Welded Samples Research Articles

Weldability Investigation and Optimization of Process Variables for TIG‐Welded Aluminium Alloy (AA 8006)

Aluminium and its alloys play a significant role in engineering material applications due to its low weight ratio and superior corrosion resistance. The welding of aluminium alloy is challenging for the normal conventional arc welding processes. This research tries to resolve those issues by the Tungsten Inert Gas welding process. The TIG welding method is an easy, friendly process to perform welding. The widely applicable wrought aluminium AA8006 alloy, which was not considered for TIG welding in earlier studies, is considered in this investigation. For optimizing the number of experiments, the Taguchi experimental design of L9 orthogonal array type experimental design/plan was employed by considering major influencing process parameters like welding speed, base current, and peak current at three levels. The welded samples are included to investigate mechanical characterizations like surface hardness and strengths for standing tensile and impact loading. The results of the investigation on mechanical characterization of permanent joint of aluminium AA8006 alloy TIG welding were statistically analyzed and discussed. The 3D profilometric images of tensile‐tested specimens were investigated, and they suggested optimized process parameters based on the result investigations.

Retracted] Improvement on Mechanical Properties of Submerged Friction Stir Joining of Dissimilar Tailor Welded Aluminum Blanks

Friction stir welding is a solid‐state welding method that produces joints with superior mechanical and metallurgical properties. However, the negative effects of the thermal cycle during welding dent the mechanical performance of the weld joint. Hence, in this research study, the joining of aluminum tailor welded blanks by friction stir welding is carried out in underwater conditions by varying the welding parameters. The tensile tests revealed that the underwater welded samples showed better results when compared to the air welded samples. Maximum tensile strength of 229.83 MPa was obtained at 1000 rpm, 36 mm/min. The improved tensile strength of the underwater welded samples was credited to the suppression of the precipitation of the secondary precipitates due to the cooling action provided by the water. The lowest hardness of 72 HV was obtained at the edge of the stir zone which indicated the weakest region in the weld zone.

A study on thermo-mechanical analysis of ultrasonically welded dissimilar alloys for automotive application

Abstract Ultrasonic spot welding (USW) method has the capability to produce highly efficient solid-state bonds in lightweight alloys with minimum power consumption. Unlike fusion welding techniques, this technique utilizes less energy and produces superb joint quality with refined grain structures and minimal intermetallic compounds (IMCs). This method has been receiving attention progressively in the material joining field because of its advantages like environmentally friendly, shorter weld time, and involvement of low temperature. Thus, these properties make this process suitable for welding of malleable thin metal sheets. During the USW process, it is noticed that the effect of intensive material contact increases when the weld progresses, and it leads to the frictional heating and plastic deformation phenomena. Subsequently, it results in the change of mechanical and microstructural characteristics at the weld zone. To reduce the forming load and static stress distribution from the welded samples, it is necessary to analyze the thermo-mechanical properties of ultrasonically welded joints. In the current study, various aspects of ultrasonic energy on material deformation and temperature variations are investigated using the finite element analysis (FEA). As a result, several types of features are noticed in the weld region with different forming morphologies. To further explore the effect of weld process parameters on the weld interface of this dynamic process, the strength and fracture in USW are also studied.

Determination of Tensile Shear Strength and Corrosion Behavior of Circular Bead Produced by a Laser Beam for Overlapped AISI 304 Steel Sheets

Abstract: A circular bead produced by a laser beam (CLW) is a method of joining superposed sheets by scanning circularly a laser beam. Among the various applications, it could be highlighted the welding of austenitic stainless steel AISI 304 sheets for heat exchangers. This work aims to report the effect of fiber laser CLW in tensile shear strength of superposed sheets as well as the corrosion behavior in relation to the process parameters. It was carried out circular beads using stainless steel AISI 304 sheets varying the laser power and speed. The samples were then submitted to optical and electronic microscopy, tensile-shear tests and electrochemical experiments. Among the experimental conditions, the weld sample with 800 W power and 50 mm/s speed presented an ultimate tensile strength of 159 MPa, 17% higher than the sample with the lowest result. The corrosion rate, corrosion and pitting potentials did not change significantly in the welded joint with different conditions compared to the base metal.

ОСОБЕННОСТИ РЕМОНТА СВАРНЫХ КОНСТРУКЦИЙ БОЛЬШИХ ТОЛЩИН ИЗ ТИТАНОВОГО СПЛАВА ВТ6ч.

