Weld Zone Research Articles

Fatigue crack propagation characteristics of aluminum/steel laser-metal inert gas fusion-brazed joints in different micro-zones

Research on fatigue damage of aluminum/steel dissimilar joints is critical to ensure the reliability of multi-material lightweight structures. In this study, the fatigue crack propagation (FCP) characteristics of the interface, weld, and heat-affected zone (HAZ) of aluminum/steel laser-metal inert gas (MIG) fusion-brazed joints were investigated. Additionally, the influencing role of the microstructure of different micro-zones on the FCP behaviors was discussed. Single-edge notched tensile (SENT) specimens of the interface region exhibited a higher crack growth rate and crack threshold than SENT-weld and SENT- HAZ specimens due to the highly hard and brittle nature of the intermetallic compounds (IMC) at the aluminum/steel interface. Moreover, the fatigue fracture surface of SENT-interface specimens showed a brittle fracture pattern without fatigue striation characteristics, which was different from aluminum/steel solid-state and traditional aluminum alloy welded joints. Electron backscatter diffraction (EBSD) analysis results revealed that the synergistic effects of grain size, sub-grain boundaries, and micro-performance all contributed to the crack deflection of SENT-weld at a large angle to the HAZ, thereby resulting in more optimized crack resistance in the weld zone.

Effect of continuous dynamic-recrystallisation on high-property multilayer Cu foils joint by friction-stir-welding

In this experiment, friction-stir-welding was proposed to research the flexible connection of multilayer Cu foils. It studies the correlation between hardness, conductivity, and continuous dynamic-recrystallisation. New grains of continuous dynamic-recrystallisation have a correlation between the dislocation density and the grain size, such that a lower dislocation density corresponds to a higher grain size and vice versa. It is shown that after friction-stir-welding of multilayer Cu foils, the hardness increases and the conductivity decreases due to the combined effect of fine grain strengthening and dislocation strengthening for new grains of continuous dynamic-recrystallisation of the weld zone. However, the hardness gradually decreases and conductivity gradually increases within the weld zone with continuous dynamic-recrystallisation degree.

Microstructure and residual stress distribution of electron beam-welded joints of a 50 mm-thick TA15 titanium alloy plate

Abstract Vacuum electron beam welding was applied to a 50 mm-thick TA15 titanium alloy plate. Microstructure observation and microhardness testing were performed. Meanwhile, the residual stress on the surface at different distances from the weld centre was measured via the hole drilling method. A finite element model for electron beam welding of the TA15 titanium alloy plate was constructed on commercial finite element software. Experimental results showed that the microstructure of the weld zone consisted of a basket martensitic phase. The highest microhardness in the weld zone was 409 HV, and the microhardness of the base metal was the lowest. The maximum gradient change area was located at the HAZ near the base metal. The peak value of longitudinal residual stress from the simulation was 880 MPa, which was in the weld metal. The sharp change area of longitudinal residual stress gradient was located in the base metal near HAZ.

Insight into the corrosion susceptibility and failure mechanism of Cu-Ni alloy pipeline welded joints in simulated marine environment

In this work, the corrosion behavior of Cu-Ni alloy pipeline welded joints is investigated in a simulated marine environment solution with coexisting chloride ions (Cl−) and sulfide ions (S2−). Microstructural observation, chemical component analysis, electrochemical measurements, scanning kelvin probe (SKP) and the finite element method (FEM) were adopted to probe the corrosion failure mechanism. The results showed that the welded joints at base metal (BM), heat affected zone (HAZ) and weld zone (WZ) exhibit various microstructures and reveal pitting and intergranular corrosion, moreover, the WZ appears inter-dendrite corrosion. WZ exhibits a higher corrosion sensitivity with the highest corrosion current density of about 1.23 × 10−5 A·cm−2. The defects in passive film and the thickness and density of corrosion product film differ for the three zones resulting in the protective effect of WZ being the poorest. BM with the thickest and densest corrosion product film effectively prevents the infiltration of corrosive ions (HS−, Cl−), meanwhile, the lowest defect concentration of the passive film of BM further protects the substrate. The transition of WZ in the WZ-HAZ galvanic couple from cathode to anode aggravates the corrosion of WZ.

