Conventional Welding Processes Research Articles

Comparative study on microhardness between friction stir welding and tungsten inert gas assisted friction stir welding of pure copper

Welding copper and its alloys is usually difficult to achieve by conventional fusion welding processes because of high thermal diffusivity of copper, which is at least 10 times higher than most steel alloys. In order to reduce the increased temperature loss, it would be advantageous to use a process that is carried out at lower temperatures. Friction Stir Welding (FSW) is a solid state joining process that involves the joining of two metal pieces at the molecular level without melting and was explored as a feasible welding process. In order to achieve an increased welding speed and a reduction in tool wear, this process is assisted by another one (TIG - tungsten inert gas) which generates and adds heat to the process. The research includes two experiments for the FSW process and two experiments for TIG assisted FSW process. It is presented the evolution of the temperature and of the axial force during the process and is determined the microhardness for each experimental case. The aim of this paper is to make known the effects of using TIG assisted FSW process on the microhardness of the pure copper joints and to present some conditions in which it is less affected.

Friction stir welding of Aluminium matrix composites – A Review

Friction stir welding (FSW) is established as one of the prominent welding techniques to join aluminium matrix composites (AMCs). It is a solid state welding process, takes place well below the melting temperature of the material, eliminates the detrimental effects of conventional fusion welding process. Although the process is capable to join AMCs, challenges are still open that need to be fulfill to widen its applications. This paper gives the outline of the friction stir welding technique used to join AMCs. Effect of process variables on the microstructure and mechanical properties of the joints, behavior of reinforcing materials during welding, effect of tool profiles on the joint strength are discussed in detail. Few improvements and direction for future research are also proposed.

A Study of Tool Wear and its Effect on the Mechanical Properties of Friction Stir Welded AA6092/17.5 Sicp Composite Material Joint

In most of the cases to weld AMCs friction stir welding is preferred than conventional welding process due to its specific advantages. But though there are advantages of welding AMCs by FSW the wear of tool material at the time of welding may become the major limitation of the process. The current experimental work is mainly focused on the study of tool wear and its effect mechanical properties of the weld joint. The workpiece plate used in this work is AA6092/17.5 SiCp composite material of 6.3 mm thickness. The FSW tool is made of H13 tool steel material with taper cylindrical pin geometry. Three sets of welding were done with varying tool rotational speed of 1000 rpm, 1500 rpm and 2000 rpm, keeping traverse speed fixed at 2mm/sec and toot tilt angle at 2°. The result shows that at 2000 rpm the tool wear phenomenon is very much prominent compared to other two rotational speeds. EDS analysis shows the presence of Fe particles in the nugget zone. From the microhardness graph, it has been observed that the hardness of nugget zone of the sample welded in 2000 rpm shows the higher value of hardness compares to the other joints due to the presence of Fe particle in nugget zone. It has been also observed from the tensile testing that the tensile properties of the sample welded at 2000 rpm show the minimum values. It can be recommended from the current study that the particular type of material can be weld by FSW with the current tool material and design within a tool rotational range of 1000-1500 rpm to obtain the better result.

Fatigue life estimations of alclad AA2024-T3 friction stir clinch joints

Joining alclad AA2024-T3 sheets is difficult for conventional welding processes due to ductile surface cladding layers. Friction stir clinching (FSC) was therefore proposed to overcome this problem. Here, two types of specimens, tensile-shear and cross-tension, were made to investigate general fatigue behavior of FSC joints. Critical fatigue cracks and failure modes were identified by photos and micrographs. Interfacial and kinked crack fatigue models consist of local and global stress intensity factors (SIFs) and a Paris law approach were taken for fatigue life estimations. The fatigue life estimations well agreed with the experimental fatigue data. The fatigue data of FSC joints in above specimens were well correlated by effective SIF ranges.

