Lower Tool Rotational Speed Research Articles

Friction Stir-Spot Welding of AA5052-H32 Alloy Sheets: Effects of Dwell Time on Mechanical Properties and Microstructural Evolution

Friction stir-spot welding (FSSW) as a solid-state joining process for local welding offers a number of benefits for applications in the automotive, aerospace, and marine industries. In these industries, and from an economic point of view, producing spot welds at a low rotating speed and in a short time is critical for saving energy and enhancing productivity. This investigation helped fill a knowledge gap in the literature about FSSW of 4 mm similar lap joints of AA5052-H32 sheet materials, in which welding takes place over a short time period with a slow tool rotation speed. Consequently, the purpose of this work was to investigate the feasibility of FSSW 2 mm thick AA5052-H32 aluminum alloy sheets to produce 4 mm thick similar spot lap joints at various low dwell times of 1, 2, and 3 s and a constant relatively low tool rotation speed of 500 rpm. The introduced heat input for the friction stir-spot welded (FSSWed) lap joints was calculated based on the applied processing parameters. Joint appearance, cross-section macrostructures, and microstructure features of all the spot welds were evaluated. The mechanical properties (hardness contour maps and maximum tensile shear loads) were also examined. The results show that joining 2 mm sheet thickness AA5052-H32 at a low heat input in defect-free similar lap joints could be successfully achieved. The stir zone (SZ) region became wider as the dwell time increased from 1 to 3 s. The hardness value of the SZ was higher than that attained by the AA5052-H32 base material (BM) for all applied dwell times. Especially at 2 s, the hardness of the SZ was approximately 48% higher than that of the BM. This increase in hardness may be attributed to the high grain refinement of the new dynamically recrystallized grain (4 µm) in the SZ compared to the cold-rolled BM grain size (40 µm). Among the tried FSSW process variables, the dwell time of 2 s at a rotation rate of 500 rpm also produced the maximum tensile shear load of 4330 N. Finally, the locations and features of the fracture surfaces of the FSSWed joints were examined using a scanning electron microscope (SEM) and the obtained results were discussed.

Welding Investigation on AA6063-T6 Aluminium alloy during Friction Stir Welding process

The Friction stir welding (FSW) is widely used to weld aluminium alloy for industrial applications such as shipbuilding, aerospace and automobile due to its lighter weight and high strength. The current work is carried out to examine the different process parameters to weld AA6063-T6 aluminum alloy with FSW process. The tool rotation speed, feed, plunging depth and dwell time are considered as the welding parameter. The three test coupons have been welded at three different rotational speeds. The tensile strength and hardness at the weld vary with the speed of rotation of the tool. The higher tensile strength is achieved at lower tool rotational speed. The tensile strength achieved at 1000rpm and 1400rpm is 191Mpa and 131rpm respectively. The higher strength is achieved due to the refinement of grains and recrystallization in stirred zone. The microstructure test confirms the presence of uniformly fine grains at weld area and equiaxed grains at HAZ region.

Effect of tool rotation speed on microstructure and mechanical properties of underwater friction stir welding 6061 aluminium alloy

This work presents the experimental investigation of the effect of tool rotation speed (TRS) on the mechanical properties of the 6061-T6 aluminium alloy weld joint in the underwater friction stir welding (UFSW) process. The experiments are conducted with four different TRS, 710, 900, 1120, and 1400 rpm, and a constant welding speed (WS) of 20 mm/min, respectively. The welding is performed under the water in the butt joint configuration on the vertical milling machine (Model HMT FN2H). The experimental result shows that the average grain size decreases and tensile strength and hardness increases on increasing the TRS up to mid-range of the TRS and further increasing the TRS the trend of grain size and tensile strength and hardness are increases and decreases, respectively. The maximum tensile strength value is 190 MPa, and the minimum grain size is 5 µm at 1120 rpm. Additionally, the optimum condition of tensile strength and weld zone shape is compared with the conventional friction stir welding process, and it is found that tensile strength is increased by 20% and smaller weld zone shape are observed in underwater friction stir welding process. The brittle fracture dominance is observed at lower TRS and ductile dominance fracture in 900, 1120, and 1400 rpm of the weld joint.