Comparison of V groove design on mechanical performance and fracture behaviour in TIG welding of 5754-H111 aluminium alloy

The aim of this study is to enhance the performance and effectiveness of welding 5mm thick plates with different groove designs and investigate their post-effects on material properties. Specifically, the study compares single V and double V butt joints of 5mm thick AA5754-H111 strain-hardened aluminium alloy using Tungsten Inert Gas (TIG) welding with ER5356 (Al-Mg) filler rod. Two types of weld grooves, single V groove and double V groove were utilized to examine the microstructure and character of the weld and to study the effect of heat distribution. The average Vickers hardness values were observed to be 78.2HV in the double V groove of weld zone compared to the 76.6HV in single V groove weld zone. The tensile strength of single V and double V groove were 210 and 207 MPA respectively. The results showed that the failure location of all weld samples was in the fusion zone (FZ) and exhibited brittle fracture. The microstructure of the weld fusion zone revealed the presence of porosity in various sizes, which was also observed in the fractography images of tensile failed samples. Moreover, the microstructure studies exhibited clear variations in the fusion, intersection, and heat-affected zones. The formation of particles was found to differ in the weld fusion zone at various locations due to changes in the V groove welding method.

Simulating the structure-property relationship in weld zones

Simulating the structure-property relationship in weld zones

Effects of magnetic field and post-weld heat treatment on microstructure and properties of laser welded joints of 22MnB5-TRIP590 steel

Laser welding without and with an auxiliary magnetic field (B = 30 mT) is performed on 22MnB5-TRIP590 steel. Subsequently, post-weld heat treatment, involving quenching at 800 °C followed by tempering at 200 °C, is carried out on the welded joints prepared by these two welding processes (B = 0 mT, B = 30 mT). This study examines the improvement of microstructures and mechanical properties of the welded joints by applying the magnetic field (B = 30 mT). Furthermore, this research investigates whether these enhanced characteristics of the welded joints persist after post-weld heat treatment. When the magnetic field is applied, the overall width of the welded joint is significantly reduced, and the microstructure of the weld is changed mainly from proeutectoid ferrite, granular bainite, and upper bainite to lath martensite and lower bainite. Furthermore, the grains in the coarse grain zone are refined, and the plasticity and overall hardness of the welded joint are considerably improved. After post-weld heat treatment, the weld and coarse grain zone of both welded joints (B = 0 mT, B = 30 mT) are mainly tempered martensite, and the tensile strength and overall hardness are significantly improved compared to those without post-weld heat treatment. Although the plasticity of two welded joints is lower than that of two unheated-treated welded joints, the fracture positions are all at the base metal and are both ductile fractures. The improved characteristics, such as optimized macro-morphology, refined grain morphology, improved plasticity, welded joint efficiency, and weld hardness of magnetic field-assisted laser welded joint, are all retained after post-weld heat treatment. A thorough comparison reveals that the magnetic field-assisted laser welded joint with post-weld heat treatment has better comprehensive mechanical properties.

Improving the quality of the ultrasonic welded thermoset-based composites using laser surface treatment

In this article, ultrasonic welding of glass fiber-reinforced thermosetting polymers which were surface-treated by laser engraving, is investigated. Composite samples were prepared by hand lay-up method. In the next step, surface treatment of the composite samples was performed by means of a high-power laser confirming two grooved and circular patterns. Polymethylmethacrylate and polypropylene as the amorphous and semicrystalline thermoplastic intermediate layers were incorporated to create a joining between the two thermoset parts. Besides, the welding time was considered in the three different levels. In order to investigate the microstructure of the welding zone, scanning electron microscopy analysis were accomplished. Besides, lap-shear tests were performed so as to evaluate the mechanical performances of the welded parts. Morphological studies indicated that in the surface-treated samples, the penetration of the intermediate material into the welded parts is much higher than neat samples and this leads to the superior interaction between the coupling layer and the surface-treated parts. Confirming the morphological outcomes, the results of the lap-shear tests specified that the application of surface treatment using laser engraving has increased the laps-shear strength almost 5.5 times compared to the samples without preparation.