Evaluation of the Effect of the Water in the Contact Tip on Arc Stability and Weld Bead Geometry in Underwater Wet FCAW

Abstract: Underwater wet flux cored arc welding – FCAW – is an important process employed to repair marine structures with the advantages of not handling the components off the water and offers higher productivity in comparison to other conventional welding process. Under the water, wet welding activities are performed with lower stability, due to the pressure of the water surrounding the arc column and the presence of water in the gap between the contact tip and the electrode, which promotes poor electrical contact. In the present work, to compare the process stability of underwater wet FCAW with self-shielded electrode, welds were carried out using a special torch, which keeps the contact tip dry under the water. A two-level factorial design was used for experimentation and an Analysis of Variance was conducted to validate the results. Current coefficient of variation was used as the stability index. Welds performed with the torch have shown better-shaped beads and more stable arc in comparison to beads deposited with no mechanical barrier between water and the contact tip.

Experimental investigations of tungsten inert gas assisted friction stir welding of pure copper plates

Welding copper and its alloys is usually difficult to join by conventional fusion welding processes because of high thermal diffusivity of the copper, alloying elements, necessity of using a shielding gas and a clean surface. To overcome this inconvenience, Friction Stir Welding (FSW), a solid state joining process that relies on frictional heating and plastic deformation, is used as a feasible welding process. In order to achieve an increased welding speed and a reduction in tool wear, this process is assisted by another one (WIG) which generates and adds heat to the process. The aim of this paper is to identify the influence of the additional heat on the process parameters and on the welding joint properties (distribution of the temperature, hardness and roughness). The research includes two experiments for the FSW process and one experiment for tungsten inert gas assisted FSW process. The outcomes of the investigation are compared and analysed for both welding variants. Adding a supplementary heat source, the plates are preheated and are obtain some advantages such as reduced forces used in process and FSW tool wear, faster and better plasticization of the material, increased welding speed and a proper weld quality.

Experimental investigation of in-process mitigation of welding distortion for stainless steel plate using air-atomized mist cooling

In this study, welding-induced out-of-plane distortion of stainless steel sheets is examined in the case of applying air-atomized mist jet on the rear side of the weld pool. An internally mixed type air atomizing spray nozzle is attached to the welding torch and both are moved at the same speed and direction onto the welding centerline. The test specimens are 2 mm thick grade 304 stainless steel plates. Bead-on-plate welds are made on the plates using a DC Gas tungsten arc welding (GTAW) process. The measured welding distortion and residual stresses are compared with those of a conventional GTAW welding process. The experimental results show that the welds performed with a trailing heat sink using air-atomized mist have almost zero out-of-plane distortion. In addition, a slight welding residual stress reduction is achieved.

Status of India-specific Reduced Activation Ferritic-Martensitic steel and fabrication technologies development for LLCB TBM

India is developing the Lead Lithium Ceramic Breeder Test Blanket Module (LLCB TBM) for in-situ experiments in ITER. India-specific Reduced Activation Ferritic-Martensitic (IN-RAFM) steel is the chosen structural material for the fabrication of LLCB TBM. IN-RAFM steel plates with different thickness are being produced from commercial heats. Presently, characterization for mechanical and physical properties is in progress in order to generate material properties database from these commercial heats.In order to avoid welds on plasma facing surface of TBM First Wall (FW), scaled down mock-ups of FW are being fabricated using Hot Isostatic Pressing (HIP). Electron Beam (EB) welding, Laser/laser-hybrid welding and Narrow Gap-Tungsten Inert Gas (NG-TIG) welding, are being developed for fabrication of other TBM components. These welding processes have distinct advantage over conventional welding processes because of their high depth to width ratio, minimal HAZ, lower weld volume, reduced distortion and lower residual stresses in the weld joints. Mock-ups of LLCB TBM components are being fabricated using Grade 91/IN-RAFM steel to investigate the accessibility for the envisaged welding processes and to identify and develop the non-destructive evaluation (NDE) techniques. In addition, this would also help to establish the assembly sequence of LLCB TBM. Ultrasonic based methodologies are under development to assure integrity of these joints in the fabricated components.Details of these developments in IN-RAFM steel as structural material, fabrication technologies and mock-ups fabrication towards realization of the LLCB TBM are discussed in this paper.

