Fusion Welding Processes Research Articles

Electromagnetic stirring control for resistance spot welding of SiCp/Al composites

Metal matrix composites (MMCs) have broad application prospects in high-end manufacturing fields. However, as typical MMCs, SiC p /Al composites have poor weldability due to the appearance of brittle phase, crack defects, and segregation phenomenon in the fusion welding process. Hence, this paper provides a magnetically assisted resistance spot welding (MA-RSW) method to achieve the reliable welding of SiC p /Al composites. The experimental results show that the MA-RSW technology can significantly extend the weld lobe by increasing the nugget diameter and decreasing the weld penetration, avoid the appearance of the acicular Al 4 C 3 , eliminate weld defects, and homogenize the distribution of the strengthening phase. This facilitates the transformation of the fracture mode from interfacial fracture (IF) to partial thickness fracture (PTF) at low welding current and to button pull (BP) at high welding current in lap-shear tests. Therefore, the weld strength, ductility, and energy absorption ability are greatly improved.

Friction Stir Welding of High Phosphorus Weathering Steel —Weldabilities, Microstructural Evolution and Mechanical Properties

Phosphorus (P) addition is expected to simultaneously increase the strength and corrosion resistance of weathering steels. However, P causes solidification cracking in the fusion welding process and reduces the toughness of the steel. To avoid these problems, the P content of weldable SMA490AW weathering steel is currently limited to below 0.035 mass%. High P steels which are impossible to be joined by the fusion welding process, can be joined by a solid-state joining process, i.e., friction stir welding (FSW). Because the stir zone obtained by FSW contained very fine grains, its toughness was expected to improve. This study applies FSW to high-P weathering steels and examines the weldability of the product. The microstructural evolution and mechanical properties of the stir zone were investigated at different welding temperatures. The macroscopic cross-sectional observations of the FSW joints revealed crack-free structures even in steel containing 0.3 mass% P. Moreover, FSW significantly refined the grain structure in the stir zone. Consequently, the ductile-to-brittle transition temperature of the stir zone was approximately 150°C lower in the steel containing 0.3 mass% P and welded below A1 (average grain size = 2.5 µm) than in the base material (average grain size = 23 µm). It appears that the grain refinement by FSW overcomes the embrittlement caused by excessive P content.

Prediction of relationship between angular velocity to the pitch line velocity (ω/v) on tensile strength of friction stir welded AA2014-T6 Aluminium alloy joints: Angular velocity to pitch line velocity ratio on FSW joints

High-strength aluminum alloys, such as the 7xxx and 2xxx series, are well suited for components and structures. It includes a greater strength ratio and is typically used in fabrication of fuselage and wing skins. AA2014 is difficult to join using a fusion welding process because of its high thermal conductivity, oxidation behavior and low melting point, which can easily lead to burn through and porosity. To alleviate these difficulties, Friction Stir Welding (FSW), a solid-state welding process was deployed. The tool and process parameters are the most vital part in material flow in FSW. The sound welded joints aligned towards the material flow in the weld region under sufficient strain rate. Of which, the angular velocity and pitch line velocity play crucial role in heat generation during the FSW cycle. The effect of angular velocity to pitch line velocity(ω/v) on the tensile properties of the aluminum AA2014 friction stir welded joints was analyzed. To make the joints, five tools with varying shoulder diameter (4 mm, 5 mm, 6 mm, 7 mm, and 8 mm) were used. Microstructure was performed to correlate strength properties of FSW joints. It is found that the joint produced with a ω/vratio of 0.33 exhibited greater tensile properties compared to other joints. It was due to the balanced material flow, development of fine grains and uniform spread of second phase particle in the stir zone.

