Friction Stir Welding Of AA6061-T6 Research Articles

Effect of welding speed on microstructure, nano-mechanical and nano-tribological characteristics of dissimilar friction stir welded AA6061-T6 and AZ31 alloy

The microstructural, tribological, and mechanical performance of friction-stir welded AA6061-T6 and AZ31 alloys were investigated using electron back scattered diffraction, scanning electron microscope, X-ray diffraction, and electron dispersed spectroscopy methods. The non-destructive X-ray microcomputed tomography test was used to analyse weld porosity. The distribution of volumetric and surface flaws (pores) was found to be confined across the weldment. Using a novel atomic force microscopy method, the nano-tribological characteristics of the base metal and localized regions of welded sample were studied for the first time. The significant difference in wear and friction behaviour was observed in all weld zones and base metal of magnesium side, which was correlated with the hardness of these regions. AFM results showed strong variation in tribological properties in correlation with the hardness trends of different weld zones, i.e. higher hardness leads to low wear. In weldments, intermetallic compounds such as Al12Mg17 and Al3Mg2 were produced, resulting in nanohardness differences as measured by the nanoindentation test. The joint efficiency of 65%, 84%, and 91% were obtained at welding speeds of 16 mm/min, 20 mm/min, and 25 mm/min, respectively.

EFFECTS OF SHOT PENNING ON MECHANICAL PROPERTIES, MICROSTRUCTURAL EVOLUTION AND RESIDUAL STRESS OF SUBMERGED FRICTION STIR-WELDED AA6061-T6 ALLOY

The purpose of this work is to study the effect of shot peening on the mechanical characteristics of welded plates which were performed by Submerged Friction Stir Welding (SFSW) on AA6061-T6 alloy. SFSW was carried out under three cooling mediums like water, brine solution, and coolant oil at the rotational speed of 1200[Formula: see text]rpm and welding speed of 45[Formula: see text]mm/min, respectively. The welded samples from each cooling medium were subjected to a shot peening process. A tensile test was carried out on weld peened and welds unpeened joints. The hardness of the various zones of HAZ, TMAZ, and NZ was also investigated. Optical and scanning electron microscopy was used to examine the microstructures of peened and unpeened joints formed by coolant samples. Shot peening has the potential to enhance the compressive residual stress of friction stir welded joints. According to these findings, shot peening had a greater impact on the mechanical properties of welded samples than unpeened samples, including tensile strength, percentage of elongation, and hardness. The grain size was a little bit smaller than the FSW sample because the surface of the welded samples was subjected to more strain during shot peening.

Modeling and analysis of effect of tool geometry on temperature distribution and material flow in friction stir welding of AA6061-T6

Modeling and analysis of effect of tool geometry on temperature distribution and material flow in friction stir welding of AA6061-T6

Investigation of the Effects of Tool Positioning Factors on Peak Temperature in Dissimilar Friction Stir Welding of AA6061-T6 and AA7075-T6 Aluminum Alloys.

Among the emerging new welding techniques, friction stir welding (FSW) is used frequently for welding high-strength aluminum alloys that are difficult to weld by conventional fusion-welding techniques. This paper investigated the effects of tool-positioning factors on the maximum temperature generated in the dissimilar FSW joint of AA6061-T6 and AA7075-T6 aluminum alloys. Three factors of plunge depth, tool offset, and tilt angle were used as the input parameters. Numerical simulation of the FSW process was performed in ABAQUS software using the coupled Eulerian–Lagrangian (CEL) approach. Central composite design (CCD) based on response surface methodology (RSM) was used to analyze and design the experiments. Comparison of the numerical and experimental results showed that numerical simulations were in good agreement with the experimental ones. Based on the statistical model results, plunge depth, tilt angle, and tool offset were the most significant factors on maximum process temperature, respectively. It was found that increasing the plunge depth caused a sharp increase in the maximum process temperature due to increased contact surfaces and the frictional interaction between the tool and workpiece.

