Grains In Stir Zone Research Articles

Electrochemical behavior and microstructural characterization of nano-SiC particles reinforced aluminum matrix composites prepared via friction stir processing

The present work aims to elucidate the mechanism of microstructural evolution in different regions of nano-SiC particles reinforced aluminum matrix composites prepared by friction stir processing (FSP) on its electrochemical behavior. Electron backscatter diffraction technique (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution of stir zone (SZ), advancing side thermomechanically affected zone (AS-TMAZ), retreating side thermomechanically affected zone (RS-TMAZ) and base metal (BM). The electrochemical behaviors of the above zones were investigated using electrochemical tests. A homogeneous and fine microstructure is formed in SZ, not only the nano-SiC is homogeneously distributed within the grains with an average grain size of 3.5 μm, but also the recrystallized grains account for the highest percentage of 85 %. The potentiodynamic polarization curve indicates that the corrosion current densities of the BM, RS-TMAZ, AS-TMAZ and SZ are 0.89, 0.39, 0.85 and 0.36 μA/cm2, respectively, while the polarization impedances are 33.40, 51.42, 48.72 and 73.79 kΩ cm2, respectively. Combining the Nyquist and Bode plots analysis, the optimal electrochemical corrosion resistance is in SZ. The fine and homogeneous recrystallized grains in SZ significantly improve its electrochemical corrosion resistance. This is mainly ascribed to the increase in crystal defects as a result of the increase in grain boundaries, elevating the electron scattering. Simultaneously, the increase in high-energy state grain boundaries is beneficial to the rapid formation of a thicker passivation film.

Microstructural characterization and corrosion-resistance behavior of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy joints

This study examined the effect of traverse speed on the mechanical properties, corrosion-resistance behavior, and microstructure of friction stir-welded A390/10 wt% SiC composites-AA2024 Al alloy joints. The laminar flow of both materials was found to diminish in the stir zone (SZ) when the traverse speed of the tool increased from 40 to 80 mm/min, lowering their mixing rate. Large aspect ratio Si particles are broken by the tool pin-induced applied plastic strain, which turns them into refined equiaxed particles. Their aspect ratio remains unchanged in the SZ, despite their decreasing size. SiC and Si particles progressively come into view when moving from the AA2024 alloy's SZ to the composite workpieces. These changes happen abruptly as traverse speed increases due to the lack of an interfacial layer structure. The advancing side (AS)'s SZ grain size drops from 4.2 ± 0.3 μm to 1.2 ± 0.2 μm as the traverse speed drops from 80 to 40 mm/min. Increased traverse speed from 40 to 80 mm/min will result in a 5.8% decrease in elongation percentage (EP) and 8.4%, 36%, and 10.3% increases in the ultimate tensile strength (UTS), corrosion resistance, and yield strength, respectively.

Modeling of stir zone grain size variation in the friction stir processed Al-2024 according to the FSP parameters

Modeling of stir zone grain size variation in the friction stir processed Al-2024 according to the FSP parameters

Microstructure, tensile properties and fracture toughness of friction stir welded AA7075-T651 aluminium alloy joints

Abstract The main objective of this investigation is to study the microstructure, tensile properties and fracture toughness of friction stir welded (FSW) butt joints of 10 mm thick AA7075-T651 plates. The microstructural features of stir zone (SZ), thermos-mechanically affected zone (TMAZ), heat affected zone (HAZ) were analyzed using optical microscopy technique. The tensile properties were evaluated using smooth and notch tensile specimens and compared to base metal properties. The microhardness survey was done across the weld cross section and correlated to the failure of tensile specimens. Compact tension (CT) specimens were used to evaluate the fracture toughness of welded joints. The fractured tensile and CT specimens were analyzed using scanning electron microscopy (SEM). Results showed that the FSW AA7075-T651 specimens welded using axial load of 12 kN, tool rotation speed of 750 rpm and welding speed of 30 mm/min exhibited 412 MPa tensile strength and 9% elongation. It showed 88 and 89% of base metal strength elongation. The joints showed fracture toughness of 23 MPa m1/2 which is 80% of base metal fracture toughness. The superior tensile and fracture toughness properties of joints are mainly attributed to the evolution of finer grains in SZ due to the stirring action of FSW tool.

