Single Pass Friction Stir Processing Research Articles

Strength-ductility synergy in a graphene oxide reinforced aluminum matrix composite made by friction stir processing

The present study examines the influence of carbonaceous reinforcement (graphene oxide, GO) on the microstructural and mechanical properties of aluminum (Al) matrix composite fabricated by single-pass friction stir processing (FSP). GO reinforcement is introduced to the metal matrix by adhesively attaching GO powder to the surface of pure Al plates. The presence of GO within the Al matrix is initially characterized using Raman spectroscopy and secondary ion mass spectrometry, followed by detailed analysis using scanning electron microscopy and transmission electron microscopy. Due to dynamic recrystallization, significant grain refinement occurs in both FSP-treated Al alloys with and without GO conditions. However, the grains are more refined for FSP-GO condition, as the extent of dynamic recrystallization changed due to the dispersion of GO within the Al matrix. The presence of GO and its interaction with Al alloys during FSP develop superior mechanical properties (higher yield and tensile strength with greater ductility) compared to the BM and FSP-treated Al (FSP-only) conditions. The microhardness distribution shows the most hardened region on the advancing side of the stir zone, where the GO concentration is relatively high due to material flow occurring during FSP.

Influence of tool plunge depth and multiple passes on the microstructure, texture evolution and hardness of age-hardenable aluminium 7075 alloy

In this study, the surface properties of AA7075 were modified through the solid-state friction stir processing technique using a hexagonal-shaped H13 pin. Single pass friction stir processing was conducted at two different shoulder plunge depths at constant tool rotation and linear speeds with the resulting cross-sections being examined using optical macroscopy. Six friction stir processing passes were then carried out intermittently at optimal shoulder plunge depth and the corresponding microstructural evolution along the nugget was investigated using advanced microstructural characterization techniques such as electron backscatter diffraction and high-resolution transmission electron microscopy. Bulk texture examination was conducted using the neutron diffraction method, while hardness measurements were taken using Vicker's hardness testing machine. Single pass friction stir processing conducted at a shoulder plunge depth of 0.25 mm produced defect-free material consolidation with a refined grain structure along the nugget. Minimum grain size averaging 3.78 μm was observed at the top, while slightly increased grain sizes were noticed at the middle and bottom regions of the nugget. After 6 friction stir processing passes, grain size was reduced significantly averaging 1.84 μm at the top, while size at the pin-driven zone exhibited an increasing trend due to heat input and strain rate variations. Both, single-pass and 6 pass specimens exhibited a weaker texture along the nugget due to randomness in grain orientation and the effect of particle-stimulated nucleation mechanism. In the single-pass specimen, hardness decreased along the nugget, with a maximum of 85.2 HV at the top, while 6-pass specimen exhibited an improved hardness of 133.5 HV due to the strengthening caused by grain refinement, precipitates and dislocations.

Enhanced Mechanical Properties of Cast Cu-10 wt%Fe Alloy via Single-Pass Friction Stir Processing

In this study, Cu-10 wt% Fe alloy in as-cast state was modified using friction stir processing (FSP). The microstructure evolution of Cu-10 wt% Fe alloys in different states was characterized in detail using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that due to dynamic recrystallization, the FSPed Cu-10 wt% Fe alloy obtained a uniformly equiaxed ultrafine microstructure with low density of dislocation, high proportion of high-angle grain boundaries (HAGBs), and high degree of recrystallization. Fine equiaxed grains with an average size of 0.6 μm were produced after FSP. Many fine-precipitate Fe-phases with an average size of 20 nm were uniformly distributed in the Cu matrix. The FSPed samples possessed excellent mechanical properties, such as high Vickers hardness (163.5 HV), ultimate tensile strength (538.5 MPa), and good elongation (16%). This single-pass FSP method does not require subsequent aging treatment and provides a simple and efficient way to improve the properties of Cu-Fe alloys.