Unlocking the effect of interfacial microstructure and Desulfovibrio vulgaris on corrosion characteristics in copper-nickel alloy welded joint

The microbiologically influenced corrosion (MIC) behavior of the copper-nickel (Cu-Ni) alloy welded joint induced by Desulfovibrio vulgaris was investigated. Distinct gradient changes in MIC behavior were observed in different regions, with the heat-affected zone (HAZ) consistently exhibiting higher localized corrosion sensitivity. Specifically, the asymmetric corrosion of HAZ was attributed to the galvanic effect between HAZ and welding zone (WZ). On a submicroscopic scale, the WZ acted as a cathode, mitigating corrosion in the later stages of Desulfovibrio vulgaris incubation. Additionally, the deep corrosion propagation at the HAZ/WZ interface was caused by the combined action of galvanic effect and Desulfovibrio vulgaris.

Local mechanical properties of dissimilar metal TIG welded joints of CoCrFeMnNi high entropy alloy and AISI 304 austenitic steel

Multiple principal element alloys encompass the well-known high entropy alloys (HEA). The alloy system represents a new class of materials consisting of at least three alloying elements, each containing 5 to 35 at.%. Thus, this alloying concept differs fundamentally from conventional materials such as steel or nickel alloys. For this purpose, the alloying elements are specifically selected, the microstructures are adjusted in a single-phase and, in some cases, multi-phase manner. In particular, conflicting goals, such as the trade-off between strength and ductility in conventional steels, are overcome. However, in the last 20 years, the focus has been on material synthesis. With the increase in available material quantities, the focus is now on processing issues such as joining and welding processes. The weldability of HEAs has received very little attention so far. The experience with dissimilar metal welds is completely lacking but is essential for the application of these materials in combination with conventional materials. The present study presents comprehensive experimental results on the weldability of an equimolar CoCrFeMnNi-HEA in cold-rolled and heat-treated condition, which was joined by tungsten inert gas welding to an austenitic steel AISI 304. The mechanical properties of the dissimilar metal welds were characterized by cross-weld tensile samples, whereas the local deformation in the weld of the different welding zones was measured by digital image correlation. In accordance with the respective initial HEA condition (cold-rolled vs. heat-treated), the local strain behavior was divergent and influenced the global mechanical properties of both DMW types. Nonetheless, the experiments provided proof in principle of the weldability for dissimilar joints of the CoCrFeMnNi-HEA welded to conventional materials like austenitic stainless steels ensuring a corresponding capability for mechanical loading. This allows further considerations on the application of these innovative materials.

Formation and strengthening mechanism of equiaxial cellular grain zone in AA2195-T8 Al–Cu–Li alloy twin-wire P-VPPA welded joint with Ti–Zr microalloying

A novel method involving twin-wire pulsed VPPA (P-VPPA) welding was combined with Ti–Zr microalloying to improve the mechanical properties of AA2195-T8 Al–Cu–Li alloy variable polarity plasma arc (VPPA) welded joints. This method aimed to increase the width of the equiaxial cellular grain zone (ECZ) by adding higher content of Ti–Zr and reducing heat input. The microstructure evolution process was established to understand the formation and strengthening mechanism of the ECZ. The results showed that the strength of the ECZ was higher than that of the dendrite in the weld zone (WZ). The twin-wire VPPA welding led to the formation of a wider ECZ near the fusion zone (FZ). This ECZ was continuously distributed throughout the thickness direction of the welded joint. Combined with higher Ti–Zr microalloying, the maximum width of ECZ increased to 2.5 mm and extended to the WZ. Consequently, the proportion of cracks passing through the ECZ during tensile fracture increased from 27.6% to 88.7%. Moreover, the ultimate tensile strength (UTS) of the welded joint exhibited a notable improvement, rising from 328 MPa to 370 MPa, while the elongation also increased to 5%. The UTS of the welded joint achieved 66% of the base metal. Additionally, the average grain size in the ECZ was 14 μm. The formation of the ECZ was primarily attributed to the nucleation precursors of Al3(Ti, Zr) and β′ phase, as well as less welding heat input near the FZ. The widening of the ECZ was mainly due to the presence of more Al3(Ti, Zr) phases. Moreover, the grain boundary of the ECZ exhibited the distribution of Al–Cu eutectic, θ(Al2Cu), Ω, T2(Al6CuLi3), and ω(Al7Cu2Fe) phases, while a small amount of T1(Al2CuLi) phase precipitated within the grain. The strengthening mechanism of ECZ is the result of multiple strengthening effects, including the reduction of element segregation and microcracks, the precipitation of the T1 phase, and the fine grain strengthening.