Strain rate and microtexture analysis of rapid-quenched AA6061 friction stir welds produced with tool eccentricity

The paper investigates the effect of tool eccentricity on the strain rate and microtextures produced in rapid-quenched AA6061 friction stir welds. Thermocouples are embedded in the tool and the thermal cycle are recorded via a data acquisition system. Stir zone grain refinement is observed in all samples, with the eccentric sample having the finest grains (3.18 μm). The strain rate is measured to be between 0.17 and 51.94 s−1, with the eccentric sample experiencing the highest strain rate. The pole figures indicate crystallographic textures shifted approximately 90° when tool eccentricity is employed. The aligned samples have a strong {11-2}<1-10> B simple shear texture component, while the eccentric sample shows morphological changes towards a strong {11-1}<1-10> A simple shear texture component.

Microstructural and Mechanical Characteristics of Pure-Cu/brass Dissimilar Joints Welded by Friction Stir Welding Using Various Process Parameters

FSW (friction stir welding) is a solid-state joining method that attracts interest from all industries. The influence of various tool rotational speeds on the microstructure and mechanical characteristics of dissimilar pure Cu-brass joints has been investigated. The travel speed and vertical load were kept constant in the welding trials, at 40 mm/min and 10 kN, respectively, while the tool rotational speed varied from 1000 to 1400 rpm. The increase of the rotational speed to 1400 rpm resulted in degradation of the mechanical properties. The stir zone grain structure was refined; however, the grain size was irregular. Grain refining occurs due to a continuous and discontinuous dynamic recrystallization mechanism. In the grain interior, there were many large dislocations, identifying that incomplete recrystallization took part within the SZ. Instead, the lower rotational speed, i.e., 1000 rpm, led to more uniform grain refinement in the SZ. Moreover, in contrast to the welded zone where very fine grains exist, the base metal and thermomechanically heat-affected zone display coarser grains. Because of the microstructural modification, the stir zone’s mechanical characteristics were higher than the base materials, and the mechanical strength and plasticity were simultaneously upgraded. These results indicate that the size of the grains is independent of rotational speed. And mechanical properties like hardness and impact strength decreased as the rotational speed increased.

Influence of brass interlayer and water cooling on microstructure, mechanical and corrosion behaviour of friction stir welded AA6061-T6 alloy

This study investigated the effect of brass interlayer and water cooling on the mechanical properties and corrosion behaviour of friction stir welded AA6061 alloy. Although grain refinement was observed in the stir zone (SZ) of FSW without interlayer, strength loss occurred due to thermal softening. The insertion of a brass interlayer resulted in more grain refinement which could be attributed to brass particles acting as a nucleation site for further recrystallization. The weld strength with interlayer improved due to the formation of strengthening intermetallic compounds (IMCs) such as Al2Cu and Al4Cu9. However, the strength recovery is not attainable in a heat-affected zone (HAZ). Moreover, hard and brittle IMCs formed in SZ of weld with interlayer resulted in premature failure. Therefore, water cooling was used to enhance the hardness in HAZ. Very fine grains in SZ with a high fraction of high angle grain boundaries were obtained with water cooling FSW with interlayer, while HAZ softening was also reduced. Moreover, the water-cooling FSW with interlayer inhibited the formation of brittle intermetallics and decreased volume fraction of IMCs attributed to faster cooling rate. Thereby the strength of the overall weld joint was enhanced. The corrosion test was performed in 3.5% NaCl solution. The corrosion findings stated that the decrease in the number of intermetallics formed low galvanic coupling with aluminium matrix resulted in better corrosion resistance and minimum corrosion rate for water-cooled FSW than natural cooling.

