Dissimilar Friction Stir Welding Research Articles

Microstructure evolution and fracture behavior of dissimilar friction stir welding of 1060Al alloy to AZ31B Mg alloy

In this paper, the microstructure evolution and fracture behavior of 1060 Al/AZ31B Mg dissimilar friction stir welded joints were investigated. Experimental results showed that dynamic recrystallization occurred in the nugget zone (NZ) and thermo-mechanically affected zone (TMAZ), and the grains were considerably refined. As the welding speed increased, the percentage of high angle grain boundaries (HAGBs) and the degree of recrystallization in the NZ gradually decreased, while the percentage of HAGBs and the degree of recrystallization in the Mg-side TMAZ first increased and then decreased. The NZ and Mg-side TMAZ possessed a strong {0001} basal texture, and the texture strength first increased and then decreased with increasing welding speed. When V = 30, 110, and 190 mm/min, the tensile strengths of the joints were 74 ± 2.2, 93 ± 3.3, and 80 ± 1.2 MPa, respectively. The joints showed two fracture modes: the joint fractured along the Mg-side TMAZ/NZ interface (mode I); the joint failed from the bottom of NZ and then fractured along the middle region between the NZ and Mg-side TMAZ (mode II). The grain size, texture distribution, and local dislocation concentration affected the fracture behavior of the joints. • The evolution of microstructure and fracture behavior of Al/Mg dissimilar FSWed joints were studied by EBSD. • Two fracture modes of the joints were found and discussed. • The fracture mechanism of the joints at different welding speeds was clarified.

The inhibitory effect of stir zone liquefaction and eutectic-phase formation on the growth of γ/β intermetallics during dissimilar FSW of Al/Mg alloys

Controlling the formation of intermetallic compounds (IMCs) is a critical issue in friction stir welding (FSW) of Aluminum (Al) to magnesium (Mg) alloys. During FSW, AlMg IMCs can form through two mechanisms comprising solid-state diffusion and liquefaction. Two kinds of IMCs can form during FSW of Al/Mg, Al3Mg2 (β) and Al12Mg17(γ). The IMCs produced via the former mechanism are identified as continuous whereas the IMCs produced by the latter typically appear as separate islands inside a matrix of eutectic structures. The present study aims to examine the impact of each morphology on the joint strength. For this purpose, dissimilar FSW of AA1050/AZ31 was carried out in lap configuration. The microstructure of the joints, as well as the fracture surfaces, were studied by scanning electron microscopy (SEM) and joint strength was evaluated by shear tensile testing. It was observed that the IMCs formed via diffusion were detrimental when their thickness exceeded 2 μm. It was also shown that liquefaction during FSW could control the thickness of the continuous IMCs layer. To elucidate this phenomenon, analytical and numerical methods were applied to calculate the growth kinetics of IMCs. It was concluded that the liquefaction phenomenon and the subsequent formation of eutectic structures reduced the activity of elements and thereupon hindered the diffusion rate in the solid state. In this case, although liquefaction raised the overall volume fraction of IMCs, the fracture load increased due to the propagated fracture through the eutectic microstructure rather than the continuous IMC layer.

A Study on Optimization of Welding Parameters and their Effect on Joint Properties of Dissimilar AA6082-T6 and AA7050-T7 Friction Stir Welds

A Study on Optimization of Welding Parameters and their Effect on Joint Properties of Dissimilar AA6082-T6 and AA7050-T7 Friction Stir Welds

Comparative Study Between Stainless Steel and Carbon Steel During Dissimilar Friction Stir Welding with Aluminum: Kinetics of Al–Fe Intermetallic Growth

Comparative Study Between Stainless Steel and Carbon Steel During Dissimilar Friction Stir Welding with Aluminum: Kinetics of Al–Fe Intermetallic Growth

Microstructural and Mechanical Behaviors of Friction Stir Welded Dissimilar AA6082-AA7075 Joints