Analysis of defects in clean fabrication process of friction stir welding

Striving for cleaner production is a sought-after manufacturing philosophy. Friction stir welding (FSW) is a joining technique with par excellence and far less invasive to the environment than even best conventional welding processes. It is energy efficient and free from consumables, affluent and radiations. It is, thus, accepted as a clean welding process that can produce acceptable quality joints. It suffers from some major challenges of defects of its own kind that subject the process open to improvements so as to prove itself a reliable production process. This study presents a holistic characterization of defects commonly found in FSW joints. The finding of the present study reveals that most defects are caused by inadequate heat generation, improper material movement around the pin and inadequate material consolidation behind the pin. The amount of heat generation and material stirring depends on several FSW parameters which may lead to the defect formation, if not selected properly. The results reported in this work are derived from sound literature support and experimentation. Prescriptions are made in the form of characteristics of defects such as likelihood of their location, main responsible parameters along with the recommendations for minimizing them.

Fatigue crack growth in Al-Zn-Mg (7075-T651) welds obtained by modified indirect and gas metal arc welding techniques

The modified indirect electric arc welding (MIEA) and the conventional gas metal arc welding (GMAW) processes were used to weld 7075-T651 aluminum alloy plates. The fatigue life behavior was studied for three different zones in the welded joints (base metal, heat affected zone and weld metal). Compact-type (CT) specimens manufactured from the 7075-T651 aluminum alloy welded plates were subjected to fatigue tests with constant amplitude cyclic loading. The CT specimens corresponding to MIEA weld metal shown the largest fatigue life (number of cycles to reach the stable crack propagation), which was four times larger than the weld metal obtained by GMAW. This improvement was attributed to the high tensile residual stresses induced by the application of three welding beads of the GMAW process in contrast with the stresses induced by the application of only one welding bead in the MIEA. The tensile residual stresses were of no consequence in terms of fatigue life for the heat affected zone (HAZ). At this zone, the microstructural transformation (soft zone formation in the HAZ) induces a similar fatigue life behavior. For the weld metal produced by the MIEA welding process, the fatigue crack growth tends to increase in comparison with the GMAW, whereas for the HAZ no difference was detected. Fracture surfaces of all materials were analyzed by using scanning electron microscopy to correlate the fatigue crack growth condition with the striations formation.

Friction stir clinching of alclad AA2024-T3 sheets

In order to improve corrosion resistance, alclad aluminum sheets, which are formed from pure aluminum surface layers cladded on high-strength aluminum alloy core sheets, are widely used in industry. However, in the conventional welding process, the alclad layer on the faying surface is a tough barrier, which significantly reduces weld strength. Therefore, friction stir clinching (FSC), a variant of friction stir spot welding (FSSW), was developed for joining alclad AA2024-T3 sheets. In this study, a FSC tool with a flat shoulder and a smooth probe, and a FSC die with a grooved circular cavity were used to make joints. The effects of important processing parameters on the mechanical performance of FSC joints were studied. A set of valid processing parameters was obtained. Untested and tested FSC joints were then examined using optical micrographs. The results indicated that the mechanical interlock and alclad layer shape of FSC joints are strongly correlated with their fracture and fatigue performance. Finally, a comparison with the mechanical performance of solid rivets and swept friction stir spot welds (swept-FSSWs) confirmed the feasibility of the FSC process for alclad aluminum sheets.