Influence of Tool pin Profiles in Friction Stir Welding of Aluminum Alloy and Polycarbonate

In this study, the impact of tool pin profile on the dissimilar joining characteristics of aluminum alloy AA2017 and polycarbonate in friction stir welding (FSW) was examined. The tool pins made of SKD11 tool steel were used in the experiments of the FSW to join AA2017 and polycarbonate plates in a butt configuration at a tool rotation speed of 1320 and 1760 rpm and tool transverse speed of 60 mm/min. The tool shoulder diameter and tool pin height were set to 10 mm and 2 mm. The shapes of tool pin were cylindrical with and without groove, tapered cylindrical with and without groove, bobbin shaped with and without groove, square, triangular, pentagonal, hexagonal, oval, and ellipsoidal. The measurement of axial force was performed using a dynamometer. The changes in workpiece temperature at six locations during the process were measured using K-type thermocouples embedded in the plates. Microstructures of welded joints were examined by an optical microscope. Vickers Microhardness mapping was performed in and around the weld nugget zone, which is formed by the material flow between the two different base materials. From the result, the grooved tool pins generated less heat; while cylindrical, square, and oval type pins are also result in the superior properties of the welds during joining processes. Each tool pin had unique material flow behavior and weld formation, and the weld defects such as tunnel/voids occurred at the joint interface. The oval tool pin gives rise to the highest joint efficiency at a higher tool rotation speed, and the ellipsoidal tool pin generates the highest joint efficiency at a lower tool rotation speed was noticed.

Degradation of nickel-bonded tungsten carbide tools in friction stir welding of high carbon steel

Rapid tool degradation poses a critical challenge for joining of high carbon steels using friction stir welding (FSW) despite its ability to provide sound and defect-free welded joints. Tools of tungsten carbide with nickel binder phase (WC-Ni) are potential alternatives as they exhibit good strength and toughness. A detailed examination on the wear and consequent damage of WC-Ni tools for FSW of steels is reported in this work. The results show that the longevity of the WC-Ni tools is improved at relatively higher welding speed and lower tool rotational speed during FSW of high carbon steels. In contrast, higher tool rotational speeds and lower welding speeds result in higher rate of heat generation and elevated temperature leading to adhesion wear and oxidation of the tools. In FSW of typical 3-mm-thick high carbon steel plates, a tool rotational speed of 300 rpm and welding speed of 150 mm min−1 resulted in the minimum tool wear and allowed the use of a single tool up to 1000 mm without any significant damage.

Review and Feasibility Study on Micro Friction Stir Welding of Al/Fe Butt Joints

In the automobile industry, there is an increasing demand for Al/Fe dissimilar metal joining. Friction stir welding (FSW) is an efficient solid-state welding method to achieve high-quality Al/Fe dissimilar metal welding. Here, we reviewed the previous studies on butt FSW of thin Al/Fe sheets and conducted feasibility tests to investigate the applicability of micro FSW with a base material thickness of 1 mm or less. Most of the past literature, except for one study that adopted 1.12 mm-thick specimens, has worked with a base metal thickness of 1.5 mm or more. Selecting appropriate parameters can lead to a weld strength that is more than 90% of the base metal strength. Through feasibility tests on 2 mm-thick specimens, we could derive the welding conditions to obtain sound welds and the required joint strength. An adequate range (0.5-0.75 mm/rev) of advance per revolution was recommended to ensure the weld strength. A feasibility test on 1 mm-thick specimens revealed the possibility of melting of Al base metal during FSW of 1 mm-thin sheets; moreover, a low tool rotation speed was found to be crucial in ensuring the weld joint strength. The maximum weld strength for 1 mm-thick specimens was 200 MPa, which is 117% of the required weld strength. Key words: Dissimilar metal welding, Aluminum alloy, Steel, Micro friction stir welding, Joint strength

Hybrid Friction Diffusion Bonding of Tube–Tubesheet Joint: A finite Element Model

A three-dimensional finite element model for hybrid friction diffusion bonding of tube–tubesheet joints is developed based on coupled Eulerian–Lagrangian technique. The investigation is aimed to study the effect of process parameters on temperature and pressure buildup in addition to material flow during the process. Temperature-dependent material properties were utilized in addition to Johnson–Cook material flow-stress model to describe the material behavior, while modified Coulomb’s frictional model was used to govern the contact between the tool and the workpiece. The numerical findings show good agreement with early experimental results. Lower tool rotational speed and longer welding time may lead to uniform tube deformation. Estimated temperatures and pressures could serve as key indicators for the diffusion bonding to take place or not.