In this research, microstructural events and mechanical behaviors in dissimilar friction stir welding (FSW) of aluminium (Al) alloy AA6082-AA7075 joints have been evaluated to apply aerospace, defense, and military sectors. FSW parametric effects have a more significant impact on the mechanical performances and microstructure of produced joints. FSW tool rotational speed, welding speed, and tool plunge speed were chosen to make the weld joints. The rotational tool speeds of 1600 rpm and 2300 rpm, welding speeds of 40 mm/min and 60 mm/min, and tool plunge speeds of 20 mm/min and 30 mm/min were set as the upper and lower limits. A constant axial force of 5 kN was maintained throughout the joint fabrication process. A taper pin-profiled tool was utilized to produce the butt welded joints. Mechanical properties of microhardness, tensile strength, yield strength, elongation, and bending strength of the joints were analyzed. The response of the stir zone microstructure to processing parameters was evaluated using optical microscopy (OM) and fractographic analysis of a tensile specimen shown by scanning electron microscope (SEM). The weld joints produced at 2300 rpm, tool traveling rate of 40 mm/min, and tool plunge speed of 30 mm/min showed the greatest tensile strength of the 191 MPa hardness of 145 Hv at the weld center and also the maximum bending strength of 114.23 N/mm2 was achieved. The lowest bending strength of 25.38 N/mm2 was obtained at 1600 rpm with 60 mm/min due to inappropriate mixing of the base metals and poor joint quality. Furthermore, this study revealed that a higher tool plunge speed facilitates the formation of equiaxed grains in the thermomechanically affected zone (TMAZ) on the advancing side (AS). Additionally, the increment in tool rotational speed significantly improved the tensile strength, weld joint quality, and joint efficiency.

Investigation of microstructural and mechanical properties of AA1050-AZ91D dissimilar friction stir welding

Joining of aluminium and magnesium alloys frequently pose significant challenges to the extent where joining may seem impossible, due to differences in the physical, metallurgical, and chemical properties of the materials. Friction stir welding is a solid-state welding technique which uses a non-consumable tool to join metals. This study examines the dissimilar friction stir welding of 3 mm thick AA1050 and AZ91D alloy sheets. Successful defect-free joints were achieved at rotational speeds of 400 rpm and 600 rpm, and a constant traverse speed of 50 mm/min. The metallurgical investigations used to characterize the microstructure of the welds are optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The microstructures of the samples show distinct morphology attributed to their different rotational speeds. However, Al3Mg2 intermetallics (IMCs) phase was detected in the white bands present in both weld samples. The IMCs were formed through solid-state diffusion. The mechanical properties characterizations includes the microhardness profiles and tensile testing. The variation in the rotational speeds do not have a significant effect on the microhardness distribution of the weld samples. The tensile strength of the dissimilar weld improved substantially with the presence of an interpenetration feature (IPF).

Part II.: Dissimilar friction stir welding of nickel titanium shape memory alloy to stainless steel – microstructure, mechanical and corrosion behavior

In the present work, nickel-titanium (NiTi) shape memory alloys (SMAs) is joined to 304 stainless steel (SS) using friction stir welding (FSW) using process parameters of 400 rpm and a constant tool translation speed of 75 mm/min. The macrostructure of the dissimilar weld showed some surface tunneling defects but there were regions of the weld that were defect free and without evidence of intermetallics at the interface. The weld stir zone (SZ) showed grain refinement compared to both base materials (BM). NiTi side of the joint showed very fine thermomechanical affected zone (TMAZ) and absence of a distinct heat affected (HAZ) zone, resulting in very little variation in microhardness. SS side of the weld showed typical FSW microstructural zones with higher microhardness in the SZ (270 HV) compared to BM (185 HV). Tensile testing of the weld showed a small initial plateau region, characteristic of shape memory alloys (SMAs) arising from NiTi part of the weld. Importantly, the transformation temperatures of NiTi, measured by differential scanning calorimetry (DSC) from different weld zones, varied by no more than 4 °C. Corrosion properties of the weld zone investigated in 3.5 wt. % NaCl solution showed moderately inferior corrosion resistance of dissimilar weld, compared to individual base metals, as characterized by the surface film impedance and corrosion current density. The decreased corrosion resistance was attributed to inhomogeneous passive film formed across the weld due to zonal heterogeneities. The predicted and measured galvanic parameters of the galvanically coupled base metals suggested that there appeared to be negligible galvanic effects. The results from the study show that with further development, FSW can be successfully utilized to create dissimilar joints between NiTi and stainless steel. • Nickel titanium shape memory alloy joined to stainless steel using friction stir welding process. • Refined grained along with absence of intermetallics was observed in the weld zone. • The transformation temperature on NiTi side across the different weld zones shows very little variation. • Under tensile loading, dissimilar joint showed small plateau region, characteristic of SMAs in martensitic phase. • Weld zone showed slightly inferior corrosion property compared to individual base material, while negligible galvanic effect was observed.