Friction stir welding of AA2024 and AA6061 using various pin profile

The research work deals with to join two dissimilar aluminum alloys by solid state welding process compared to fusion welding processes and compared with fusion welding process, fusion welds tend to produce more defects while joining dissimilar materials. The major problem of the two dissimilar metals involve in welding process have different mechanical properties and microstructures which in turn may affect welding parameters like weld current, hold time, weld force etc. In order to overcome these issues, Friction Stir Welding (FSW) can be used to get rid of defects since it uses a non-consumable tool and also produces defect free welds compared to other welding processes. This thesis work aims to joining an aluminum alloy of 2024 and aluminum alloy of 6061. The plates are joined by means of octagon probe tool made of high carbon high chromium steel (D2 tool steel). Other issues while welding dissimilar aluminum alloys are phase transformation change and selection of welding parameters (rotational speed, transvers speed, pin diameter, shoulder diameter, D/d ratio and etc.) From conducted trail experiment aluminum alloy of 2024 and aluminum alloy of 6061 by using octagon probe tool made by HC-HCR tool it was observed that a lower welding speed 500 rpm at starting stage lack of filling took place and after thermo-mechanical heating took place that produce better weld while compared to weld at higher speeds (710 rpm, and 1000 rpm) with same transvers speed of 20 mm/min.

Solid-state joining of aluminum to titanium: A review

The dissimilar material joining of aluminum and titanium alloys is recognized as a challenge due to the significant differences in the physical, chemical, and metallurgical properties of these alloys, where the increasing demands for high strength and lightweight alloys in aerospace, defense, and automotive industries. Joining these two alloys using the conventional fusion techniques produces commercially unacceptable sound joints due to irregular, complex weld pool shapes, cracking and low strength, high residual stresses, cracks, and microporosity, and the brittle intermetallic compounds formation leads to poor formability or inferior mechanical properties. The formation of intermetallic compounds is inevitable but it is less severe in solid-state than in the fusion welding process. Hence, this article reviews on aluminum–titanium joining using different solid-state and hybrid joining processes with emphasis on the effect of process parameters of the different processes on the weld microstructure, mechanical properties along with the type of intermetallic compounds and defects formed at the weld interface. Among the various solid-state welding processes for aluminum–titanium joining, the following grades of aluminum and titanium alloys were employed such as cp Ti, Ti6Al4V, cp Al, AA1xxx, AA 2xxx, AA5xxx, AA6xxx, AA7xxx, out of which Ti6Al4V and AA6xxx alloys are the most common combination.

High-strength joint of nuclear-grade FeCrAl alloys achieved by friction stir welding and its strengthening mechanism

Nuclear-grade iron-chromium-aluminum (FeCrAl) alloys are promising candidates for accident tolerant fuel (ATF) cladding materials employed in advanced light-water reactors. Apart from the fusion welding processes, it is necessary to explore available solid-state joining processes such as Friction Stir Welding (FSW) for the FeCrAl alloys. In this study, the feasibility of friction stir welding in the achievement of high-strength Fe-13Cr-5Al alloy joint was investigated. The results demonstrated that a nuclear-grade FeCrAl alloy joint with nominal ultimate tensile strength of ∼629 MPa and fraction elongation of ∼19 % was successfully fabricated using friction stir welding (FSW). For the first time, the joint efficiency of FeCrAl alloys was approximately 100 % or better according to microhardness and tensile tests. Texture in the stir zone (SZ) consisted of a mixture of J ¯ 1 ¯ 1 ¯ 0 [ 1 ¯ 1 2 ¯ ] , D 1 1 ¯ 1 ¯ 2 [ 111 ] , D 2 1 ¯ 1 ¯ 2 [ 111 ] , and E ¯ 1 ¯ 1 ¯ 0 [ 1 ¯ 11 ] components due to severe simple-shear strain. Microstructures in the SZ were predominately refined through discontinuous dynamic recrystallization (DDRX) due to the high-density of high-angle grain boundaries (HABs) and the abundancy of triple junctions induced by the increased strain. The excellent properties of the FeCrAl alloy joint were attributed to the formation of high-density low-angle boundaries (LABs) and refined grain structures. The fundamental discoveries in this study reveal a promising application prospect of FSW in the joining of nuclear reactor ATF cladding materials.