Effect of post weld heat treatment and welding parameters on mechanical and corrosion characteristics of friction stir welded aluminium alloy AA2014-T6

This paper addresses the effect of post weld heat treatment methods on the mechanical and corrosion characteristics of friction stir welded aluminum alloy AA2014-T6. Aluminum alloy AA2014 is mainly used in applications that demand high strength to weight ratios, such as aerospace, marine, and industrial applications. In this work, AA2014-T6 plates of 6 mm thick were butt welded using a tool with a square profile. Tensile strength, hardness, and corrosion characteristics were compared between the samples as welded and post weld heat treated. Welded samples that were heat treated for a shorter ageing period (8 h) showed improved tensile strength irrespective of welding process parameters, compared to as-welded samples. The samples heat treated for a longer ageing period (9 h) showed a decline in tensile strength for low tool rotation speed. Hardness increased in welded samples heat treated for 8 h. Welded samples heat treated for 9 h show high passivity in corrosion media.

AA5052 sheets welded by protrusion friction stir spot welding: High mechanical performance with considering sheets thickness at low dwelling time and tool rotation speed

In the present work, AA5052 sheets with thickness of 1 mm were successfully welded by protrusion friction stir spot welding as a low cost single-step method with a simple design that produces the no-keyhole joints with special mechanical properties at short dwell time and low tool rotation speed. By using suitable process parameters, the process is able to produce welds with superior mechanical performance in items of peak load and energy absorption compared to other techniques. The plunging depth and dwell time in this method were set as 0.2 mm and 6 s, respectively. The tool rotation speed was changed as 500, 800, 1250, and 1600 r/min to determine the optimum condition based on the microstructural and mechanical properties. Welds strength produced by the protrusion friction stir spot welding was directly related to the joint thickness, and the effective thickness of the upper sheet was maximum at 500 r/min. Protrusion friction stir spot welding joints presented circumferential failure mode after tensile shear testing. Regarding the sheets thickness used in this study, the joints produced by the current work presented high load bearing ability at dwell time of 6 s and tool rotation speed of 500 r/min compared to other techniques.

Effect of the processing parameters of friction stir processing on the microstructure and mechanical properties of 6063 aluminum alloy

After friction stir processing (FSP), fine equiaxed α-Al grains formed in the weld nugget (WN) of 6063 Al alloy, and their size increased with increasing tool rotation speed in the range of 300–700 rpm. The grain sizes in the bottom zones were smaller than those in the upper zones in the WN, and two-pass FSP led to a larger grain size than single-pass FSP. Tunnel defects can be observed in the thermomechanically affected zone (TMAZ) for a low tool rotation speed of 300 rpm. When the rotation speed exceeds 700 rpm, a good combination interface can form between the WN and the TMAZ. Electron backscatter diffraction (EBSD) results showed that the fraction of the high-angle grain boundary (HAB) was obviously increased after FSP in the WN. The alloys exhibited a more concentrated distribution and higher densities. Transmission electron microscopy (TEM) analysis results showed that the densities of needle-shaped precipitates were reduced in the WN. Some high-density dislocation pile-ups formed at some grains. The ultimate tensile strengths (UTSs) were lower than that of the base material (BM) at lower tool rotation speeds for both single- and two-pass FSP. With increasing speed, the UTSs increased gradually and then became higher than that of the BM. The strain values were all lower than that of the BM.

Effect of Friction Stir Welding Parameters on Mechanical Properties and Microstructure of AA2195 Al–Li Alloy Welds

In this paper, effect of friction stir welding process parameters on mechanical properties and microstructure of AA2195 welds were studied. Five levels of tool rotation speed from 400 to 1000 rpm and three levels of travel speed from 100 to 300 mm/min were considered. These parameters affected heat input generation in the welds, thereby influencing stir zone geometry, grain size evolution in stir zone, tensile properties and hardness of the weld. Low tool rotation speed and high travel speed resulted in finer grain size. Travel speed significantly affected the tensile properties compared to rotation speed. Processing window to achieve defect-free welds was identified, and maximum weld efficiency was obtained at 400 rpm rotation speed and 300 mm/min travel speed.

Effect of Various Welding Parameters on Corrosion Behavior of Friction-Stir-Welded AA 7075-T651 Alloys

The 7000 series aluminum alloys provide the highest strength of all aluminum alloys and are widely used in the aerospace industries. They are practically unweldable by conventional fusion welding techniques. Friction stir welding is a widely accepted process to join this material. The paper intends to evaluate the electrochemical behavior of friction-stir-welded AA 7075-T651 alloy under varying welding conditions. An attempt has been made to evaluate the effect of tool rotation speed, welding speed, and shoulder diameter on its corrosion characteristics. The temperature histories during welding were continuously recorded with the help of thermocouples. The corrosion characteristics have been examined as per ASTM G-34 standards. The analysis is done by immersing the plates in EXCO solution and analyzing through optical imaging, SEM and TEM. The analysis revealed that the heat-affected zone was found to be most susceptible to corrosion. The corrosion resistance is found in the order—weld nugget > unwelded base metal > HAZ. The experiments revealed that the corrosion resistance of the welded plates is directly proportional to the heat input during the welding process. The plates welded with lower tool rotation speed, higher welding speed, and lower shoulder diameter exhibited higher corrosion resistance.