Rapid grain refinement and compositional homogenization in a cast binary Cu50Ni alloy achieved by friction stir processing

Friction stir processing (FSP) has been increasingly adopted for joining and processing materials in automotive, aerospace and industrial construction. During FSP a dynamic competition between high-speed shear deformation and deformation-induced heating brings about a complex competition between multiple dynamic microstructural evolution mechanisms making it difficult to predict the microstructural evolution pathway. Hence, improved understanding of microstructural evolution mechanisms during FSP can be beneficial for continued growth in the adoption of FSP for demanding applications of future. Towards this goal, this study uses a model binary Cu – 50 at.% Ni alloy to clarify the effect of single and double pass FSP on the microstructural evolution of a coarse grained and compositionally heterogeneous cast microstructure. High energy synchrotron X-ray diffraction, electron backscatter diffraction, and nanoindentation are used to clarify the microstructural evolution due to FSP. The process of compositional homogenization of as-cast segregations is studied by energy dispersive spectroscopy and atom probe tomography. Our results show that a single fast FSP pass at 30 mm.s−1 produces a 100 μm deep layer of submicrometric and hall-petch hardened CuNi grains. The initial cast compositional heterogeneities in a micrometric scale is rapidly transformed to nano-sized domains, mainly confined at grain boundaries. Double pass FSP increases the penetration depth of the processed layer and leads to a 2.9 times grain growth relative to single pass FSP. Grain fragmentation, discontinuous dynamic recrystallization, grain growth, and twinning mechanisms are discussed. These results highlight the value of FSP for ultrafast grain refinement and compositional homogenization of cast alloys.

Development of high strength and high electrical conductive Cu and Cu–W composite by friction stir processing: Effect of traverse speed

In this work, pure copper and copper-tungsten (Cu-W) surface composite is produced using a single pass friction stir processing (FSP) with an intention to enhance the hardness and wear resistance without impairing electrical conductivity. FSP is performed by changing the traverse speed from 50 to 200 mm/min and at a constant tool rotational speed of 600 rpm. The samples extracted from the stir zone are characterized for their microstructure, hardness, wear behaviour and electrical conductivity. The average grain size, at the stir zones, was significantly reduced (from 40 to 3 µm) after FSP. In the case of pure copper, the grain size decreased from 9 to 3 µm with an increase in traverse speed, however, grain size increased from 4 to 6 µm in the case of Cu-W composite. The hardness of FSP’ed Cu and FSP’ed Cu-W surface composite was increased in the order of 52% and 130% compared to the unprocessed copper. The wear rate significantly reduced after FSP also with an addition of W particles. A negligible reduction (1.83% IACS) in electrical conductivity was noticed for both Cu and Cu-W after FSP. This study demonstrates that the FSP is an effective approach to improve the surface mechanical properties of Cu without much impairing the electrical conductivity.

Effect of single-pass friction stir processing parameters on the microstructure and properties of 2 mm thick AA2524

Friction stir processing (FSP) is an important method for obtaining fine grains. To determine the effects of FSP and processing parameters on the microstructure and mechanical properties of rolled sheets, we performed single-pass FSP of a 2 mm thick 2524 aluminium alloy (AA2524) rolled sheet by comparing the combination of different processing parameters. The results show that lamellar grains (rolled state) are replaced by fine dynamic recrystallisation in the stir zone (SZ), and more Al2CuMg phases are precipitated simultaneously. As the rotation speed increases, the grain size and width of the pin stir zone (PSZ) increase, the microhardness first decreases and then increases; with the traverse speed increase, the grain size first decreases and then increases, and the width of the PSZ and microhardness decrease. The SZ has the smallest grain size, highest high-angle grain boundaries (HAGBs, with misorientation angles (θ) >15°) ratio, and largest ultimate tensile strength (UTS), when the rotation and traverse speed were 1000 r·min−1 and 125 mm·min−1, are 1.59 ± 0.82 μm, 0.91 and 451.23 ± 0.52 MPa, respectively, and the elongation to fracture is 13%. The UTS and elongation were only 95.12% and 98.48% of those of the base metals (BM), respectively, because of the significant decrease in the dislocation density. Fracture analysis revealed ductile fracture of the joint due to the large number of dimples and fine second-phase particles.