The technology of electron-beam welding (EBW) of structures of large thickness made of titanium alloy Ti–6Al–4V has been developed. A complex of metallographic studies of welded samples has been carried out. Tests to determine the mechanical characteristics of repair welded joints, that these joints made by EBW are equal in strength to the base material. The analysis of the level of residual stresses in various parts of the welded joint after repeated repair passes has been carried out. It was found that the subsequent vacuum annealing reduces the level of residual stresses in welded joints to 50 %. The analysis of the elemental composition showed that the elemental composition of the samples from the center of the weld to the base metal practically does not change for welding with the number of repeated passes up to 3.

A study of the influence of high frequency cyclic loading on the structure and properties of weld connections in process pipelines

Introduction. Pipeline systems are exposed to several conditions that lead to a drastic reduction in their durability, primarily due to variable low-frequency and high-frequency loads arising in a process pipeline due to the operation of compressor units. Hence, fatigue failure occurs, leading to the pipeline failure. As early as at the pipeline installation stage, sections of process pipelines have weld connections, and thermal welding cycles have an adverse effect on the properties of materials exposed to fatigue loading. The study of weld connections in steel pipelines exposed to high-frequency vibrations and effects of weld seam defects on durability characteristics are the focus of this research.
 Materials and methods. Low-carbon pipeline steel St20 was selected for the study. The radiographic inspection method, optical metallography, microhardness of structural phases, and the method of high-frequency fatigue tests were used.
 Results. The results and principal conclusions about the effect of welding defects on durability characteristics of welded samples, made of pipeline steel and exposed to high-frequency fatigue tests, are presented; structural changes in weld connections are analyzed using optical metallography and microhardness methods. Defects of weld seams and their dimensions were identified by means of radiographic inspection. A comparative analysis of durability limits, demonstrated by the parent metal of the model material that has defective weld connections, and the same limits of defect-free samples is provided. The main causes of failure of weld joints, exposed to high-frequency vibrations, are identified.
 Conclusions. Having summarized the research findings, we can argue that high-frequency vibrations have a negative impact on the parent metal of a process pipeline and its weld joints. The weld seam is the point of failure; defects trigger destruction, and their presence has a higher impact on fatigue characteristics than their dimensions or types. Characteristics of durability in case of exposure to high frequency loading applied to a weld joint in the gigacycle range are 67 percent below those of the parent metal.

Microstructure and mechanical property evolution of post weld heat treated bainitic steel welds

Abstract The achievement of excellent combination of high tensile strength and good ductility has been the key factor that facilitates the Advanced High Strength Steels (AHSS) to be the candidate materials for automotive applications. Carbide free bainitic steels are a class of AHSS that primarily have microstructure consisting blend of fine bainitic laths and interwoven retained austenite in the interlath boundaries of bainite. Solid state welding techniques are regarded to be the most sought after fabrication processes as they result in retention of basic microstructural constituents, especially nonequilibrium phases like bainite. Keeping this fact in view, friction stir welding was carried out on 3 mm thick carbide free bainitic steel plate with varying tool rotational speeds. The temperatures of stir zones were recorded. The microstructural changes and phase analysis from base metal (BM) to Thermomechancally Affected Zone (TMAZ) and Stir Zone (SZ) were studied. The microhardness profiling was done across the weld covering the BM, TMAZ and SZ. The abrupt increase in the hardness of stir zone and microstructure stability i.e., retention of bainitic microstructure along with the retained austenite were observed. The tool rotational speed of 150 RPM has been optimized. Post weld heat treatments were undertaken at different temperatures and increased soaking time on the welded samples of optimized rotational speed to facilitate bringing down the stir zone hardness to the base metal. Basing the phase analysis and EBSD data obtained, the post weld heat treatment cycle conducted at 500OC with a soaking time of 1 h has been optimized.

A study on plasma keyhole welding of stainless steel grade 316

A metal joining method called plasma keyhole welding is used to achieve narrow and deep penetration. The best parameter combination for the welding process is known to produce high-quality weld joints. A study on the plasma keyhole welding for joining stainless steel grade 316 is carried out in this paper, which is the first attempt to optimize plasma welding parameters for stainless steel grade 316. During the welding process, various welding parameters such as welding current, welding speed and gas flow rate are considered and varied to determine the effect of such parameters on the welded joint. The physical properties of the welded samples, such as tensile strength and microhardness, were investigated. With the combination of welding current of 180 A, a welding speed of 260 mm/min, and a plasma gas flow of 2.5 l/min, the maximum value for tensile properties and hardness is achieved. Components made of stainless steel grade 316, which are employed in the areas where higher load-bearing properties are necessarily required can be joined by the plasma welding process with the experimentally determined optimum parameters.