Application of Color Metallography to Study the Microstructure of Friction Stir-Welded Dual-Phase Brass Using Various Etchants

Brass is difficult to join using conventional fusion welding processes due to the loss of zinc during fusion. The relatively new friction stir welding (FSW) is a promising process to join brass without loss of zinc. The aim of the present work is to join 6-mm-thick Cu–38.55Zn brass using FSW and investigate the microstructure using color metallography. Two color etchants, namely Beraha 13a and Beraha 12a, were used to reveal the microstructure. The welded joints showed various zones due to the application of frictional heat and severe plastic deformation. The microstructure of heat affected zone was identical to that of base metal. The weld zone consisted of fine equiaxed grains due to dynamic recrystallization. Partial crystallization was observed along the thickness direction in the weld zone. The micrographs obtained using Beraha 12a etchant were better to that of Beraha 13a etchant.

Friction stir welded AM50 and AZ31 Mg alloys: Microstructural evolution and improved corrosion resistance

One of the major drawbacks of Mg alloys is poor weldability, caused by porosity formation during conventional fusion welding processes. Friction Stir Welding (FSW) is promising technique in this context since it is a solid state technique. Contradicting results were published in the literature regarding the FSWed Mg alloys joint's properties. Current research was performed in order to investigate the microstructure and corrosion properties of FSWed Mg alloys, studying representatives of two commercial families: wrought AZ31-H24 and die cast AM50. It was found that in both alloys recrystallization occurred during the FSW. In AM50 the mechanism of the recrystallization was continuous, manifested by dislocation rearrangement into sub grain boundaries. In AZ31 discontinuous recrystallization had occurred through grain boundaries migration - twins rotated with respect to the matrix, turning into low angle grain boundaries. Corrosion resistance has improved during the FSW in both alloys to different extents. In the AM50 alloy, the nugget exhibited significantly higher surface potential than the base metal mainly due to the higher Al concentration in the matrix of the nugget, resulting from the dissolution of Al-enrichment and β-Mg17Al12 phase. In the AZ31 alloy, no change in Al concentration had occurred, and the surface potential measured in the nugget was only slightly higher than in the base metal. These results underline the appropriateness of the FSW for Mg alloys since during the conventional welding deterioration of the corrosion resistance occurs.

Applicability of Friction Stir Welding to steels

significant developments in joining technology to emerge in the last 30 years. The technique has originally been developed for joining difficult-to-fusion-weld Al-alloys, particularly for high strength grades and now widely used in various industrial applications, such as transport industries. On the other hand, the application of FSW to high temperature materials such as steels is hindered due to the problems associated with the stirring tools although there is a wide interest for the application of this technique to these materials. Design/methodology/approach: The aim of this review is to address the current state-of-the-art of FSW of steels, focusing particularly on microstructural aspects and the resulting properties of these joints and discuss the future prospects of this technique for steels. For instance, the use of FSW can be advantageous for joining steels in some special applications where conventional fusion welding processes fail to produce sound cost effective joints, and the high tooling costs of FSW can be justified (i.e. underwater joining of steel pipes or hot plate welding in steel mills). In this study, only structural steels (mainly plain C steels), ferritic stainless steels, austenitic stainless steels and duplex stainless steels will be considered and the other types of steels are out of the scope of this work although some examples are included in the discussion. Research limitations/implications: The tools experience high temperatures in FSW of steels, i.e., above 1000°C. The number of tool materials which can withstand such temperatures is very limited. In addition, the welding of many common steels can be readily conducted by various conventional fusion welding methods. These joining methods are very flexible, easy-to-perform and well established in industrial applications, which further prevents the application of FSW to these materials. These limitations are to be overcome for commercial exploitation of this technique for joining steels.

Comparison of Wettability of Beads in MIG Welding Process with Duplex Current Feeding and Conventional MIG Welding Process

Comparison of Wettability of Beads in MIG Welding Process with Duplex Current Feeding and Conventional MIG Welding Process

Mechanical Behaviour Of Friction Stir Welding On Aluminium Based Composite Material

Friction-stir welding (FSW) is a solid-state joining process (meaning the metal is not melted during the process) and is used for applications where the original metal characteristics must remain unchanged as far as possible. This process is primarily used on aluminium and most often on large pieces which cannot be easily heat treated post weld to recover temper characteristics. The rotating tool “stirs” the material, softened by the frictional heat generated, and consolidates the stirred material behind the tool. This process has several advantages when compared to conventional fusion welding process. The present paper introduces the welding process and the welding of metal matrix composites. The welding was carried out on a CNC milling machine that was adopted for this work. Under Experimental condition of the study, mechanical strength, maximum temperature between the edge of the stir zone and the top surface, and effect of force against the tools are investigated. The micro hardness was also found to slightly increase with increased feed rate of the tool.