Effect of Square Pin Tool on Friction Stir Welded AA 6061-T6 from the Perspective of Revolution Pitch

Effect of Square Pin Tool on Friction Stir Welded AA 6061-T6 from the Perspective of Revolution Pitch

Influence of Friction Stir Welding Parameters on Joint Defects, Temperature and Hardness of AA6061-T6 and S27JR Mild Steel FSW Joint

The influence of welding parameters such as tool plunge depth, tool travel speed and tool tilt angle on welding temperature during friction stir welding of AA6061-T6 and S275JR mild steel was the focus of this research. Thermocouple placed in the aluminum alloy plate prior to welding was used to measure the temperature during the welding of joints under different set of parameter values. Joint appearance as well as defects occurring on the surface or within the joint was observed. Microhardness profiles were also taken by measuring microhardness values across the cross section of joints. Excessive flash, tunnel defects and insufficient welding were the type of weld defects observed on different joints with different parameters. Defects were attributed to the varied parameter values affecting the heat generation as well as the flow of the plasticized material. Highest temperature was recorded by the joint fabricated using the largest tool plunge depth, owing to the increased downwards pressure. Microhardness profiles were seen to be similar for all the welded joints. A “plateau” of low microhardness value was observed for all joints associated with the thermomechanically affected zone (TMAZ) and heat affected zone (HAZ). A wider plateau was observed for joints welded with higher tool plunge depth due to higher temperature.

Mechanism of microstructure evolution and grain growth in friction stir welding of AA6061-T6 and AISI304 in air and water media

Grain size has a significant effect on the tensile strength and ductility of the friction stir welded (FSWed) joints. The size and morphology of grains, developed during friction stir welding (FSW) process, depends on amount of frictional heat generated and rate of deformation involved. In addition, grain size also depends on rate of cooling of the weld region. In the present work, evolution of microstructure in FSW of AA6061-T6 and AISI304 has been investigated by conducting FSW experiments in two different media i.e. air and water. In order to get a detailed insight of the microstructure evolution, stop-action technique was used where the experiments were interrupted by stopping the machine, followed by water quenching of the samples. Detailed study about the microstructure evolution, in different weld regions, has been performed by using Electron Back Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM) techniques. The microstructures were characterized by analyzing the recrystallized grains, and grain growth. Particle stimulated nucleation and strain induced boundary migration were observed to be the recrystallization mechanisms. FSW in the water medium yields finer microstructure in the weld regions than air medium. Grain growth was observed after coalescences of sub-grains. Results have shown higher grain growth for FSW in air medium. Results have also shown transformations of Goss {110}<100> and B{110}<112> textured grains of base aluminum into Copper {112}<111>, E{111}<110> and F{111}<112> dominated textured grains at the stir zone (SZ). Water medium produced relatively highly shear textured grains than air medium at SZ.

Applicability of unique scarf joint configuration in friction stir welding of AA6061-T6: Analysis of torque, force, microstructure and mechanical properties

The present research introduces a unique concept of scarf joint technique in friction stir welding (FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality. A new joint configuration with two distinct scarf angles (75° and 60°) was considered in this study. The various aspects of welding were compared with contemporary simple square butt (SSB) joint configuration. Welding was carried out at a constant tool rotation speed (TRS), tool traverse speed (TTS) and tool tilt angle of 1100 rpm, 2 mm/s and 2°, respectively. The results are analyzed in terms of force and torque distribution, microstructure, macrostructure, and mechanical property perspective for different joint configurations. The study reveals the minimum amount of force and torque at 60° scarf angle joint configuration compared to that of square butt joint configuration. Macro study shows that all the joints were defect-free, and a prominent onion ring was present in the lower portion of the weld nugget (WN). Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration (SJC). The maximum ultimate tensile strength (UTS) and maximum average NZ hardness of 267 MPa and 83.82 HV0.1 were obtained in SJC3 at a scarf angle of 60°. It has been observed from the investigation that the joint efficiency increases from 72.5% (SSB) to 86% (SJC3) at a 60° scarf angle. This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.