Magnetic Technique Estimation of Weld Residual Stress Failure Due to Tensile Loading

In Nigeria, most welding activities are carried out by road side welders, majority of this welders are ignorant of weld residual stress and its adverse effect on weldment. Residual stress (RS) measuring device is vital in the measurement of inherent stresses in material. The aim of this research was to employ proof of principle in analyzing the weld residual stresses in a material. This was achieved by measuring samples with magnetic residual stress device and then subjecting the weld samples to mechanical tensile test with hope that materials with more residual stresses fail first. Finally the result from both procedures was compared to establish a relationship. Four (4) pieces of mild steel coupons measuring 100 × 40 × 3 mm were welded, producing two specimens, A11 and B11 of 200 × 40 × 3 mm, respectively. The specimens were measured using the Magnetic device developed and 37 signals were obtained per specimen, thereafter, the welded specimens were subjected to tensile testing and results analyzed. From the results obtained, Specimen A11 was observed to have the highest signal peak at the weld zone with RS signal of 20.3983 mV compared to B11 with 19.358 mV. While under tensile loading, it took 1.63 kN to cause failure to specimen A11 and 8.65 kN for specimen B11. From this simple experiment, it implies that the Magnetic RS device was able to mimic the behavior of residual stress and also predicted that A11 would fail first.

Low-temperature thermoplastic welding of metallic glass ribbons for in-space manufacturing

In-space manufacturing is an emerging and promising research field in space industry, which benefits the development of space explorations. Owing to the microgravity, high vacuum and complexity of the space environment, a special manufacturing strategy for alloys is highly demanded for the in-space manufacturing. Herein, a low-temperature thermoplastic metallic welding method was proposed and employed for La-based metallic glass ribbons. With the sandwiched structures of La- and Zr-based ribbons, the welded samples exhibit a competitive fracture strength and an increased tensile strain than those of the welded la-based samples due to the second phase strengthening. This suggests that metallic glass is an ideal material candidate for in-space manufacturing, and can be well manufactured at a nonmelting state with good mechanical performances. In addition, the thermoplastic manufacturing method can also feature a moderate processing time window. In general, this work presents the promising potential of low-temperature thermoplastic welding strategy for in-space manufacturing of metallic materials.

The structural integrity of flash-butt welded premium rail steel – Evaluation of strength, microstructure and defects

Experimental testing of flash-butt welded premium rail steel samples was undertaken to quantify the variation in strength through the cross-section of the weld, with results showing a general correlation between the width of the heat-affected-zone and the ultimate tensile strength. Microstructural examination and fractography revealed the presence of defects in some samples. Large defects can be identified by non-destructive testing methods as part of routine structural integrity assessment; however, small defects may escape detection but could propagate under cyclic loading in service leading to catastrophic failures. This work demonstrates the requirement for stringent control of heat input to prevent the development of defects in premium rail steels with high alloying content.

Optimization of process parameters of friction stir spot welding of polycarbonate sheets and morphological analysis

AbstractFriction stir spot welding has a great impact on the joining process of thermoplastics. In this work, effects of varying rotational speed, plunge depth, and dwell time were investigated on polycarbonate sheets and a filler sheet was utilized to reduce the keyhole size of friction stir spot welded joints. The welding parameters were arranged according to Taguchi L9 orthogonal design of experiments to determine the optimum levels of process parameters. Lap shear tests were performed to examine the mechanical properties. Using analysis of variance and signal to noise ratio, influences of each welding parameter on the lap joint shear load were evaluated. According to achieved results, tool rotational speed has the highest effect while plunge depth has minimum effect on the mechanical behavior of friction stir spot welded joints. Optimum process parameters were attained as 1000 min−1 for rotational speed, 10.5 mm of plunge depth, and 40 s of dwell time. Optimized process parameters showed 15 % improvement compared to the initial welding parameters. Cross‐sectional appearances of welded samples which play an important role in determining lap joint shear load were analyzed by morphological and visual comparisons. Failure modes of the fractured samples for lowest, moderate and highest lap joint shear loads were also observed.