A specific analytical study of friction stir welded Ti-6Al-4V grade 5 alloy: Stir zone microstructure and mechanical properties

The light metal titanium alloys find extensive usage is in industries where weight is a significant factor. Research in friction stir welding (FSW) aimed at producing strong joints without adding extra weight since machines like aircraft and automobiles must have as little weight as possible to improve their fly-to-buy ratio. This study reports 10 mm thick titanium alloy plates that are FSWed by varying rotational speed and tool traverse speed using the W-La2O3 tool. Due to the heat produced during the welding process, each material region experiences a different thermal cycle, which significantly affects microstructural changes. The peak temperature during FSW exceeded the β-transition temperature, causing phase transformations in the stir zone (SZ). A lamellar structure was observed in the SZ, and a transition line region (TLR), Bimodal, or duplex microstructure obtained consists of (α + β) phase. The SZ grain size decreases along the thickness direction, tensile strength increases, and reaches 89–102% of the base material. A lower hardness value is found in the SZ than in the base material (BM). The tensile fracture surface is observed to have a honeycomb-like structure or dimples, representing ductile fracture.

Evaluation of microstructure and tribological behavior of FS-processed Al/SiC-BNh hybrid composite on the Al-1050 substrate

In this research, in order to improve the wearing property Al-1050 the Al/(SiC+BNh) hybrid composite was synthesized via friction stir processing (FSP) on the Al-1050 substrate and its tribological behavior was compared with FS-processed Al/SiC and Al/BNh mono surface composite layers. Microstructural studied revealed dynamic recrystallization caused significant grain refinement in the stir zone (SZ) i.e., considerable reduction of SZ grain size in comparison to base metal. Increasing of FSP pass numbers from 3 to 5 passes resulted in increasing of SZ hardness and reduction of SZ grain size from 11 ± 2 µm to 6 ± 1 µm. Wearing tests indicated that hybrid Al/(SiC+BNh) composite has a higher wear resistance than Al/SiC and Al/BNh layers. The reduction of wear rate was in the following order: base metal (0.075 mg/m), FS-processed Al/SiC (0.047 mg/m), FS-processed Al/BNh (0.046 mg/m) and FS-processed Al/SiC+BNh (0.039 mg/m).

Microstructural evolution and mechanical properties of friction stir welded 12Cr-ODS steel

Abstract 12Cr oxide dispersion strengthened (ODS) steel was welded by friction stir welding (FSW) method. The weld joint is composed of heat-affected zone (HAZ), advancing side thermo-mechanically affected zone (AS-TMAZ), retreating side thermo-mechanically affected zone (RS-TMAZ) and stir zone (SZ). Electron back scattering diffraction (EBSD) results reveal that dynamic recrystallization occurs in SZ and AS-TMAZ, and the size and orientation of the grains change drastically compared with base mental (BM). Structures transfer from elongated grains in BM towards equiaxed grains in SZ. The dynamic recrystallization process is accompanied by a transition from low angle boundaries (LAB) to high angle boundaries (HAB). In SZ, parts of oxide particles are found to agglomerate together. High compressive stress exists in all the FSW joint region, and two peaks are detected in AS-TMAZ and RS-TMAZ, respectively. Compared with the hardness of BM (295 HV), the hardness of SZ increases obviously, and the highest value is up to 350 HV.

New method to enhance the mechanical characteristics of Al-5052 alloy weldment produced by tungsten inert gas

Tungsten inert gas welding method is widely used to weld aluminum alloys. However, the development of some defects such as porosity and undercutting which form during tungsten inert gas welding may decrease the quality of the weld. Processing of the joint by friction stir processing is a method to enhance weld quality. In the current work, the weld area produced by tungsten inert gas is processed by friction stir processing as well as a novel processing method entitled “friction stir vibration processing.” In friction stir vibration processing, the specimen is vibrated while friction stir processing is carried out. The results show that both processing methods lead to grain refinement in the weld region and increase the strength and ductility of the tungsten inert gas–welded specimen. The stir zone grain sizes of friction stir vibration–processed samples are less than those of friction stir–processed ones. It is believed that workpiece vibration in friction stir vibration processing increases the material straining and intensifies the dynamic recrystallization. By application of friction stir processing on tungsten inert gas–welded specimen, ultimate tensile strength and ductility increase by about 10% and 22%, respectively. They increase by about 17% and 33%, respectively, as friction stir vibration processing is applied. The results also indicate that the effect of friction stir vibration processing on the microstructure of the weld region and its mechanical properties increases as vibration frequency increases. Friction stir vibration processing is a good alternative for friction stir processing, and it is recommended for application in industry.