Coupled Eulerian–Lagrangian prediction of thermal and residual stress environments in dissimilar friction stir welding of aluminum alloys

The evaluation of residual stresses (RS) induced by the friction stir welding (FSW) process is crucial in anticipating the performance of the welded structure. The existence of such residual stresses within a friction stir welded structure may lead to excessive distortion and weakness to afford the applied external loads. To assess quantitatively the effect of these residual stresses generated by FSW process, the current paper implements a Coupled Eulerian–Lagrangian (CEL) finite element simulation to analyze both thermal and subsequent resulted remaining stress environments in dissimilar friction stir welding of AA6061-T6 and AA2024-T3 alloys. The thermal analysis step was conducted first and followed by a mechanical analysis step in which the residual stresses distribution throughout the whole dissimilar FSWed alloys were captured. To validate the simulation results, K-type thermocouples, in addition to A-type rosette strain gauges, were planted to measure both temperature history and residual stress field generated as a consequence of the thermal environment. The effect of changing FSW working variables like rotation and traverse speeds on both the thermal and residual stress environments was investigated. The obtained results demonstrated that the temperature, as well as the residual stress, was higher in the sample retreating side rather than the proposed advancing side, and a fair correlation between the experimental and simulation results was attained. Quantitatively, the longitudinal residual stress was higher in contrast to the transverse value, and it varied from being tensile in the zone beneath the tool shoulder to compressive away from the welding tool. Furthermore, the plastic strain produced owing to the surface contact between the welding tool and the dissimilar aluminum sample was higher on the retreating side.

Effects of Brass Interlayer on Mechanical Properties of Friction Stir Welded AA 6061-T6 Joint

The most important issues in the joining of similar aluminum alloy are softening of weld zone and reduction in tensile strength of joints. Use of a metallic interlayer can resolve these issues. In the present research work, effect of brass interlayer on the properties of friction stir welded 6061-T6 aluminum alloy was studied. X-ray diffraction analysis was carried out to investigate the phase composition with brass interlayer. Al2Cu and Al4Cu9 intermetallic compounds were formed at the welded zone. Mechanical properties were examined through the tensile and microhardness testing. Tensile test results reveal that the use of brass interlayer is a good solution to improve the joint strength, as the insertion of brass interlayer enhances the joint strength up to 36%. In addition, use of brass interlayer enhances the microhardness at the weld zone and the softening issue has been resolved to some extent. Field emission scanning electron microscopy was used to investigate the mechanism of fracture behavior in fractured tensile specimens. However, insertion of brass interlayer slightly changes the ductile fracture toward brittle fracture.

Effects of bottom plate in friction stir welding of AA6061-T6

The effects of 40 mm width bottom plates on the microstructural modifications and the mechanical properties of a 6 mm thick FSW AA6061-T6 joint have been investigated. The bottom plates are placed partially at the weld zone to absorb and dissipate heat during the welding process. An axial load of 5 to 7 kN, a rotational speed of 500 rpm, and a welding speed of 50 mm/min are employed as welding parameters. The size of the nugget zone (NZ) and heat-affected zone (HAZ) in the weld joints obtained from AISI 1040 steel bottom plate is more significant than that of weld joints obtained using copper bottom plate due to lower thermal conductivity of steel. Also, the weld joints obtained using copper bottom plate have fine grain microstructure due to the dynamic recrystallization. The friction stir welded joints obtained with copper bottom plate have exhibited higher ductility of 8.9% and higher tensile strength of 172 MPa as compared to the joints obtained using a steel bottom plate.

Role of Mg2Si particles on mechanical, wear, and corrosion behaviors of friction stir welding of AA6061-T6 and Al-Mg2Si composite

This paper investigates the effect of different tool pin morphologies on the inter-mixing capability, microstructure, mechanical properties, corrosion, fracture, and wear behaviors of the dissimilar friction stir welded AA6061-T6 alloy--Al 20wt% Mg2Si composite. Grooved shoulder tools with varying pin profiles such as tapered cylindrical, threaded tapered cylindrical, and triangular tapered pins were used for joining the base materials. The parameter combination of 80 mm/min travel speed and 1000 r/min rotation speed (at which no visible flow-induced defect was obtained) was used for this study. Among the pin profiles, the triangular tapered pin produced significantly improved intermingling/inter-material flow, fragmentation, and dispersion of the primary Mg2Si particles in the AA6061-T6/Al-Mg2Si joint. The triangular tapered tool reduced the average grain sizes of the AA6061 alloy and the Mg2Si particles from 18.4 to 4.6 µm and from 115 to 7.5 µm, respectively. Intermetallic phases of Mg2Si, AlFe, Al3.21Si0.47, and Al0.7Fe3Si0.3 are formed in the weld nugget of all the AA6061/Al-Mg2Si joints. The tensile strengths of the joints fabricated with tapered cylindrical, threaded tapered cylindrical, and triangular tapered tools are 108, 139, and 141 MPa, respectively. Abrasive wear is promoted in the joints fabricated with triangular tapered tool due to the homogeneous dispersion and fragmentation of the inherent hard Mg2Si particles. The corrosion attack is dependent on the fragmentation level of the Mg2Si phase. Triangular tapered pin tool is recommended for dissimilar Al/composite welding due to favorable tool-induced material flow, dispersion, and fragmentation of reinforcement.