Experimental and Theoretical Investigations on Cold Metal Transfer Welds Using Neural Networks: A Computational Model of Weld Geometry

Cold metal transfer (CMT) welding is a sophisticated version of fusion welding process available with advanced features incorporated in it. During the process of joining metallic parts with CMT, the bead shape and size have significant effects on the weld quality. Typically, bead geometry is characterized by the three important parameters namely weld width, weld depth and reinforcement height. For rapid and intelligent welding, it is imperative to monitor the bead shape and size during the process. However, the measurement system of three parameters is often time consuming and complex. In this paper, an attempt is made to reduce the computational time of artificial intelligence models that are used for intelligent welding processes. Bead coefficient is modelled as an alternative for bead geometry properties. Computationally efficient artificial neural network models are developed for examining the feasibility of bead coefficient over bead geometry properties with and without online-temperature measurements. The predicted results of both forward and reverse neural network models are in good coherence with the experimental values. The outcome of this study is expected to provide a detailed understanding of effects of process parameters on bead geometry and bead coefficient, which facilitates online monitoring of welding processes.

Joining of aluminium to polymer by friction stir welding: An overview

Friction stir welding (FSW) is a potential fabrication method to join the aluminium and polymer dissimilar materials as FSW joins the metals below their melting point. Since the automobile and aviation industries replacing the heavier metals with the lighter one like aluminium and polymer therefore joining of these two materials is the requirement for the industries in the current time. A lot of studies have been already done to join these two materials in the lap, butt and t-joint configuration. Particular attention has been focused to macrostructural and microstructural evolution after welding, microhardness and tensile property. As the temperature is an important factor for both the polymer and aluminium due to difference in chemical and mechanical property, so FSW is a suitable technique compared to other fusion welding processes therefore improved joint property is expected. In the present study, process capability of FSW has been enlightened for joining aluminium-polymer materials for future prospective…

Experimental Review on Friction Stir Welding of Aluminium Alloys with Nanoparticles

To reduce environmental impacts and ensure competitiveness, the fabrication and construction sectors focus on minimizing energy and material usage, which leads to design requirements for complex structures by joining of similar and dissimilar materials. Meeting these industrial demands requires compatible materials with improved properties such as good weight-to-strength ratios, where aluminum (Al) and its alloys are competing candidates for various complex applications. However, joining Al with fusion welding processes leads to joint deterioration. Friction stir welding (FSW) produces joints at temperatures below the melting temperature, thus avoiding flaws associated with high heat input, yet requires improvement in the resultant joint properties. Recent studies have shown that nanoparticle reinforcement in FSW joints can improve weld properties. The main focus of this study is to critically review similar and dissimilar friction stir welding of AA5083 and AA6082 with carbide and oxide nanoparticle reinforcement. The study also discusses the effect of welding parameters on reinforcement particles and the effect of nanoparticle reinforcement on weld microstructure and properties, as well as development trends using nanoparticles in FSW. Analysis shows that friction stir welding parameters have a significant influence on the dispersion of the reinforcement nanoparticles, which contributes to determining the joint properties. Moreover, the distributed nanoparticles aid in grain refinement and improve joint properties. The type, amount and size of reinforcement nanoparticles together with the welding parameters significantly influence the joint properties and microstructures in similar and dissimilar Al welds. However, research is still required to determine the strengthening mechanism used by nanoparticles and to assess other nanoparticle additions in FSW of Al alloys.