Microstructural and mechanical characterization of the effect of the welding process on creep behavior of welded joint and base metal specimens of Inconel 600

AbstractIn this study, plates of Inconel 600 superalloy were gas metal arc welded to investigate the effects of the welding process on the creep behavior of the welded samples and compare it to the creep behavior of samples in the as-received condition. Creep tests were performed at two temperatures (600 and 650 °C) with different stress levels. During the welding process, three distinctive microstructural zones are generated, i.e. welded material, heat affected zone, and base metal that may affect the properties of the welded joint. Microstructural, elemental analysis of samples was conducted using Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The experimental results show that creep rupture preferentially occurs in the heat-affected zone of the base metal at 4 mm from the fusion line and that the creep behavior of welded samples is different from that of the base metal. These results can be used in the design of structural components to assure their structural integrity.

Influence of Stick Electrode Coating’s Moisture Content on the Diffusible Hydrogen in Underwater Wet Shielded Metal Arc Welding

Abstract In shielded metal arc welding, the major factors influencing hydrogen uptake into the weld metal are (i) the hydrogen content of the base metal, (ii) hydrogen input by the welding consumable, and (iii) the hydrogen introduced by the atmosphere surrounding the arc process. In this study, the relative contribution of these factors is investigated and compared to each other for the case of underwater wet shielded metal arc welding. To assess the influence of the stick electrode’s moisture (capillary introduced water during handling operations) on the diffusible hydrogen in wet welded samples, wet and dry electrodes were welded at four different water depths. The moisture was absorbed through the sharpened electrode tip only, to ensure close to service conditions. The results show that the moist stick electrode coatings lead to 22.6% higher average diffusible hydrogen content in the weld metal (0.5 m water depth an average). However, the effect disappears with increasing water depths (no difference in 60 m water depth).

Residual Stresses and Microstructural Features of Rotary-Friction-Welded from Dissimilar Medium Carbon Steels

The purpose of the present study was to fulfill the knowledge gap concerning the residual stress distribution in dissimilar medium carbon steels welded by a rotary friction technique. For this purpose, residual stresses were evaluated by X-ray diffraction. Microstructure observations, microhardness measurements and tensile tests were performed to couple all information. In addition, the distribution of residual stresses was evaluated in welded samples heat treated at 300 and 600°C. We have found that the residual stress distribution is in the high compression in thermomechanical affected zones, due to the microstructural changes during the welding process. Two subzones form the thermomechanical affected zone. However, the heat treatments caused a relaxation phenomenon in the weld region which is due to the recrystallisation during the heat treatments.

Superplastic behaviour and solid state weldability of a polycrystalline heavily alloyed nickel-base superalloy

Effective thermomechanical treatment has been developed for the heavily alloyed Ni- base superalloy produced via ingot metallurgy with a high content of γ’-forming elements. It allowed us to eliminate dendritic segregation and to obtain a uniform fine-grained structure with a γ grain size of d=5-15 μm. In the fine-grained condition the superalloy exhibited superplastic properties at 1125-1175°C (δ>300%, σ=10-27 MPa, m>0.3). Pressure welding experiments were performed at 1150°C for samples with the fine-grained structure. The solid-phase joint was formed only after compression to the strain of 50%. It was shown that insertion of a nanocrystalline interlayer of the same superalloy between the welded samples facilitated formation of the solid-phase joint.

Friction Stir Welding Parameters: Impact of Abnormal Grain Growth during Post-Weld Heat Treatment on Mechanical Properties of Al–Mg–Si Welded Joints

Friction stir welding (FSW) is an alternative method to join aluminum (Al) alloys in a solid-state condition. However, the coarsening or dissolution of precipitation hardening phases in the welding zone causes strength reduction or softening behavior in the welded area of age-hardened Al alloys. Therefore, this research aimed to improve the mechanical properties of an FSW Al–Mg–Si alloy via post-weld heat treatment (PWHT) and the possibility of controlling the abnormal grain growth (AGG) using different welding parameters. FSW was performed with different rotational and travel speeds, and T6 heat treatment was carried out on the FSW samples as the PWHT. The results showed a decrease in the strength of the FSW samples compared with that of the base material (BM) due to the dissolution of precipitation hardening particles in the heat-affected zone. However, the emergence of AGG in the microstructure after the T6-PWHT was identified as the potential event in the microstructure of the PWHT samples. It is found that the AGG of the microstructure in similar joints of Al6061(T6) was governed by the welding parameters. The results proved that PWHT was able to increase the tensile properties of the welded samples to values comparable to that of Al6061(T6)-BM. The increased mechanical properties of the FSW joints were attributed to a proper PWHT that resulted in a homogeneous distribution of the precipitation hardening phases in the welding zones.