Microstructure and texture correlation of secondary heating assisted dissimilar friction stir welds of aluminum alloys

Present work aims to study the influence of secondary heating on material behavior during the friction stir welding (FSW) and examine it through the texture analysis. In the present context, the secondary heating pertains to the additional heat provided using a gas torch other than the heat primarily produced due to the process itself. Stop tool action technique is used to appraise the material flow around the pin. The material flow and evolution of textures during the process is studied by employing electron backscatter diffraction analysis. For analysis, the transverse sections of dissimilar FSW joints of AA6061-AA7075 and AA7075-AA2014 prepared with and without the application of secondary heating keeping the tool pin embedded in the joint are used. The basic assertions on strain rate based upon texture analysis and grain boundary engineering are used to explain the nature of material behavior during the process. The misorientation angle distribution is observed to shift towards random distribution for severe plastic deformation and additional heat supplied. Texture analysis reveals dominance of B/B‾ shear texture with sufficient C component in joints supplied with additional heating. For AA7075-AA2014 (without secondary heating) strong α-fiber is observed in the texture orientation distribution function plots. An equation is established to estimate the material volume flow around the pin in one revolution. The optical micrographs of welded joints prepared with and without use of secondary heating are compared to visualize the increase in material flow volume. The hardness of the joints obtained tend to decrease along the weld section on application of additional heat due to the dissolution of precipitates.

Review on dissimilar structures joints failure

Fuel economy has become, more than ever, one of the central keys around which the industrial development of transportation means (mainly aeronautics and aerospace) orbits around. In order to improve fuel consumption efficiency, lightweight and multipurpose dissimilar structures are pushing the boundaries of innovation through generative design, joining of dissimilar materials through innovative technologies and advanced manufacturing systems, such as addictive manufacturing. Friction Stir Welding (FSW) and Laser Beam Welding and their hybrid technologies represent some of the solid-state welding technologies that play significant roles in what concerns to join dissimilar materials such as Steels, Aluminum and Titanium alloys as well as high performance thermoplastics like Polyether Ether Ketone (PEEK) and Polyphenylene Sulphide (PPS). This article makes a review on the failure modes associated to dissimilar FSW joints, through a comprehensive analysis and enumeration of the different cases that are mentioned in the literature. Initially, it will be reviewed the state of the art related to the technological processes and materials categorization, as well as a summary of several papers and the respective reported failure modes, organized by static strength and defects, fatigue behavior and crack growth, and corrosion proneness and corrosion cracking.

Performance characteristics optimization in dissimilar friction stir welding using Grey relational analysis

In the present work, Friction stir welding of dissimilar materials AA5083 & AA6061 is carried out and by using Taguchi-based Grey Relational Analysis. The output characteristics like tensile strength, elongation, and hardness values are investigated using response surface methodology and grey relational analysis. The quality of the welded joint is measured based on the experimental values of tensile strength, elongation, and hardness of the joint the experiments were conducted in accordance with the L9 orthogonal array assigning different levels values to the process parameters. Tool pin profile, rotational speed, welding speed, and tool tilt angle are selected as the significant input parameters. Analysis of variance (ANOVA) is used to analyze the effect of each input welding parameter on the output responses. Statistical results show that the results of the confirmatory experiments are within 95% confidence optimal conditions with smaller deviations.

Effects of Welding Parameter on Atom‐Scale Interfacial Diffusion Behavior of Al/Cu Dissimilar Friction Stir Welding

The partial weak bonding phenomenon induced by an unsuitable welding parameter often occurs at the joint interface of Al/Cu dissimilar friction stir welding (FSW). Diffusion time, temperature, and pressure are the main factors that affect the diffusion behavior at the interface. Therefore, molecular dynamics (MD) simulation is used to investigate the influence mechanism of these factors from the perspectives of diffusion thickness, total energy, and volume. The diffusion time and the temperature affect the diffusion thickness significantly, whereas external pressure has little impact. The variations of total energy and volume consist of two stages, which are caused by the combined effects of lattice transformation and atomic diffusion. The variation processes of total energy and volume are accelerated with the increase in temperature due to a higher diffusion velocity, and it is delayed by external pressure at a higher temperature because the lattice transformation is inhibited. These findings are beneficial to the choice of welding parameters in actual production.

Effect of friction stir welding parameters on the material flow, mechanical properties and corrosion behavior of dissimilar AA5083-AA6061 joints

Material flow has a significant impact on the joint properties and is one of the most challenging aspects to be understood in dissimilar friction stir welding. The present study emphasizes the role of process parameters on material flow, mechanical properties and corrosion behavior of dissimilar friction stir welds of AA5083-AA6061. Microstructural analysis revealed that the onion ring sub-layer width observed at the stir zone was substantially changed by varying process parameters. It was understood that the higher rotational speeds promote better intermixing and enhanced mechanical properties. The notch tensile strength values were in correlation with the intermixing of materials at the stir zone and the highest notch tensile strength value was obtained at 1400 rpm and 60 mm/min. A remarkable degree of material intermixing and fragmentation of intermetallics at higher rotational speeds resulted in better corrosion resistance.