Welding condition & microstructure of friction stir welded AA 6061-T6 and AZ31B

Dissimilar friction stir welding between 6061-T6 Al alloys to AZ31B Mg alloys with a plate thickness of 6 mm was investigated. Defect-free welds were obtained at a different rotational speed ranging from 400 to 700 rpm with welding speed of 0.5–0.8 mm/sec, respectively. The influence of welding speed and rotational speed was investigated to reveal the microstructure growth and microhardness of weld joint that displays tortuous interface as well as intermetallic compounds. Irregular distribution of microhardness was found due to complex microstructure. Intermetallic compound Al3Mg2 and Al12Mg17 were revealed by energy dispersive spectroscope (EDS) analysis. Compared to the base metal value of maximum microhardness was double in the stir zone.

Response Optimization of process parameters of friction stir welded AA6061 T6 and AA 7075 T651 Using Response Surface Methodology

In this work friction stir welding of AAA 6061 T6 with 7075-T651 of 6mm thickness was carried out. A 31 run Central composite design was adopted to run the experiments. The process parameter ranges were identified based on trial runs. The optimization of the process parameters was done based on the results and plots obtained from Design Expert 10.0 software and the mathematical model was developed for the same. The microhardness tests were also studied. The advancing side was 6061 T6 due to its formability properties. Interference of each process parameters on the Tensile strength was obtained from the contour plots. The fitness was justified by Anova.

Investigation of tensile strength on friction stir welded joints of dissimilar aluminum alloys

Abstract The main aim of this paper is to study the feasibility of friction stir welding of AA6061-T6 & AA6082 and to examine the effect of process parameters like geometry of the tool pin, rotational speed of the pin, welding speed and tilt angle on tensile strength of welded joints. Experimental results based on Taguchi method confirm that tool rotational speed has major contribution to tensile strength as compared to speed and tilt angle in case of both circular and square pins. The welded joints produced by circular pin show superior strength of the joint than that of the square pin.

Friction-stir welding of AA6061-T6: The effects of Al2O3 nano-particles addition

In the present work, attempts were made to fabricate Al-based nanocomposites by Friction Stir Welding (FSW) process. Al2O3 nanoparticles were added into the aluminum matrix for refining the microstructure of the nugget zone (NZ) and to restrict the growth of granularly in the heat-affected zone (HAZ). The effects of Al2O3 nanoparticles addition on the grains structure evolution and various mechanical behavior of friction stir welded aluminum matrix was studied and elaborated in detail. The findings revealed that the addition of Al2O3 nanoparticles resulted in remarkable refining of grains in the nugget zone due to pinning effect produced by nano-sized Al2O3 particles which prevent the grain growth followed by recrystallization during FSW, leading to a remarkable reduction in grain size. A significant increment in tensile strength, micro-hardness and wear properties compared to sample without nanoparticles under the same operating conditions is attributed to nano-sized Al2O3 particles addition in the nugget zone. Also, the samples joined with rotating and transverse velocities of 2000 rpm and 70/80 mm/min showed higher tensile properties. However, the employment of single FSW pass resulted in an unusual Al2O3 nanoparticles distribution and void initiation at the interface between Al-matrix and Al2O3 nanoparticles in the heat-affected zone resulted in the sudden premature fracture of the specimen during tensile loading.