Analysing suspected linear indications in narrow-gap welding of nuclear power plants via radiographic inspection

ABSTRACT In nuclear power plants, ensuring the integrity of main coolant line welding is vital. Radiographic testing often shows linear indications in these welds, posing challenges for quality assessment and requiring expensive reworking. To investigate the mechanism of the suspected linear indications observed in radiographic inspections of narrow-gap welding at nuclear power plants, the microstructure, microhardness, and porosity of welds showing such indications were investigated in this study using scanning electron microscopy and atomic probing methods, among others. The microvoid distribution in narrow-gap welds was characterised by porosity measurement. The results showed that the microstructure of the weld consists of an austenite matrix and δ-ferrite, with the latter distributed almost uniformly during welding. The average δ-ferrite content and microhardness were approximately 6.6% and 186 HV0.49N, respectively. The porosity of the welding zone with a suspected linear indication was approximately 0.06%, higher than the 0.03% observed in the zones without such indications. This difference is likely responsible for the linear indications detected in radiographic inspections. However, the results demonstrated that this difference does not affect the welding microhardness. The novelty of this study lies in explaining the role of porosity in causing suspected linear indications in narrow-gap welding in nuclear power plants.

Effects of carbon source starvation and riboflavin addition on selective corrosion of welded joint by Desulfovibrio vulgaris

This study systematically explores the impact of carbon source starvation (CCS) and the addition of riboflavin on the corrosion of X80 welded joints by Desulfovibrio vulgaris. The results showed that the Desulfovibrio vulgaris corrosion of the welded joint was apparently selective under the independent action of CCS or riboflavin addition, while the selectivity distinctly decreased under their combined action. More grain boundaries and higher proportion of the low-angle grain boundaries in the base metal and welding zone were the reasons for the selective corrosion. The attachment behavior of the Desulfovibrio vulgaris cells was responsible for the decreasing of the selectivity.

Three-dimensional peridynamic modeling of deformations and fractures in steel beam-column welded connections

The integrity of steel structures depends primarily on the strength of beam-column connections. The paper presents a new and novel three-dimensional (3D) peridynamic model to study the fracture behavior of steel beam-column welded connections. The mesh-free nature of the peridynamic method enables simulating the excessive deformation and fractures in steel elements. The 3D peridynamic model is validated by comparing its fracture and deformation results with experimental data from several beam-column welded connections. According to the proposed model, there are two conditions for the failure of steel beam-column welded connections as follows: 1) crack propagation in the steel elements (beam or column) or bonds’ breakage in the welding zone (welding defects); 2) sudden drop of the load value in the load–displacement curve. The study emphasizes its originality by presenting an efficient tool for researchers and engineers to examine fracture responses in steel beam-column welded connections under various conditions. The inclusion of different steel section profiles adds versatility to the study. The paper also explores the performance of new steel beam-column welded connection cases. Moreover, the paper examines the effects of welding defects in the fracture mechanism of steel beam-column welded connections. This study demonstrates that welding defects can determine the failure source and mechanism. Moreover, the load capacity of steel beam-column welded connections decreases due to the welding defects. This finding underscores the importance of welding quality in maintaining the structural integrity of these connections.

Study of Microstructure and Performance Evaluation of Zr-Sn-Nb Joints by Electron Beam Welding.