Strength, failure and microstructure development for friction stir welded AA6061-T6 joints with different tool pin profiles

The influence of seven different tool pin profiles was investigated to appraise the tensile, flexural strength, fracture behavior, and microstructure evolution in friction stir welded similar AA6061-T6 joints. Results indicate that each tool pin profile affects the material flow/intermixing in different ways; consequently, the weld nugget feature and grain size in the stir zone (SZ) were also observed to be different. Relatively finer grains with homogenous microstructure in SZ were observed for joints prepared using cylindrical grooved with straight flutes (CGF) and cylindrical grooved (CG) tool pins. The highest tensile strength and flexural load were observed for joints obtained with CGF tool pin followed by CG tool pin. A relationship between average yield strength of the joint and inverse square root of average SZ grain size was established for these joints. EBSD analysis revealed that the SZ is the mixture of low angle grain boundaries and high angle grain boundaries (HAGBs) and the fraction is controlled by different pin profiles. The HAGBs and high shear texture components B/B¯ and C were found predominant in welds prepared with CGF and CG tool pins. Fractographic analyses showed the presence of numerous dimples in sound bonded regions indicating the ductile fracture; however, tearing/rupture and shear failure were witnessed near the vicinity of the tunnel region.

The investigation into vibration effect on microstructure and mechanical characteristics of friction stir spot vibration welded aluminum: Simulation and experiment

In this study, an innovative technique is employed to modify the microstructure and increase the mechanical characteristics of the Al5083 joint made by friction stir spot welding (FSSW). In this technique entitled FSSVW (friction stir spot vibration welding), the workpiece is vibrated during FSSW. Noted processes were modeled and finite element simulation results were also analyzed. The results showed that workpiece vibration during FSSW led to grain refinement, larger weld region, and improvement of the mechanical properties, namely tensile shear strength and hardness, of the joint. Stir zone grain size decreased by about 25% and tensile shear strength value increased by about 20% by applying workpiece vibration during FSSW. The results also indicated that the tensile shear strength and hardness enhanced, as vibration frequency increased. It was concluded that the presence of vibration increased the material deformation in the stir zone and led to enhanced deformation of the material. This intensified the dynamic recrystallization and resulted in grain refinement. It was also found that tensile residual stresses developed in the stir zone of FSS and FSSV welded specimens and tensile residual stress values for FSSV welded specimens were higher than those for FSS welded specimens for about 10%. It was concluded that the effect of grain size on hardness is higher than the effect of residual stress. Higher ductility is predicted for FSSV welded specimen with higher vibration frequency and also for specimen welded with less dwell time; finite element simulation was also applied to analyze the effects of workpiece vibration during FSSW on strain distribution as well as hardness and residual stress distribution within the joint during FSSW and FSSVW processes. Finite element simulation results had good compatibility with experimental results. It was concluded that the strain values and flow velocity relating to the FSSVW process are higher than those relating to the FSSW process.

Development of AZ91/SiC surface composite by FSP: effect of vibration and process parameters on microstructure and mechanical characteristics