Unusual fatigue behavior of friction-stir welded Al–Mg–Si alloy

In this work, high-cycle fatigue behavior of friction-stir welded AA6061-T6 was studied. An emphasis has been made on the inter-relationship between microstructure, residual stress and fatigue resistance. The welds were produced under optimized conditions, including a combination of relatively high welding temperature and rapid cooling rate, and subsequently undergone a standard post-weld aging heat treatment. The optimized welds exhibited excellent fatigue performance that was comparable (or even superior) to that of the base material. This result was attributed to a considerable grain refinement in the stir zone, subtle material softening in the heat-affected zone as well as to significant residual stress generated during the optimized FSW.

Friction stir welding of aluminum 6061-T6 in presence of watercooling: Analyzing mechanical properties and residual stress distribution

Underwater friction stir welding of AA6061-T6 was carried out in order to improve mechanical properties of fabricated joints in butt mode configuration. Full factorial experimental design was used to design the required experiments and finding effect of water cooling on various combinations of tool rotation speed and travel speed. It was found that by applying water cooling condition, the tensile strength and hardness of the joints can be improved about 16% and 12.5% respectively. Also, research findings showed that the elongation is deteriorated by applying cooling condition and reaches from average values of 10.46%–6.98%. From microstructure analysis, it was found that grain refining and prevention of heat affected zone from softening are main mechanisms for improving the welding strength and hardness. Also, residual stress distribution showed that applying watercooling to FSW process causes increase of magnitude and depth of compressive residual stress that significantly reduces the deflection of the sample after unclamping.

Effect of Threaded Pin Tool for Friction Stir Welding of AA6061-T6 at Varying Traverse Speeds: Torque and Force Analysis

Friction stir welding (FSW) of 6-mm-thick AA 6061-T6 plates for taper threaded tool were studied in this investigation in terms of torque and different forces. A plain taper tool in addition to threaded tool is also incorporated in the study to analyze the effectiveness of threads. Welding was conducted at a constant rotational speed of 1100 RPM and varying traverse speeds between 45 and 135 mm/min. The distribution of torque, Z-force and X-force generated during the FSW process discloses a substantial knowledge about the weld formation. The torque and forces increase with the increase in traverse speed for both the tools where higher values were attained by taper threaded tool. The macrostructure reveals a sudden increase in thickness of shoulder induced region and nugget area, followed by a gradual decrease for both of the tools with traverse speed. Comparatively larger shoulder induced region and weld nugget are obtained for taper threaded tool. The maximum values of these entities were attained at 75 mm/min for taper threaded tool, and a difference of 0.13 mm and 7.52 mm2, respectively, was obtained with taper tool. Finer grains with an average diameter of 5.82 µm are obtained for taper threaded tool and 8.68 µm for taper tool. Maximum tensile strength was obtained for taper threaded tool with a joint efficiency of 70.96% and 60.32% for taper tool. A mixed mode of failure is observed at a higher traverse speed for taper tool, whereas all welds for taper threaded tool exhibit ductile fracture.

Dissimilar Friction Stir Butt Welding of AA6061-T6 and AA6061/SiCp Composite: Microstructural Characteristics, Impact Toughness, Hardness, Strength Under Transverse Impact

Impact response of dissimilar friction stir welded (FSWed) joints between a monolithic alloy and metal matrix composite has not been yet reported and thus requires a detailed investigation. Therefore, an exhaustive research on the microstructure, microhardness, tensile properties, fracture toughness and failure response under transverse impact of the FSWed AA6061-T6/AA6061 + SiCp joint was conducted within the study. The plates of size 300 × 120 × 3.2 mm3 were friction stir butt welded using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min, tilt angle of 1° and a penetration depth of 0.2 mm into the upper surface of the workpieces. The obtained results indicated that there is no defect in the weld zone of the FSWed dissimilar joint. Microhardness distribution across the mid-thickness of the joint demonstrated superior Vickers hardness within the nugget zone compared to that of AA6061-T6. In addition, tensile rupture took place away from the weld region on the advancing side in the joint for all transverse tensile test specimens. It was also demonstrated that the FSW process resulted in a significant enhancement in fracture toughness compared to those of the base materials. Furthermore, weld nugget of the joint withstood the applied transverse impact energies ranging between 2.5 and 7.5 J.