Real-time data assimilation and control on mechanical systems under uncertainties

This research work deals with the implementation of so-called Dynamic Data-Driven Application Systems (DDDAS) in structural mechanics activities. It aims at designing a real-time numerical feedback loop between a physical system of interest and its numerical simulator, so that (i) the simulation model is dynamically updated from sequential and in situ observations on the system; (ii) the system is appropriately driven and controlled in service using predictions given by the simulator. In order to build such a feedback loop and take various uncertainties into account, a suitable stochastic framework is considered for both data assimilation and control, with the propagation of these uncertainties from model updating up to command synthesis by using a specific and attractive sampling technique. Furthermore, reduced order modeling based on the Proper Generalized Decomposition (PGD) technique is used all along the process in order to reach the real-time constraint. This permits fast multi-query evaluations and predictions, by means of the parametrized physics-based model, in the online phase of the feedback loop. The control of a fusion welding process under various scenarios is considered to illustrate the proposed methodology and to assess the performance of the associated numerical architecture.

Influence of D/d ratio on stir zone formation and properties of friction stir welded dissimilar joints of AA5086 and AA6061 aluminum alloys

A well-known method known as Friction stir welding (FSW) is used for combining materials that are distinct from each other. In FSW, a profiled spinning shoulder shifts between sheets of the sections that are to be connected. Heat is produced due to the friction between the base and the tool shoulder when the tool is turning along the weld line. In contrast to fusion welding processes, the heat produced is lower. In these works, the effect of macro/microstructures characterization and the tensile characteristics of the dissimilar AA5086 and AA606I aluminum alloys on the ratio of tool shoulder diameter and tool pin diameter (D/d) used in the FSW were explored. This study shows the superior tensile characteristics on welding components in contrast to the counters made of the sealing units made using a tool profile of threaded cylinders, a 1 ° tool tilting angle, tool rotation speed of 1100 rpm, the welding speed of 22 mm/min and the shoulder diameter is 21 mm. Further, the joints fabricated using threaded cylinder tool profile exhibited superior macro structure compared to its counter parts.

Comparing Methods for Computing the Electrical Superconducting Property With Microstructure of Electron Beam Welded High Purity Niobium

This article focuses on the effect of grain size on estimating the residual resistivity ratio (RRR) of electron beam welded (EBW) high purity Niobium (Nb) for the structural fabrication of radio frequency cavity as a particle accelerator. This also aims to investigate the effects of using different functional models on resistivity. EBW is done by varying the beam current to change the grain size so that its consequent impact on RRR can be evaluated. Grain size was found to be maximum for 70 mA and minimum for 50 mA beam current among the welded samples at HAZ and FZ. The grain size increases from the base metal toward the heat-affected zone and further to the fusion zone like any other fusion welding processes. Pure Nb being electrically superconductive below around 9.2 K in the absence of any magnetic field, it is invariably used as a resonant cavity for a particle accelerator in high energy physics. Two temperature dependent and two field dependent models are used for extrapolation of the RRR value estimation. Temperature dependent models performed the better-fitted residuals for every sample than the field models. The extrapolated RRR values obtained from these models are used to simulate the impact of beam current on grain size at different zones of welding.

Microstructure and Mechanical Properties Relationship of Friction Stir- and A-GTA-Welded 9Cr-1Mo to 2.25Cr-1Mo Steel

Dissimilar weldment of 9Cr-1Mo (P9) to 2.25Cr-1Mo (P22) steel processed with fusion welding process must be subjected to post-weld heat treatment (PWHT) prior to operation due to the presence of martensitic microstructure in the weld. However, due to the gradient of carbon activity, PWHT results in the diffusion of carbon from low Cr to high Cr side, which results in a soft zone and hard zone formation in the weld. This would degrade the mechanical properties of the weld joint. In order to tackle this, the present study employed friction stir welding (FSW) process at two different rotational speeds via 200 and 500 rpm. The microstructure and mechanical properties of the FSW specimens were compared with that of activated-gas tungsten arc (A-GTA) weldments. Regardless of the tool speed, the FSW and A-GTA processed specimens indicated martensitic microstructure in the weldment, and hence, PWHT was carried out. The PWHT treated FSW specimen revealed soft and hard zone evolution throughout the weld matrix, whereas in A-GTA welds, no severe diffusional phenomenon was observed across the weld. The A-GTA weld joint exhibited better strength properties than that of the weld joint made by FSW process, and therefore, A-GTA welding can be suitable techniques for welding of P9–P22 steel.