Surface modification of Al6061 by graphene impregnation through a powder metallurgy assisted friction surfacing

Impregnation and homogeneous distribution of nanomaterials on metallic surfaces have always been a challenge for researchers in recent times. In the present work, authors demonstrate a surface modification of Aluminium by graphene impregnation through a novel powder metallurgy assisted friction surfacing (PMAFS) process. This modified friction surfacing technique involves two stages. In the first stage, an Aluminium-graphene composite tool is fabricated through a powder metallurgy route. In the second stage, this consumable tool is utilized for FS to obtain a composite coating layer on Aluminium surface. Experimental results show that the surface composite prepared by this modified friction surfacing technique does have impregnated graphene successfully in Al matrix. The obtained surface composites were characterized by using SEM, TEM, and XRD. Morphology and damage to graphene are studied by using Raman spectroscopy. Nanoindentation study was conducted for a various set of processing parameters with variation in graphene content. Further, the influence of graphene percentage and processing parameters on mechanical properties and microstructural changes were also studied. Composites prepared at relatively lower tool rotational speed with low content of graphene in the tool is found to have optimum mechanical properties with a homogeneous distribution of graphene in Al substrate. The nano-hardness of the surface composite is increased by 100% after impregnation of graphene nano platelets (GNP) with an optimum set of parameters.

Friction stir forming of dissimilar grade aluminum alloys: Influence of tool rotational speed on the joint evolution, mechanical performance, and failure modes

Friction stir forming (FSF) is a solid-state, eco-friendly spot welding technique primarily applied for lap joining dissimilar sheet metals. The details related to the process are scarce in literature. The present work explores the potential of the FSF process for joining dissimilar grade alloys of same metal, namely aluminum. The effect of tool rotational speed on the joint formation and mechanical performance of FSF joints between AA5052-H32 and AA 6061-T6 sheets is studied through systematic experimentation and macrostructure analysis. Hardness distribution across the joint, joint morphology, and failure modes at varying rotational speeds are also presented. The tool rotational speed shows significant effect on the mechanical performance results, zones formed within the joint, and hardness distribution across the joint. Maximum lap shear strength, about 6 kN, obtained in the present work is superior than that of joints fabricated on same material combination with other friction-based joining technologies. The lower and medium tool rotational speeds, between 500 and 1500 rpm, are the best choices for fabricating FSF joints for the materials used. Macrostructure analysis revealed that at lower tool rotational speed ( 1500 rpm), localized stir zones are distributed over the cross-section. Friction stir form samples showed an inverted “W”-shaped hardness profile over the cross-section, and the joint morphological features are independent of the tool rotational speed. Failure modes such as partial bond delamination, tear-off, and pull-out occur randomly and have no systematic correlation with the tool rotational speed.

Microstructure and wear behavior of friction stir processed cast hypereutectic aluminum silicon

Hypereutectic as-cast Al-18Si-Cu-Ni alloy was subjected to friction stir processing (FSP). The resultant effect of FSP on the alloy was evaluated by microstructure analysis and wear tests (dry sliding). A significant microstructural modification and enhancement in wear behavior of Al-18Si-Cu-Ni alloy was recorded after friction stir processing. Wear resistance improvement was related to considerable modification in size, morphology and distribution of silicon particles, and hardness improvement. It was found that lower tool rotation speed was more effective to refine silicon particles and in turn increase wear resistance. Minimum Si particle mean area of about 47.8 µm 2 , and wear rate of 0.0155 mg/m was achieved.

The weld interface for friction spot welded 5052 aluminium alloy

Friction Spot Welding (FSpW) is considered to be a competitive technique for producing high quality welds, especially in lightweight alloys. The geometric defects and features originating at the interface between the two welded sheets have an important influence on the mechanical performance of the joint. This work investigates the weld microstructure for FSpW in AA 5052 sheets produced using tool rotational speeds of 900, 1400 or 1900 rpm. OM and SEM were used to analyse the microstructural features of the weld. The mechanical performance was investigated using shear tensile testing, and the fracture mechanisms were assessed by SEM. Three distinct weld interfaces were observed and named as follows: primary bonding, partial bonding and secondary bonding. For welds processed at a lower tool rotational speed (900 rpm), the equivalent bonding ligament is increased, resulting in better joint mechanical performance.

