughness, and hardness of a dissimilar weld. The impact of two cryogenic treatments, namely shallow and deep, on tensile and toughness characteristics was investigated in this study. The cryogenic treatments significantly enhanced the mechanical properties of weld samples compared to their as-welded condition, leading to an 11.5% increase in tensile strength and a 10% improvement in toughness.

Formation mechanism, microstructure and mechanical properties in current-introduced solid-state welding of dissimilar zirconium alloy

The cladding tube (Zr-Nb alloy) and the end plug (Zr-Sn alloy) were successfully joined using current-introduced solid-state welding. During the welding process, the metals undergo severe plastic deformation and were joined by dynamic recrystallization. With the increase of the forging force, the blasting force of the joint changes little. The joint exhibited a blasting force ranging from 8086 to 9037 N, and the fracture occurred in the cladding tube, away from the weld zone. The blasting fracture mode of joint is ductile fracture.

Full-field eigenstrain reconstruction for the investigation of residual stresses in finite length weldments

The reconstruction of welding residual stresses has been performed based on the assumption of continuous processing conditions, owing to the limitations of reconstruction methods. This assumption prevents the attainment of a comprehensive understanding of mechanical deformations in the entire weld zone. The voxel-based eigenstrain (inherent strain) reconstruction method emerges as an appropriate approach for the full-field reconstruction of residual stresses in finite length weldments without such assumption. The innovative reconstruction capability of this advanced method is presented in this study, aiming to comprehend all components of residual stresses and eigenstrains in finite length weldments with discontinuous processing properties using only a single component of experimental data belonging to a limited portion of the specimen. Numerical experiments were conducted to develop the tools. These tools were validated using a case study employing experimental data obtained through contact profilometry measurements from the surface of discharge machine cutting (minimally disturbing cutting) in a bead-on-plate weldment of Inconel alloy 740H designed for ultra-supercritical power generation. The reconstructed two components of normal residual stresses that do not align with the available experimental data were validated by independent neutron diffraction strain scanning quantifications. Furthermore, the reconstruction of residual stresses in the intact component prior to cutting was carried out using the eigenstrains associated with the post-cut state of the weldment.

Effect of rare Y-microalloyed Al–Mg filler materials on the microstructure and tensile properties of laser welded Al–Mg–Si alloys

The Al–Mg filler metals containing various amounts of yttrium (Y) were obtained and used to study the effect of the Y element on the microstructure and tensile properties of laser welded Al–Mg–Si alloys. The results revealed that compared with the unmodified welded joints, 0.1 wt%Y addition cannot effectively refine the grains. However, the 0.1 wt%Y addition effectively decreased the rich-Fe phases size and transformed the bulk β-AlFeMnSi phases into the fine granular AlFeMnSiY phases. Due to the precipitation strengthening, the welded joints with 0.1 wt%Y exhibited excellent mechanical properties, the highest tensile strength and elongation increased by 53.42 MPa and 5.58 %, respectively. As the Y content further increased, a significant grain refinement was observed in the weld zone. However, due to the small growth restriction factor of Y in aluminum alloys, the degree of grain refinement was limited. When 0.3 wt% Y was added, the grain size of the weld was the smallest, which was only reduced by 7.7 μm compared to the unmodified weld and similar to the weld with 0.5 wt%Y addition. Furthermore, the increase in solidification temperature range led to the growth of the second phase, as well as an increase in the number of coarse rich-Fe and Mg2Si phases. These combined reasons prevent further improvement of tensile properties of the welded joints.