A surface composite layer enhances the mechanical characteristics of a surface while retaining the properties of the base material. Friction stir processing (FSP) is a method for forming surface metal matrix composites (SMMCs) that reinforce a surface with particles. In the current study, a new method entitled friction stir vibration processing (FSVP) was applied to form SMMCs on the surface of AZ91 magnesium alloy with SiC particles as the reinforcing particles. Contrary to FSP, in FSVP, the workpiece was vibrated normal to the processing line while the tool rotated and traversed. The microstructure and mechanical properties of friction stir (FS) and friction stir vibration (FSV) processed specimens were evaluated. Additionally, the effects of vibration frequency and process parameters on different characteristics of FS and FSV processed specimens were studied. The results showed that the stir zone grains for FSV processed specimens were finer than those for FS processed specimens, and the second phase particles (SiC particles) had a more homogenous distribution in the former specimens than in the latter specimens. This was related to the effect of workpiece vibration during FSVP, which increased the material deformation and led to enhanced dynamic recrystallization and the breakdown of agglomerated SiC particles. The results indicated that the stir zone grain size decreased, and the distribution homogeneity of the SiC particles increased as vibration frequency increased. It was also observed that the stir zone grain size increased, and the mechanical properties of the processed specimens decreased as tool rotation speed increased.

Advanced Approach to Modify Friction Stir Spot Welding Process

Nowadays, friction stir spot welding (FSSW) is used in automotive, rail vehicle construction, the aerospace industry, and electrical industry. In the current research, a modified version of the FSSW process entitled friction stir spot vibration welding was introduced to join Al5083 specimens. The joining specimens were vibrated normal to the tool movement direction, while the joint position cooled by passing coolant through the fixture. Different characteristics of developed joint namely microstructure, mechanical properties, corrosion behavior were studied. The results showed that stir zone grain size decreased significantly as the vibration was employed and the joint position was cooled. It was found that vibration enhanced the dynamic recrystallization and coolant decreased the grain growth. Both led to enhanced grain refinement in the stir zone. The results also indicated that shear strength and hardness of the weld region increased as the modified version of FSSW was applied. Corrosion tests revealed that corrosion resistance increased as the modified method was applied.

Metallurgical behavior and variation of vibro-acoustic signal during preheating assisted friction stir welding between AA6061-T6 and AA7075-T651 alloys

Abstract The present work investigated the effects of pin profiles (cylindrical and square), pin eccentricity (0.5 mm and 1 mm) in cylindrical tool and preheating (secondary heating) on metallurgical behavior, variation of vibro-acoustic signal pattern and joint strength during friction stir welding (FSW) between AA6061-T6 and AA7075-T651 alloys. The eccentric tool pins were observed to provide good flowability and intermixing between dissimilar metals, increased the size of stir zone, and the grains in stir zone were sufficiently finer with eccentric tool pin than concentric pin. The magnitude of vibro-acoustic signal increased when shoulder plunging started and drop in signal was noted when the tool shoulder reached its desired depth. The signal magnitude was noted to be higher in welding stage compared to tool plunging stage as the tool took in fresh material during tool movement along the weld path. Preheating the workpiece prior to pin plunging and during welding notably influenced the flow behavior and mixing pattern, and the grains in stir zone were slightly coarser than those in specimen without preheating. Significant reduction in the magnitude of the signal was also observed after preheating. Tensile and flexural strength of joints were also improved slightly when additional heating was employed.

Metallurgical and Mechanical Characterization of Double-Sided Friction Stir Welded Thick AA5083 Aluminum Alloy Joints

In this paper, double-sided friction stir welding was employed to join the thick AA5083 alloy plates. The effects of rotational speed, traverse speed and pin length on the join features were evaluated. For this purpose, macro- and microstructural evolutions, and mechanical properties such as microhardness, tensile strength and fracture toughness were studied. According to the results, the stirring action and generated heat led to the fragmentation of Al6(Mn, Fe) particles and dissolution of Al3Mg2 compounds in the stir zone (SZ). The SZ grain size was much smaller than that of the other zones; however, the hardness remained almost the same alongside the joint area (~ 80 HV). An increase in rotational speed at a low traverse speed caused the increase in the grain size of the SZ; however, at a high traverse speed, it did not have any important effect on the average grain size. The highest double-sided failure energy of the joints was obtained by the traverse speed of 80 mm/min, the rotational speed of 1000 rpm and the pin length of 6 mm. In order to study the resistance to crack growth, fracture toughness (three-point bending) test was done. The results show that the KQ obtained for the optimum welded sample is about 11.5% higher than that of the base metal.