Effect of Tool Profile Influence in Dissimilar Friction Stir Welding of Aluminium Alloys (AA5083 and AA7068)

Friction stir welding is an innovative welding process for similar and dissimilar joining of the materials effectively. FSW simply modified the grain structure and also improved the strength of the joints for any type of alloying elements. This experimental study planned to carry out the joining process for dissimilar materials such as aluminium alloys 5083 and 7068. Three different types of tools are involved to find the ultimate tensile strength and Vickers hardness. The tool types are straight cylindrical tool, taper cylindrical tool, and triangular tool. The process factors for this investigation are a rotational speed of 800, 1000, 1200, and 1400 rpm, welding speed of 30, 40, 50, and 60 mm/min, axial force of 3, 4, 5, and 6 kN, and plate thickness of 5, 6, 7, and 8 mm. The hardness value and the ultimate tensile strength were increased in the welding zone, which proves the effects of tool profiles are efficiently utilized.

Parameters Optimization of Dissimilar Friction Stir Welding for AA7079 and AA8050 through RSM

Aluminium alloy is widely used in engineering application, and it can be classified based on the constituent elements or alloying elements. Aluminium alloy is preferred for the nature of its tensile strength, ductility, and corrosion resistance in this research to make a dissimilar friction stir welding joint of aluminium alloys 7079 and 8050 materials. The tensile strength of the weld joint is estimated by the influence of the response surface methodology approach. The welding is carried out by preferred process parameters with a tool speed of 1000–2500 rpm, tool pin diameter of 2–6 mm, welding speed of 50–300 mm/min, and tool shoulder diameter of 10–20 mm. The ANOVA analysis and the prediction of tensile strength were conducted efficiently. From the RSM analysis, the tool pin diameter mostly modified the output of the result.

Enhancing corrosion resistance and mechanical properties of dissimilar friction stir welded 5083-6061 aluminium alloys using external cooling environment

Dissimilar friction stir welding of AA5083-AA6061 alloys in different cooling environments (air, liquid nitrogen, and water) was successfully employed as an alternative method to enhance corrosion resistance and mechanical properties. The evolution of microstructure, corrosion behavior, and mechanical properties of friction stir welded joints were studied using optical microscopy (OM), electron backscattered diffraction, scanning electron microscope, electrochemical workstation, and universal testing machine. The results indicated that the width of the stir zone and grain size of heat-affected zones were reduced by the use of external cooling media. Electron backscattered diffraction results showed that the grain size in air-cooled friction stir welding, nitrogen-cooled friction stir welding and water-cooled friction stir welding were 7.6 µm, 4.5 µm, and 3.2 µm, respectively, and water-cooled friction stir welding joint developed a larger fraction of high-angle grain boundaries at stir zone. The intermetallics formed in the joints using cooling media were finer compared to that of the air-cooled samples. The corrosion behavior of the stir zone was impacted by the cooling environment while potentiodynamic polarization results revealed that the water-cooled friction stir welding joint showed excellent corrosion resistance due to the finer size of intermetallics. The minimum hardness values shifted to the stir zone in the case of nitrogen-cooled friction stir welding and water-cooled friction stir welding from the heat-affected zone location as in the air-cooled friction stir welding joint. For the joint made with water-cooled friction stir welding, maximum yield strength was obtained with a joint efficiency of 96% relative to AA5083 base material.

The Effect of Tool Rotation Speed on Hardness, Tensile Strength, and Microstructure of Dissimilar Friction Stir Welding of Dissimilar AA5083 and AA6061-T6 Alloys

The welding between two different grades of aluminum alloy, specifically AA5083 and AA6061-T6, is very difficult to obtain optimal results when using conventional welding methods such as TIG/MIG welding. Therefore, a solid-state joining technique is highly recommended to overcome these problems, one of which is friction stir welding (FSW). The effect of rotation speed on microstructure, microhardness, and tensile properties of dissimilar Friction Stir welded AA5083 and AA6061-T6 aluminum alloys were investigated. Three different rotation speeds (910, 1500, and 2280 rpm) were used to weld the dissimilar alloys. The metallographic analysis of joints showed the presence of various zones such as BM (base material), HAZ (heat affected zone), TMAZ (thermo-mechanically affected zone), and NZ (nugget zone) were observed and analyzed by mean of optical and scanning electron microscope. The results showed that increasing the rotation speed from 900 to 2280 rpm made grain coarsening in NZ and the mass distribution of the material is more evenly distributed, as well as increased hardness and tensile strength of the joint. The highest values in microhardness in NZ and tensile strength at the join were founded at the speed of 2280 rpm and 1500 rpm which was similar to 2280 rpm, respectively.