Optimization of friction stir processing parameters for enhanced microhardness of AA5083/Al-Fe in-situ composites via Taguchi technique

Friction stir processing (FSP) is a novel technique to fabricate metal matrix composites (MMCs) and surface composites (SCs). In the present study, Taguchi’s technique is used for attaining the optimum value of microhardness for AA5083/Al-Fe in-situ surface composites (SCs) via FSP using 40 hours mechanical alloyed Fe-40wt% Al powder mixture. Three different process parameters i.e. tool shoulder diameter, tool rotational speed, and tool traverse speed each having three levels were selected for optimizing the microhardness of SCs. The experimental study was accomplished by employing Taguchi's L9 orthogonal array. The Microhardness of the fabricated composites was confirmed using Vickers tester after the single-pass FSP. The outcomes of the study were examined and studied using signal to noise (S/N) ratio. The analysis also confirms the results and displayed that the optimum value of microhardness of 123.3 Hv was obtained with the selected parameter of tool shoulder diameter of 21 mm, tool rotational speed of 900 rpm, and traverse speed of 63 mm/min.

Microstructure, hardness, and wear resistance of AZ91 magnesium alloy produced by friction stir processing with air-cooling

Friction stir processing (FSP) was used to modify the surface layer of the AZ91 magnesium alloy. The treatment was carried out using a jet cooling nozzle, generating a stream of cold air and enabling intensive cooling of the friction stir processed (FSPed) zone. Single-pass FSP was carried out using a tool rotational speed of 500 rpm and travel speed of 30 mm/min. The treatment was conducted using a truncated cone-shaped tool with a threaded side surface. Strong grain refinement and microstructural changes typical for FSP were found in all the samples. Very fine, equiaxed recrystallized grains dominated in the stirring zone. In the samples modified with the jet cooling nozzle, greater grain refinement was obtained than in the case of naturally cooled material. The average grain size in the surface part of the stirring zone was 1.4 μm and 9 μm in the samples with air-cooling and with natural cooling, respectively. Both the naturally cooled specimen and air-cooled specimen were characterized by a distinctly higher hardness than the base material. The average Vickers hardness in the stirring zone was 91 HV0.1 in the FSPed sample with the air-cooling system and 85.5 HV0.1 with natural cooling, respectively. The average Vickers hardness of the as-cast alloy was 64 HV0.1. Slightly higher wear resistance of the FSPed samples using a jet cooling nozzle was found in relation to the naturally cooled sample. Based on the conducted research, high efficiency of the jet cooling nozzle in cooling the modified zone during friction stir processing was found.

Microstructure, mechanical and wear properties of friction stir processed Cu-1.0%Cr alloys

Abstract Friction stir processing (FSP) is a solid-state material processing technique to enhance the surface properties of metallic materials. In this study, Cu-1.0%Cr alloy is friction stir processed with an intention to improve its surface hardness and wear resistance. A single-pass FSP was performed by varying the tool traverse speed from 50 to 200 mm/min in steps of 50 mm/min and the tool rotational speed was kept constant at 600 rpm. Samples for microstructure, mechanical, electrical conductivity, and wear studies were extracted from the stir zone. The grain size of the stir zone was reduced to 4 μm from its initial 40 μm after processing with a traverse speed of 200 mm/min. An increase in hardness was observed in the stir zone processed with higher traverse speed (200 mm/min) from 71 HV to 95 HV. The minimum wear rate and decrease in coefficient of friction (CoF) were observed in the specimen processed with 200 mm/min. The electrical conductivity of the base alloy was 84.4 % IACS, whereas for the processed at 50 mm/min alloy it was 82.1 % IACS. Results showed that FSP is an effective way to increase the wear resistance of the surfaces without much deteriorating the electrical conductivity.