Current advancements in friction stir welding of high density materials: A review

In today's industrial sector, welding seems to be a very essential procedure required for the manufacture and renovation of metal products. Scientists are continuously searching for the right forms of welding to be used for different joints. This growing interest will contribute to the use of dissimilar alloys that involve welding. Owing to energy efficiency and environmental friendliness, Friction stir welding (FSW), extremely efficient solid-state joining method, was being referred to as “green” technology. This is an emerging paradigm for joining metallic components, in specific compact high-strength alloys that have been known as non-weldable by conventional fusion welding. This is also recognized as being the most important breakthrough in the field of material integration over the last couple of decades. As in the current context, welding of metallic materials is substituted through FSW due to its special characteristics across fusion welding processes, i.e. lowered heat-affected zone (HAZ), significantly lower porous defect, eco-friendly, minimized distortion, no gas shielding requirement, etc. This review article provides a framework for engineers and designers to explore FSW for a broader variety of different materials. Applications, challenges as well as other factors relevant to FSW are also discussed to provide guidelines for the worldwide scientific community to undertake comprehensive research in this area. This review ends with suggestions for the future direction of study.

Investigations on GTAW and FSW of Al6061-ZrB2-Fly ash hybrid metal matrix composites

Various hard ceramic particles, carbonaceous, organic, fibers, and other materials are used to reinforce aluminum alloys. These composites, identified as aluminum metal matrix composites possess low density, high strength, low thermal expansion, and strong structural rigidity. In this research work, a comparison of the traditional fusion welding method (GTAW) and Friction Stir Welding (FSW) in joining such composites is carried out. Suitable parameters for the welding process are estimated to join Al6061-ZrB2-fly ash composites. The mechanical or physical properties of the parent metal and weldments, such as tensile strength and hardness, are investigated. In addition, their microstructure correlations are also evaluated. It is found that the physical properties of the parent metal have improved as a result of the variations in the reinforcements. At the higher percentage of the reinforcement, the properties have deteriorated due to the excess slag accumulation. The fusion welding process yielded better mechanical properties than the solid-state welding system in the comparative analysis. This is attributed to the efficiency of the fusion welding process for joining composites of this kind. Despite the fact that the solid-state welding process produced better microstructures in the weld region, particle segregation occurred, lowering the properties. Unlike other studies, the microstructure of the fusion-welded samples here has greater integrity and less particle segregation. Grain refining has also occurred, resulting in improved mechanical properties.

Experimental and numerical study to minimize the residual stresses in welding of 6082-T6 aluminum alloy

One of the most important negative consequence in the fusion welding processes is the generation of tensile residual stresses in welded joints. The main goals of this work are to determine the optimal combination of welding parameters to minimize the residual stress level and the influence of each welding parameter in that feature to weld 6082-T6 aluminum alloy plates using the GMAW welding process. To achieve these goals was implemented the Taguchi orthogonal array (L27) to define the design of numerical and experimental tests. All combinations were simulated in the Simufactwelding 6.0 software, from which it was possible to obtain the values of maximum residual stresses. The data treatment was carried out, reaching the combination of levels for each parameter. With ANOVA analysis was found that the parameter with the greatest influence in the residual stress generation was the welding speed, while the parameter with the least influence was the torch angle. Also, to minimize the residual stresses it was observed that the optimal combination of welding parameters is welding current intensity of 202 A, welding speed of 10 mm/s, and 30° of inclination of the angular torch. The two simulations that resulted in the highest and lowest residual stresses were validated experimentally by the hole drilling method to measure the residual stresses.