Enhancement of the Al/Mg Dissimilar Friction Stir Welding Joint Strength with the Assistance of Ultrasonic Vibration

The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.

Determination of local constitutive properties in similar and dissimilar friction stir welded joints from DIC based surface strain measurement in two mutually perpendicular surfaces

In the present work, local constitutive properties of similar and dissimilar friction stir weld (FSW) joints of AA6061-T6 and AA7075-T6 are evaluated using a modified non-uniform stress method (nUSM). The modified nUSM considers the instantaneous cross-sectional area at any section of a macro tensile (MaT) specimen as a two-variable function. These two variables are the strain in width and thickness direction during uniaxial tensile test. The strain in width and thickness direction is measured using two cameras of a stereo digital image correlation (DIC) testing instrument. These two cameras work as two separate 2-dimensional DIC placed perpendicular to width and thickness direction. However, strain data from this two 2D-DIC are arranged in a global euclidian space while maintaining a fixed pixel/mm ratio. The local constitutive properties evaluated from nUSM are then compared with the local properties extracted from longitudinal miniature tensile (MiT) specimens. The local constitutive properties evaluated using modified nUSM for the similar AA6061-AA6061 FSW joint have shown a good agreement with the properties calculated from the MiT specimen. In a similar AA7075-AA7075 FSW joint, the accuracy of the modified nUSM is affected by the relatively less deformation present in some portion of the FSW joints. The nUSM did not evaluate local constitutive properties in the AA7075 side of a dissimilar AA6061-AA7075 FSW joint, as this portion remains elastic during the uniaxial tensile testing of the MaT specimen.

Analysis of Variance of Dissimilar Cu-Al Alloy Friction Stir Welded Joints with Different Offset Conditions

In this investigation, dissimilar material AA6061-T6 and Cu B370 were joined by friction stir welding (FSW). This paper presents a feasibility study of FSW to join Al-alloy and Cu-alloy. The experiment was conducted using general full factorial design by varying the tool rotation speed, weld speed, and probe offset, and by keeping the plunge depth constant. In this research work, a statistical model was established to build a connection between the process variables and outcomes—yield strength (YS), ultimate tensile strength (UTS) and % elongation (% E). Statistical tools such as analysis of variance and scatter diagrams were employed to evaluate the suitability of the models. In addition, the impacts of the process variables on the tensile properties were investigated. From the experimental results, it can be concluded that (i) an excellent weld joint could be obtained by keeping the softer Al plate at the retreating side with a probe offset of 2.0 mm towards the softer material, and (ii) maximum tensile properties were obtained at a higher tool-rotation speed, weld speed, and with a probe offset of 2.0 mm. Further, the fractured tensile specimens were investigated using a scanning electron microscope (SEM). From the analyses, it was noted that, during the tensile test, the weld joint failed with a brittle–ductile mixed fracture mode.

Effects of SiC nanoparticles on the dissimilar friction stir weldability of low-density polyethylene (LDPE) and AA7075 aluminum alloy

Abstract Linear dissimilar friction stir welding (FSW) of metals and polymers displayed some attractive applications for crucial lightweight industries such as automotive. The substantial dissimilarity between these, unlike materials in terms of physical and mechanical properties, can affect the feasibility of this solid-state joining in an exceptionally challenging manner. In this article, an interesting approach is proposed to reduce such a tricky significant difference by strengthening the polymer during FSW treatment as the dissimilar weldment's weakest counterpart. A very soft polymer as low-density polyethylene (LDPE) and a relatively hard aluminum alloy as AA7075 were assessed under investigation for shifting the situation in terms of complexity toward the most critical state. Then, by pre-placing SiC nanoparticles inside the polymer side and afterward, they were introduced into the weld nugget during dissimilar materials mixing. The FSW processing parameters were optimized to reach a sound state of nanocomposite weld formation with superior mechanical performance. The cross-sectional investigation results announced the impact of SiC nanoparticles dispersion through the polymer matrix on dissimilar weldments' subsequent mechanical performance. The distribution of these reinforcing agents and their influence were considerably varied depending on the FSW processing parameters.