Toward defect-less and minimized work-hardening loss implementation of Al alloy/high-purity Cu dissimilar lap joints by refill friction stir spot welding for battery tab-to-busbar applications

The refill-friction stir spot welding (RFSSW) process on the Al5052–H32 alloy joined with high-purity Cu film resulted in notable changes in the work-hardened Al alloy. The stirring action caused dynamic recrystallization in the weld zone, leading to the loss of work-hardening. Surprisingly, the plot of grain size-hardness in Al alloy after RFSSW did not follow the Hall-Petch relationship. Obtained through combined analysis with a transmission electron microscope, X-ray diffraction, and thermodynamic calculation, at the interface of Al and Cu, diffusion in nanoscale and microscale between the metals induced the formation of secondary phases (e.g., CuxAly intermetallic compounds, θ′ or θ'' phases), positively contributing to increased mechanical properties. The near-surface region in contact with the tool experienced significant compressive stresses, resulting in maximized compressive residual stresses. This, in turn, sustained or even enhanced the initial hardness of the material. Our study systematically investigates whether creating a lap joint with Cu in work-hardened Al alloy with RFSSW can yield a robust joint without defects in Al and without an overall loss of work-hardening.

High-temperature dynamic corrosion mechanisms of austenitic stainless and carbon steels in nitrates for concentrating solar power

Abstract: In this paper, to simulate the dynamic corrosion mechanisms of metals exposed to a high-temperature molten salt mixture of NaNO3–KNO3, the experimental samples made of commonly used stainless steel alloys such as 304 (with/without welds) and Q275 were suspended, along with stirring blades, in a specially designed stirred kettle to obtain their corrosion characteristics. For the experimental samples, the Q275 surface exhibited significant quantities of Fe3O4 and Fe2O3, while 304 generated FeCr2O4, Cr2O3, and MgFe2O4 with protective effects. The microstructure of the welding zone in 304 exhibited considerable disparities compared to that of the base material, consequently leading to augmented susceptibility towards localized corrosion. The uneven distribution of chromium in the welding zone resulted in intergranular corrosion and alterations in the crystal structure. Moreover, experimental studies have demonstrated that NO3- in the molten salt undergoes decomposition to generate oxygen ions, which contribute to the corrosion reaction. Notably, under all test conditions, the corrosion rate of samples exhibited the following ranking: 304 (without welds) < 304 (with welds) < Q275.

Effect of Filler Wires on Welding Strength and Microstructural Changes of Inconel 718 and AISI 316L Dissimilar Weldments

In this research, the effect of fillers wires on weldability, welding strength and structural changes of dissimilar welds of Inconel 718 and AISI 316L are studied. Pulse arc mode in TIG welding with multiple passes were used to join V-groove configuration with 1.6 mm filler diameter. Constant welding parameters were used for both the weldments to study the effect of alloying elements of filler wires. Tensile properties were evaluated by conducting tensile test on universal testing machine as per ASTM E/8 standards. To reveal the structural changes at various zones of weldment, optical microscope was utilized. The dissimilar metals were joined successfully using two-filler wires without any internal defects. The highest tensile strength of 553 MPa was observed in Hastelloy filler weldment when compared with ERNiCrMo-4 filler weldment (530 MPa). Also, the better yield strength properties were observed in Hastelloy filler weldment. Well defined with clear grain boundaries were observed in both the filler weldments. Due to the pulsed arc mode, segregation of alloying elements was reduced.

Process simulation and development for laser beam welding with rotating bifocal optics

Laser welding has been an established technology in industrial production. Nevertheless, there are many unsolved problems with cracks and pores when welding certain materials. New process or exposure strategies are therefore being developed to enable a controlled temperature field within the welding zone and thus deliver better welding results.The aim of this study is to investigate a new type of processing optic that uses bifocal optics to split the laser beam into two partial beams and a fast rotation of these two partial beams. Optimum welding parameters for stainless steel were determined while varying the rotational speed and laser power. the same time, simulations were created with the FLOW 3D software, which agree very well with the experimental results.

Analysis of Material Hardening Effect on the SCC Creep Characteristics Around the Crack Tip in the Welding Zone

Analysis of Material Hardening Effect on the SCC Creep Characteristics Around the Crack Tip in the Welding Zone