Weldability and mechanical properties of AA5052 and AA7075 dissimilar joints developed by GTAW process

Study of the weldability and mechanical behavior of bimetallic welds of AA5052 and AA7075 obtained from gas tungsten arc welding process was done. Two filler wires viz., ER4043 and ER5356 were employed to join the dissimilar metals. The process parameters and welding conditions were used same in both filler weldments. Non-destructive testing was carried out to confirm the weldability of dissimilar joint with fusion welding process. The mechanical tests such as tension, hardness and impact test were conducted as per ASTM standards to evaluate the weld properties. Weldments obtained using ER4043 filler has exhibited superior quality with UTS of 182 MPa. It was found that the welds of ER 4043 have shown higher impact strength of 62 J whereas weldment obtained by ER 5356 has given toughness value of 24 J. The micro-porous and voids were observed in weld zone when ER5356 filler was employed.

Investigation on mechanical and microstructure characteristics of nickel based C-2000 super alloy using laser beam welding

The main aim of the research is to investigate the microstructure and mechanical properties of advanced corrosion resistant alloy C-2000 welded with Laser Beam Welding (LBW) process. Laser welding is a high-power-density fusion-welding process that produces high aspect ratio welds with a relatively low heat input compared with other arc-welding processes. Dinolite macro analyzer was used to determine the aspect ratio and other defects in the weld joint. The micro structural characteristics of the weldment are analyzed with Optical and Scanning Electron Microscope (SEM). The micro segregation of alloying element in interdendritic regions is quantified by Energy dispersive X-ray spectroscopy (EDS). Microstructure examination shows that mild copper microsegregation is observed near the interdendritic region. The strength, ductility, hardness and toughness of weld joints are evaluated by tensile, Vicker’s hardness and Charpy impact test respectively. The result outcome shows that mechanical properties are slightly lower than base metal due to the combined existence of columnar and equiaxed grains in the weld fusion zone.

Mechanical properties and microstructural characteristics of rotary friction welded dissimilar joints of rolled homogeneous armor steel and medium carbon steel

Abstract Distinct materials are used for the construction of battle tanks used in defense sectors. The hull and turret of the battle tanks are made up of rolled homogeneous armor steel (also known as armor steel). The inner portions like the driver cabin and control room are covered with medium carbon steel. Hence, the dissimilar joint between these materials is unavoidable in the battle tank construction. Conventional fusion welding processes like manual metal arc welding, gas metal arc welding, and gas tungsten arc welding are preferred to join the dissimilar metals. However, the high heat input nature of these processes will create hydrogen induced cracking, high residual tensile strain, and HAZ softening, etc. To minimize these issues, solid state welding processes were adopted. In the present study, mechanical properties and microstructural characteristics of rotary friction welded dissimilar joint of armor steel and medium carbon steel was analyzed. The ultimate tensile strength of the dissimilar joint is around 775 MPa and the failure occurred at the medium carbon steel side. The impact toughness value of dissimilar joints is higher than medium carbon steel and lower than armor steel. The microstructure across the dissimilar joint has distinct features and a complex pattern was observed at the weld interface.

Fracture behaviour of friction stir welded dissimilar aluminium alloys

High strength aerospace grade aluminium alloys are considered difficult to be welded by conventional fusion welding processes but Friction stir welding (FSW) process can effectively join these alloys with good joint properties. FSW is being widely used in aircraft construction and tank of space shuttles. After successful joining of Aluminium alloys by FSW, the fracture behavior of the joint need to be investigated for analyzing the joint fracture. In the present paper, dissimilar aluminium alloys were welded successfully at a rotational speed of 710 rpm, traverse speed of 160 mm/min and tool shoulder diameter of 12 mm. The welded joint was tested on tensile testing machine and the fracture location was found to be at heat affected zone (HAZ) of advancing side. HAZ was found to be the weakest portion of the joint due to thermal softening which resulted in grain growth and large-sized coagulated precipitates. Cracking of large-sized coagulated Al2Cu precipitates resulted in the fracture of the welded joint.