Influence of Cu powder on strength, failure and metallurgical characterization of single, double pass friction stir welded AA6061-AA7075 joints

The present work investigates the effect of copper powder addition during single pass and double pass friction stir welding (FSW) between AA6061-T6 and AA7075-T651 to appraise the formation and detailed characterization of the intermetallic compounds (IMCs) in addition to study tensile, flexural strength, material flow, and fracture behavior. The copper powder was added in three different ways namely over the plate top surface (along weld path, below the tool shoulder), inside the slots of 1 mm and 2 mm (combined slot width at faying surfaces of adjoining plates) in addition to plate top surface. Analysis was also carried out employing a quick weld stop approach keeping the tool pin inside the weld seam and sectioning through it. Small improvement in joint ultimate tensile strength and flexural load was noticed when copper powder was added on plate top surface. For joints obtained with the addition of Cu powders in slots, formations of large clusters of particulates and/or IMCs were observed. Detailed characterization revealed that the formation of IMCs in small quantity with finer size distributed evenly could be beneficial for improving joint strength. However, large chunks/lumps can promote quick and brittle failure. In double pass FSW (with second pass in the reverse direction of first pass) good material flowability and slightly finer grains in stir zone (SZ) were observed. Comparatively smaller size agglomerates were also noticed distributed on either side of the SZ after the second pass. Fractographs showed the presence of numerous micro-voids and dimples in sound joints indicating the ductile fracture. However, tearing/rupture and brittle failure were witnessed in the joints prepared with addition of Cu powder in slots.

Influence of Pin Offset on Microstructure and Mechanical Properties of Friction Stir Welded Mg/Ti Dissimilar Alloys

The influences of pin offset on the formation, microstructure and mechanical properties of friction stir welded joint of Ti6Al4V and AZ31B Mg dissimilar alloys were investigated. The results show that sound joints are obtained at different offsets. With the offset decreasing from 2.5 to 2.1 mm, the number of Ti alloy fragments is increased, and the stir zone (SZ) is enlarged and the grains in SZ become coarser. A hook-like structure is formed at the Mg/Ti interface and its length is increased with the decrease in pin offset. The Al element has an enrichment trend at the Ti alloy side near the Mg/Ti interface when the offset is decreased, which is beneficial to the bonding of the interface. An Al-rich layer with a thickness of 3–5 μm forms at the offset of 2.1 mm. All the joints fracture at the interface and present a mixed ductile-and-brittle fracture mode. The joint tensile strength is increased with the offset decreasing from 2.5 to 2.1 mm, and the maximum tensile strength of 175 MPa is acquired at the offset of 2.1 mm.

Development of High-Strength and High-Electrical Conductivity Cu–Zr Alloy Through Friction Stir Processing

Friction stir processing (FSP) is a solid-state processing technique to enhance the surface properties of the metallic materials. The present study aims to improve the surface mechanical and wear properties of Cu–0.18wt.%Zr alloy through FSP without deteriorating its electrical conductivity behavior. The Cu–Zr alloy was friction stir processed at a constant tool rotation speed of 600 rpm and by varying the tool travel speed from 50 to 200 mm/min. The specimens were extracted from the stir zone to characterize its microstructure, mechanical properties and wear behavior. It was observed that the average size of grains in stir zone decreased from 40.5 to 4.6 µm with the increase in tool travel speed, whereas hardness of the processed specimens increased from initial 70 to 99 Hv. The coefficient of friction was decreased from 0.4 to 0.07 (µ) as travel speed increased. Consequently, the wear resistance of the processed samples increased with the travel speed. The change in electrical conductivity, as measured using eddy current technique, was noted to be insignificant in the processed specimens, i.e., it decreased to 77.4% IACS from its initial 78.2% IACS. Hence, the objective of improving the mechanical and wear resistance properties of Cu–Zr alloy was achieved without impairing the electrical conductivity by friction stir processing. The results suggest that friction stir processing can be effectively used to improve the wear behavior of high-strength and high-electrical conductivity alloys.