Crack risk in Nd: YAG laser welding of Ti-6Al-4V alloy

The excellent properties of titanium and titanium alloys, including corrosion resistance, high strength to weight ratio and high operating temperature, have led to their successful application in various fields. However, titanium and its alloys are destroyed by the conventional welding process if welding parameters are not controlled. Laser welding is one of the most reliable methods for use with titanium alloys because of its precision and rapid processing capability. In addition, it enables control of the welding parameters and their effects. In this study, Ti-6Al-4V alloy sheets were welded by Nd: YAG pulsed laser and the potential crack risk on the weld joints was investigated. The optimum results obtained in 3.9kW peak power, better ductility was obtained from the Grade 1 titanium alloy filling material.

The Interface Morphology of Thixo-Joined Dissimilar Steels

In many circumstances, a high quality joint of dissimilar metals can be hardly achieved by conventional welding process. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. The differences of two dissimilar steels at the test temperature on microstructural developments across the interface joint area were investigated. After Thixo-Joining, Interfacial microstructures were examined by optical microscope and scanning electron microscope (SEM) equipped with EDS (energy dispersive spectroscopy) in order to verify the interface welded area during the joining process while X-ray phase analysis was performed to identify the phase evolution and the type of carbides. The experimental results showed that at 1300°C a full penetration welded joint can also be clearly seen, whereby the base metal (D2 tool steel) is connected to the insert metal (304 stainless steel) along the bonding boundary to achieve what appears to be a perfect joining at the interfaces of both metals.

Advances and Potentials in Friction Stir Welding of Aluminum Alloys

Within the last decade, Friction Stir Welding (FSW) has increasingly been gaining relevance for joining nonferrous metals, especially aluminum alloys. Possible applications range from the aerospace and automotive sector up to manufacturing electrical components. Compared to conventional fusion welding processes, FSW offers numerous advantages, as it for example does not require shielding gas or filler material. However, FSW is still not applied or taken into account during the product development process in proportion to its potential. This is mainly caused by the lack of data in order to evaluate the process economically and differentiate it to other processes like arc and laser welding, also regarding technological factors. Therefore, this investigation focusses on the possibilities and limits when joining wrought and cast aluminum alloys, like EN AW-6082 T6, EN AW-7075 T651 and AlSi11Mg0,3, respectively, by FSW compared to MIG. The weld quality of the samples is characterized by tensile testing, hardness measurements and microstructure analysis. Furthermore, an approach to reduce the process forces by using FSW tools with reduced diameters and respectively adjusted process parameters is presented.

Friction stir vibration welding process: modified version of friction stir welding process

In the current research, a new method is applied to modify the conventional friction stir welding (FSW) process. Fixture, which fixes the workpieces, is shaken mechanically during FSW in a direction normal to weld line in order to increase the straining of weld region material. In other words, vibration of workpieces is accompanied by the rotating motion of tool. This new process can be described as friction stir vibration welding (FSVW). Al 5052 alloy specimens are welded by two welding methods, FSW and FSVW. Microstructure and mechanical properties of welded specimens are compared. Metallography analyses indicate that grain size decreases and hardness increases as FSVW method is applied. Tensile test results also show that strength and ductility values of friction stir vibration (FSV)-welded specimens are greater than those relating to friction stir (FS)-welded specimens. It is because of more work hardening of plasticized material, during FSVW, which leads to more generation and movement of dislocations. Correspondingly, grain size decreases and mechanical properties improve. Additionally, it is observed that the mechanical properties of the weld improve as vibration frequency increases.