Effect of tool rotational speed on microstructure and mechanical properties of friction stir processed AA5083/Fe-Al in-situ composite

The formation of in-situ is the novel way to improvised the mechanical and metallurgical properties of the base metal. A groove made on the face of base metal was reinforced with reinforcement powder of Fe-Al. In this work, single-pass friction stir processing (FSP) was achieved on AA5083 using a cylindrical pin FSP tool having scroll on shoulder face. Mechanical and metallurgical inspections were performed at tool rotational speeds of 710, 900, and 1120 rpm. After FSP the grain refinement and a remarkable improvement in microhardness and UTS were observed. The maximum microhardness and UTS observed were 123.3 HV and 225.8 MPa respectively.

Effect of titanium carbide reinforcement on micro structure and wear properties of annealed AA6082 by friction stir processing

ABSTRACT Friction stir processing (FSP) has evolved as a novel solid-state technique to fabricate AA6082 plates in recent years. FSP technique was applied to analyse Aluminium Matrix Composites (AMC) AA6082 by reinforcing 6%–12% titanium carbide particles in the annealed state. A single-pass FSP was carried out using a tool with 1200 rpm rotational speed, whose travel speed of 60 mm/min and an axial force of 10 kN to produce the composite. The effect of its volume fraction of ingredient particles on the microstructure was studied using a Scanning Electron Microscopy (SEM). The results reveal that titanium carbide particles significantly influenced the grain size of the SEM images of the annealed AA6082 plates. The wear resistance shows improvement with an increase in weight per cent of titanium carbide particulates in the aluminium matrix.

Investigation of the hardening behavior during recrystallization annealing in Al-Mg-Sc alloy

In this work, Al-3Mg-0.2Sc alloy with a single pass friction stir processing (FSP) was cold rolled, followed by recrystallization annealing. Hardening behavior was observed in cold rolled alloy after annealing treatment at 330 °C and 400 °C. The hardening phenomenon can be rationalized by a calculation between the Zener pinning (PZ) and the driving force of recrystallization (PDRex). The result of contrastive calculation accords with the hardness change in the early stage of annealing, while the characteristics about coherency of Al3Sc particles determine that the contrastive calculation is inapplicable to later period of annealing. Specifically, the destruction of coherency between Al3Sc particles and matrix after annealing time exceeds 75 min makes that the actual value of PZ is much less than the predicted value of calculation.

Microstructure and texture evolution of complete Mg-3Al-0.2Ce alloy blanks upon multi-pass friction stir processing with spiral strategy

The objective of this study is to investigate the microstructure and texture evolution upon friction stir processing with multiple passes and spiral strategy, of Mg-3Al-0.2Ce alloy. Friction stir processing is a promising technique for grain refinement. Complete blanks of magnesium alloy are friction stir processed with all the combinations of two tool rotation speeds and two tool overlaps between passes. Optical microscopy, electron back scattered diffraction and texture analysis of the processed cross-sections are performed. Two distinct regions are observed in the processed blanks: banded region and non-banded region. Banded regions consist of much smaller grains as compared to the non-banded regions. The banded regions appear regularly at a distance corresponding to the tool overlap. The banded regions become more prominent at higher tool rotation speed and tool overlap. For the samples processed with higher tool overlap, the difference in grain sizes of banded and non-banded regions is significant, and interfaces between banded and non-banded regions are easily noticeable, which suggests bimodal microstructure. A tilted basal texture is revealed for all the processed samples. This is different from the oppositely tilted basal texture observed from the single pass friction stir processing of magnesium. The difference is attributed to the presence of resulting microstructure from both advancing and retreating side upon single pass friction stir processing. While for multi-pass friction stir processing with spiral strategy, the microstructure resulting from retreating side alone is present in the processed blanks. The close packing of similar microstructure from retreating sides of successive passes also led to higher texture index.