Experimental failure study of friction stir spot welded similar and dissimilar aluminum alloys

In this paper, it has been presented that with macroscopic study of nugget and using “effective distance” (ED) index, the reason of different strength of joints, which are welded with different parameters and from different materials, can be explained. Welds that have longer ED carry more static lodes compared to others. ED is the linear distance of Hook tip, i.e., the separation point of two overlapped sheets in partially bounded region which is crack initiation point, and keyhole. It has presented that Hook tip geometry also is an important factor that affects joint strength. The zig-zag Hook tip type is present at high strength welds while straight Hook tip can be seen for low strength joints. Lower tool rotational speed and higher tool plunge rate result longer ED and higher shear strength. ED is shorter for joints that are welded from dissimilar alloys compared to similar ones and joint strength differs similarly. The highest shear strength was 3050 N which was obtained with specimen that was welded from similar 6063-T3 aluminum sheets with tool rotational speed of 800 rpm and tool plunge rate of 80 mm/min. For this specimen, effective distance was 2025 μm.

Fatigue crack paths and properties in A356-T6 aluminum alloy microstructurally modified by friction stir processing under different conditions

A356-T6 cast aluminum alloy is a light weight structural material, but fatigue crack initiates and propagates from a casting defect leading to final fracture. Thus it is important to eliminate casting defects. In this study, friction stir processing (FSP) was applied to A356-T6, in which rotating tool with probe and shoulder was plunged into the material and travels along the longitudinal direction to induce severe plastic deformation, resulting in the modification of microstructure. Two different processing conditions with low and high tool rotational speeds were tried and subsequently fully reversed fatigue tests were performed to investigate the effect of processing conditions on the crack initiation and propagation behavior. The fatigue strengths were successfully improved by both conditions due to the elimination of casting defects. But the lower tool rotational speed could further improve fatigue strength than the higher speed. EBSD analyses revealed that the higher tool rotational speed resulted in the severer texture having detrimental effects on fatigue crack initiation and propagation resistances.

An Improved FSW Tool for Joining Commercial Aluminum Plates

This paper presents the experimental findings of friction stir welding (FSW) on commercial aluminum plates of 6.5mm thickness using a newly developed improved flat pin tool with side radius and its comparison with standard straight threaded pin tool with flat collar made of hardened steel. The effect of FSW is studied on hardness, strength, toughness and microstructure with different tool rotational speeds ranging from 400rpm to 1400rpm, at a constant feed rate i.e., at 30mm/min for making comparison between the newly developed flat pin tool and the standard straight threaded pin tool. The comparative study indicates that, the newly developed tool produces the better tensile strength than the standard straight threaded tool in the entire range of the tool rotational speeds. The maximum strength of the FSW joints is 78% of that of its base metal at 400rpm using the new tool. It is further observed that, for both the tools, the hardness of weld zone is increased at lower tool rotational speed, while refined microstructure can be noticed on surface of the weld zone at higher tool rotational speed.

Mechanism investigation for the influence of tool rotation and laser surface texturing (LST) on formability in single point incremental forming

Single point incremental forming (SPIF) is a new sheet metal forming process which achieves higher formability, greater process flexibility and reduced forming force compared to conventional sheet forming operations due to its characteristic of localized deformation. In recent years, a novel SPIF process assisted by localized friction heat is developed to further improve the material formability. Physically, the frictional heat is generated by the high relative motion at tool–workpiece interface resulted from tool rotation. However, the mechanisms behind formability difference induced by tool rotation at both low and high speed ranges are required to investigate in detail. In this paper, a series of experiments with an increase of tool rotation speeds ranging from 0 to 7000rpm are conducted to form AA5052-H32 aluminum alloy sheets into a truncated funnel. Additionally, the obtained results are analyzed in terms of formability, forming forces and temperature trends to find out the different roles of friction and heat during the forming process. As a result, the formability behaviors at varying tool rotation speeds can be categorized into four stages according to different reasons. It indicates that friction is the dominant factor in low tool rotation speed range (0–1000rpm) but will be substituted by thermal effect and potential dynamic recrystallization in high tool rotation speed range (2000–7000rpm). Furthermore, due to the proved lubrication enhancement and hydrodynamic enhancement generated by surface textures, a laser surface textured forming tool is also utilized to show its influence on forming forces, measured temperatures and the corresponding formability. Finally, it demonstrates that the fabricated laser surface texturing (LST) is capable to reduce the friction at tool–workpiece interface and change the magnitude of heat generation.