In this work, Zr-Sn-Nb alloy was joined by electron beam welding (EBW). A defect-free Zr-Sn-Nb joint with sound appearance was obtained. The grains in the weld zone (WZ) and heat-affected zone (HAZ) are significantly coarsened. The columnar grains with a maximum grain size of 0.5 mm are distributed in the upper region of the WZ, while the equiaxed grains are almost located in the bottom region of the WZ. The WZ is mainly composed of the dominant α-Zr, α'-Zr and a few β phases. The grain orientation of WZ and HAZ is uniform, indicating that no obvious preferred orientation existed. Coarse grains and fine acicular α' phases increase the strength of the joint, but reduce the plasticity and toughness of the joint. The tensile strengths of the joints at room temperature (RT) and 375 °C were 438 MPa and 313 MPa, respectively. The RT impact energy of the joint is 18.5 J, which is only 58.3% of the BM. The high purity of the EBW process and unsignificant grain orientation minimizes damage to the corrosion resistance of Zr-Sn-Nb alloy joints. The corrosion weight gain of the joint specimen and the BM specimen were 12.91 mg/dm2 and 12.64 mg/dm2, respectively, and the thicknesses of the cross-section corrosion layer were 12-15 μm and 9-12 μm, respectively.

Mechanical properties and corrosion resistance study of dissimilar metal thin sheet friction stir welded joints

This study employs friction stir welding (FSW) technology to achieve the butt welding of 2mm thick 1060 aluminum and T2 copper. The research investigates the macroscopic formation, tensile properties, microhardness, and electrochemical corrosion behavior of the welded joints. The results indicate that the welded joints exhibit excellent formation, with a tensile strength reaching 84.76% of that of the 1060 aluminum material. Well-formed welded joints can be obtained by controlling the rotation speed and welding speed within a certain range. However, the rotation speed has a more significant impact on the microhardness in the weld zone. The corrosion potential of T2 copper is higher than that of 1060 aluminum, forming a macroscopic galvanic couple between the two materials. The corrosion potential of the welded joint falls between that of T2 copper and 1060 aluminum.

Microstructural Characterization and Corrosion Behavior of Similar and Dissimilar Welded Advanced High-Strength Steels (AHSS) by Rotary Friction Welding.

Advanced high-strength steels (AHSSs) are designed for meeting strict requirements, especially in the automotive industry, as a means to directly influence the reduction in the carbon footprint. As rotary friction welding (RFW) has many important advantages over other welding technologies, it plays an important role in the automotive sector. On the above basis, in this work, combinations of the first (complex phase (CP)), second (TWIP (TW)), and third (quenched and partitioned (Q&P)) generations of similar and dissimilar high-alloyed advanced steels have been joined by the RFW process. Having a specific microstructure, rods of CP/CP, Q&P/Q&P, CP/TW, and Q&P/TW steels were welded by employing a homemade adaptation machine under fixed parameters. Microstructural characterization has allowed us to corroborate the metallic bonding of all the tested advanced steels and to identify the different zones formed after welding. Results indicate that the welding zone widens in the center of the workpiece, and under the current friction action, the intermixing region shows the redistribution of solute elements, mostly in the dissimilarly welded steels. Furthermore, because of their complex chemistry and the different mechanical properties of the used steels, dissimilarly welded steels present the most noticeable differences in hardness. The TWIP steel has the lower hardness values, whilst the CP and Q&P steels have the higher ones. As a direct effect of the viscoplastic behavior of the steels established by the thermomechanical processing, interlayers and oxidation products were identified, as well as some typical RFW defects. The electrochemical response of the welded steels has shown that the compositional and microstructural condition mostly affect the corrosion trend. This means that the dissimilarly welded steels are more susceptible to corrosion, especially at the TWIP-steel interface, which is attributed to the energy that is stored in the distorted microstructure of each steel plate as a consequence of the thermomechanical processing during RFW.