Experimental investigation of bending and tensile strength of friction stir processed TIG-welded AA5083-H111 joint

This paper reports on the experimental investigation of bending and tensile strength of the friction stir processed TIG-welded AA5083-H111 joint. The friction stir processed joint was studied comparatively with the TIG-welded joint (unprocessed joint). The TIG-welded joint was processed using a single-pass friction stir processing technique. The microstructural analysis revealed that the unprocessed joint was dominated with coarse grains while the refined grains dominated the friction stir processed joint. The unprocessed joint consistently failed at the center of the joint during tensile testing while the processed joint failed in different locations of the stir zone. The tensile strength of the unprocessed joint was found to be 47.4% to that of the base metal while that of the processed joint was found to be 76.5% to that of the base metal. The percentage elongation of the processed joint was found to be 82.4% to that of the base metal while that of the unprocessed joint was found to be 34.8% to that of the base metal. The bending failure mode of the processed and unprocessed joint was similar to that observed during tensile testing.

Mechanical properties enhancement of cast Al-8.5Fe-1.3V-1.7Si (FVS0812) alloy by friction stir processing

This study was conducted to investigate the capability of multi-pass friction stir processing (FSP) on microstructure modification and mechanical properties improvement of FVS0812 alloy. FSP was performed at different rotation speeds (1250, 1600, 2000, and 2500 rpm) and traverse speeds (8, 12, and 25 mm/min) for one, two, and four passes. According to the results, applying single-pass FSP at optimized conditions (i.e. 1600 rpm and 12 mm/min) enhanced the tensile strength, fracture strain, and microhardness of the alloy by about 1020, 1050, and 60%, respectively. This improvement can be mainly attributed to the intense breakage and uniform distribution of θ-Al13Fe4 and α-Al12(Fe,V)3Si intermetallics within the matrix, formation of ultrafine recrystallized grains, and elimination of casting defects. Increasing the number of FSP passes up to four slightly decreased the average size of intermetallic particles, but significantly improved their distribution within the matrix which led to 18 and 200% improvement of tensile strength and fracture strain of one-pass FSPed sample, respectively. The fractography results also revealed that multi-pass FSP has changed the fracture mode of Al-8.5Fe-1.3V-1.7Si alloy from low-energy brittle to a more ductile-dimple fracture.

Characterization of aluminium / (SiC+B4C) ceramic particles reinforced hybrid Surface Composites (SC) fabricated by friction stir processing

Friction stir processing (FSP) has advanced as a novel method used for the fabrication of surface composite (SC), refinement of microstructure and enhancing the mechanical properties. In this paper, aluminium surface matrix composite (SMC+ B4C) was fabricated on the surface of aluminium alloy (6082) with ceramic (SiC+B4C) reinforcement using friction stir processing technique. In order to analyse the effect of SiC+B4C particles, its percentage fraction on the microstructure, mechanical and the sliding wear behaviour. A single pass FSP was carried out using a tool with 1000 - 1200 rpm rotational speed, whose travel speed of 45 to 60 mm/min and a vertical force to produce the composite. Aluminium Matrix Composites with different percentile combinations were synthesized. The microstructure of the AA6082/SiC+B4C AMCs was studied using optical and scanning electron microscopy. The micro hardness was measured and the sliding wear behaviour was evaluated using a pin-on-disc apparatus. Thus, the results revealed that the effect of SiC+B4C particles significantly influenced the area of the composite, dispersion, grain size of matrix, micro hardness, and sliding wear behaviour of the AA6082/SiC+B4C AMCs. With this the effect of SiC+B4C particles on fracture surface and worn surface is also reported in this paper.