Influence of corrosive wear on hull strength of sea-going ships

Object and purpose of research. This paper discusses hulls of ships, both in-service and under construction. The purpose of the research is to evaluate and monitor the effect of corrosion wear on their global and local strength.
 Materials and methods. Corrosion wear was taken into account on the basis of the methodology of the Rules of the Russian Maritime Register of Shipping and service life test data for hull samples. The assessment of the corrosive wear effect on the local strength of the plates was carried out using the finite element method.
 Main results. The corrosive wear effect on the parameters of global and local strength of ship hulls is considered. Experimental fatigue curves are obtained from service-life test results for welded samples with and without corrosive wear. Numerical modeling of the change in the stress-strain state of the plate on the size and number of corrosion pits is performed. Various methods of accounting for corrosive wear in the rules of international and indigenous classification societies are considered.
 Conclusion. The obtained results demonstrate and confirm the need to take into account corrosive wear when calculating the overall and local strength of new and used ship hulls.

Fatigue life of the welding seam of a tracked vehicle body structure evaluated using the structural stress method

The supporting roller is an important component in the driving systems of tracked vehicles. Through the bracket structure, the supporting roller is bolted to the vehicle body welded with a reinforced metal plate, providing vertical support and lateral guidance of the track. The strengthening weld structure between the bottom plate and the vehicle body is the root of the cantilever beam, where stress is concentrated and fatigue damage is easily accumulated. The fatigue life of the whole vehicle is affected by the fatigue damage in this part. This paper proposes a structural stress method to evaluate the fatigue life of the welding seam of a tracked vehicle body. Further, the proposed method is evaluated under typical road-load spectra. Initially, the base-metal and weld structures were subjected to monotonic tensile and cyclic plastic deformation tests. The tensile strength of the weld sample was approximately half of that of the base metal. Next, the welded structure of the supporting roller bracket was simulated using a finite element model. The calculated stresses were consistent with the fatigue crack locations in the welded structure. The structural stress was not dependent on the grid density. Subsequently, multibody dynamic simulations of the whole tracked vehicle were performed on four standard road surfaces constructed using the harmony superposition method. The road-load spectra at the axle head of the supporting roller were calculated under four pavement conditions, and the fatigue life of the weld structure of the supporting roller bracket was determined. The calculated fatigue life was considerably lower than the designed fatigue life. Finally, the initial weld structure was redesigned by increasing the size of the strengthening metal plate and the weld length. The fatigue life of the redesigned structure was considerably longer than that of the original structure, indicating that the proposed method can effectively analyze the fatigue life of the welding seam and that it can be used to optimize the design scheme.

Investigation of Weld Zone and Fracture Surface of Friction Stir Lap Welded 5052 Aluminum Alloy and 304 Stainless Steel Joints

Dissimilar material joining of aluminum and steel in the present scenario is an important criterion in the manufacturing industry, especially because of their low weight and technical performance. In the present investigation, AA5052 and SS304 are friction stir welded in lap configuration with different tilt angles, welding speed, pin depth, and tool rotational speed, with aluminum as the top plate. A maximum of 3.16 kN shear strength was achieved at 2.5° tilt angle when the penetration depth was 4.3 mm. The shear strength samples were studied for fracture analysis and it was found that fracture of the samples mainly occurred on the aluminum side and the fracture demonstrated both brittle and ductile failure, consisting of quasi-cleavage, trans-granular, and intergranular fracture areas. Field emission scanning electron microscope images at the interfacial region of the weld show that different intermetallic compounds were formed at various zones of the joint with respect to the change in process parameters. It was observed from energy dispersive spectroscopy that Al-rich intermetallic compounds were formed at the interfacial region of the welded samples. Amongst the process parameters, change in the tilt angle affected the weld zone significantly. The thickness of the intermetallic compound (IMC) layer formed with 800 and 1000 rpm at 2.5° tilt angle was between 2.5 and 3 μm, which resulted in achieving better joint strength. AlFe, AlFe3, Al13Fe4, and Al5Fe2 were the different intermetallic compounds detected using X-ray diffraction with different process parameters. The hardness of the samples ranged between (300 and 630) HV, which further supports the formation of AlFe and AlFe3 intermetallic compounds.