Application of Central Composite Design, Response Surface Methodology in Predicting the Thermal Expansion of Mild Steel Weldment

The compositional range of materials to be welded, the thickness of the base materials, and current type are the main determining variables in the choice of welding. However, thermal expansion in mild steel weldments occurs when the material expands or contracts when subjected to changes in temperature during welding or subsequent heating and cooling cycles. This expansion and contraction can lead to residual stresses, distortion, and even cracking in the weldment if not properly managed. Mild steel, like many other metals, expands when heated and contracts when cooled. One major challenge occurs when during welding, the high temperatures cause the metal to expand in the heat-affected zone (HAZ) and the weld zone itself, then as the weldment cools down, it contracts, but this contraction might not be uniform due to differences in cooling rates across the weldment. The present study aims to predict the thermal expansion of mild steel weldments in relation to the current, voltage and gas flow rate. The central composite design is used for the design of experiment of 20 experimental runs, while the Response Surface Methodology (RSM) was used for the analysis. The model used in the RSM is Quadratic, while the coefficient of determinant, R-Squared of 0.9642, Adj R-Squared, 0.9319, Pred R-Squared, 0.7133, Adeq Precision 22.307 were obtained. There was no outliner which showed that the model adequately predicted the response. The study establishes that thermal expansion of mild-steel weldment can be adequately predicted by applying expect system such as the Response Surface Methodology.

The influence of weld fluid flow on the formation mechanism of intermetallics and HfO2 precipitates in dissimilar electron beam welding of C-103 niobium alloy to nickel

In this research, the effect of weld fluid flow in molten pool on the formation and behavior of intermetallic compounds NbNi3 and Nb7Ni6 and HfO2 precipitates in dissimilar electron beam welding of niobium base alloy C-103 to nickel was investigated. It was observed that due to the large difference in the melting temperature of the base metals, nickel contributed 82% by volume and C-103 contributed 18% by volume in weld zone. In the weld zone and attached to the C-103 base metal, a thin and continuous intermetallic zone was formed, including the initial phase of NbNi3 and the eutectic structure of NbNi3+Nb7Ni6. In the areas after the continuous intermetallic layer in welding, the initial phase of NbNi3 and the eutectic structure of NbNi3+γ-Ni are formed. During welding, HfO2 particles in the C-103 base metal enter the molten pool due to the weld fluid flow and remain as white precipitates in the welding zone and close to C-103. In addition to these precipitates, nanometer precipitates of HfO2 are also observed in the weld, which are formed in-situ in the weld due to the reaction of hafnium with dissolved oxygen in the melt. In the central zone of the weld, continuous band-shaped intermetallic layers can be observed which have been removed from the wall of C-103 due to the fluid flow of the molten pool and moved towards the central zone of the weld. These layers act as nucleus in the center of the molten pool and solidification occurs from their surface. At first, solidification begins with the planar growth of the initial phase of NbNi3, and then cellular and columnar dendritic growth occurs. At the end of solidification, the eutectic structure of NbNi3+γ-Ni forms between cells and dendritic branches. Due to the presence of intermetallic compounds NbNi3 and Nb7Ni6 as well as HfO2 nanometer precipitates in the weld, the hardness of the weld zone was higher than that of the base metals.

Peculiarities Formation of Welded Joints under the External Electromagnetic Influence

Controlling the movement of liquid metal by selecting the parameters of an external electromagnetic effect makes it possible to change the conditions of dynamic equilibrium of the weld pool and, as a result, the formation of a weld. Magnetic process control has advantages over mechanical control methods, since it is carried out without contact with the welding zone. The study of processes leading to a decrease in the concentration of defects in metals, recombination of dislocations, polygonization, recrystallization, defect healing, etc., is an urgent task for technologists. The purpose of the work is to study the laws of formation of phase composition, microhardness, grain, lath, subgrain, dislocation structures of low-alloy steel welds in underwater welding and the relationship of structural parameters with the properties of strength and crack resistance of these joints. Microstructure studies were carried out by light, scanning, and transmission electron microscopy. Mathematical modelling was carried out to optimize the research efficiency. The developed computer application implements the idea of sequential calculation of quantities, where the value of the welding current and the current in the inductor is selected by the researcher. The influence of structural factors at the dislocation level on local internal stresses, which determine the deformation localization zones in the structures of the upper and lower bainites in the deposited metal, is analyzed. The conditions for obtaining high-quality welded joints in the welding of low-alloy steels, which ensure their strength and crack resistance, are established.