Fatigue behaviour of the multi-pass friction stir processed AA8011-H14 and AA6082-T651 dissimilar joints

The AA8011-H14 and AA6082-T651 were used to produce dissimilar joint through the use of friction stir welding (FSW) technique. The produced dissimilar joint was processed using multi-pass friction stir processing (FSP). The microstructural analysis revealed that the grain sizes reduced with an increase in the number of FSP passes irrespective of material positioning. However, the multi-pass AA6082-AA8011 joints had finer grain structure compared to the multi-pass AA8011-AA6082 one. The ultimate tensile strength of the multi-pass FSP had an increase of 11.6% compared to that of the single-pass one, but only for the AA8011-AA6082 joints, while the AA6082-AA8011 had an increase of 9% on the two-pass FSP. The number of FSP passes was found to have a marginal effect on the microhardness of the joints. The two-pass FSP joints were found to be more ductile compared to the other passes. The fatigue results revealed that the AA6082-AA8011 joints had longer fatigue life compared to that of the AA8011-AA6082 joints. The increase in the number of FSP passes increased the fatigue life of the AA8011-AA6082 joints, while AA6082-AA8011 joints experienced extended fatigue life cycle on the single-pass FSP.

Texture transition in friction stir processed Al powder compact

Green Al powder compacts of commercial purity with random orientation were subjected to single pass friction stir processing (FSP) with different tool rotational and traverse speeds. The evolution of crystallographic texture obtained from large area electron back scattered diffraction were compared with the bulk texture of the nugget zone characterized using synchrotron diffraction. Evolution of different deformation and recrystallization texture components were discussed. While the grain size distributions were found to be independent of process parameters, the texture components and their strength of the FSPed samples were strongly influenced by the process parameters. Continuous dynamic recrystallization (CDRx) was found to be the primary restoration mechanism for most of the processing conditions leading to a bi-modal misorientation distribution. The possible relations between different texture components and the appearance or suppression of bimodal misorientation distributions were discussed. Restoration mechanism changed to discontinuous dynamic recrystallization (DDRx) with the evolution of cube component at the stir zone along with random misorientation distribution. Dominance of a particular restoration mechanism depends on strain, strain rate and temperature attained during the processing.

Development of high strength and high electrical conductivity Cu/Gr composites through friction stir processing

The Copper/Graphene (Cu/Gr) composite was prepared with single-pass friction stir processing. The composites were prepared by fixing the tool rotational speed and by varying the traverse speed. The stir-zone of processed specimens were characterized for its microstructure, hardness and electrical conductivity. Microstructural investigation showed that graphene has uniformly distributed in the Cu-matrix. The hardness increased by up to 40% after FSP. A minimal decrease in electrical conductivity was observed after friction processing. The study showed FSP is a promising method to improve the mechanicalproperties of Cu without much deterioration in electrical conductivity.

The effect of friction stir processing on the friction stir welded AA1050-H14 and AA6082-T6 joints

In this paper, the single-pass friction stir processing technique was applied to the friction stir welded dissimilar aluminium joints. This was done to create a comparative analysis of the mechanical properties of the friction stir processed FSW and unprocessed FSW welded joints of the AA1050-H14 and AA6082-T6 where different positioning (advancing and retreating) were used to assess which positioning gives better mechanical properties. A rotational speed of 1200 rpm, traversing speed of 40 mm/min and a tool tilt of 2° were used as for both friction stir welding and friction stir processing. The tests conducted include tensile tests, microstructure, microhardness. The fracture surfaces of tensile testing were further analysed using the scanning electron microscopes (SEM) with Oxford energy-dispersion spectrometry (EDS). The Ultimate tensile strength of 83.2 MPa, percentage elongation of 22.13% and yield strength 61.1 MPa were found on the friction stir processed joint. The friction stir processed joint also had a maximum microhardness of 80HV which was higher than that of the unprocessed one. The results show that FSP resulted in the improvement of the mechanical properties due to the grain size refinement. The positioning of aluminium alloy 1050-H14 on the advancing side and AA6082-T6 on the retreating side yielded better results for both unprocessed friction stir welded joints and friction stir processed joints.