Two-pass Friction Stir Processing Research Articles

Development and characterization of AZ91/AlN magnesium matrix composites via friction stir processing

Magnesium AZ91/AlN-based surface composites have been synthesized using the friction stir processing (FSP) technique. The influence of particle addition during FSP on microstructural and mechanical properties has been investigated. Composite plates of 5, 10, and 15 vol. % AlN were synthesized using two-pass FSP with an axial force of 10 KN, a tool travel speed of 40 mm/min, and a tool rotation speed of 1200 rpm. The AZ91/AlN surface composites were analyzed microscopically with the use of an optical microscope, an x-ray diffractometer, and a scanning electron microscope. The prepared composites were tested for hardness and tensile strength. Micrographs taken in the stir zone revealed a consistent distribution of AlN particles throughout the AZ91 matrix. The AZ91/AlN surface composites were tested for hardness and tensile strength, and the findings showed that the AlN particles improved the mechanical properties without significantly decreasing ductility. The fracture surfaces of the composites were studied, and the mechanisms of fracture were identified.

Evaluating the influence of various friction stir processing strategies on surface integrity of hybrid nanocomposite Al6061

To fundamentally investigate the influence of different friction stir processing (FSP) strategies, namely raster, spiral, and parallel in various passes on the surface integrity of hybrid aluminum nanocomposites reinforced by titanium oxide (TiO2), silicon carbide (SiC), and zirconium oxide (ZrO2) nanoparticles, various examinations were conducted. The surface integrity, comprising microstructural characterization, elemental composition, surface topography, roughness, waviness, and microhardness was studied by different analyses, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), optical microscopy (OM), atomic force microscopy (AFM), and Vickers microhardness machine in different zones. Results demonstrated that surface integrity and quality are dependent on the type of FSP strategy. SEM images revealed that a homogeneous distribution of the nanoparticles in the matrix is obtainable by the parallel and raster FSP strategies. Roughness and waviness measurements illustrated that the surface topography of the hybrid nanocomposite was symmetrical and improved by raster strategy and TiO2 + ZrO2 nanoparticle reinforcement. Furthermore, the two-pass FSP improved the arithmetic average surface value (Ra) such that the Ra of two passes decreased by 32.5% compared to a single one. The mean microhardness in the spiral, raster, and parallel pass strategies increased by ~ 45%, 37%, and 31%, respectively.

Microstructure and Properties of Aluminum-Graphene-SiC Matrix Composites after Friction Stir Processing.

Enhancing the mechanical properties of conventional ceramic particles-reinforced aluminum (Al 1060) metal matrix composites (AMCs) with lower detrimental phases is difficult. In this research work, AMCs are reinforced with graphene nanosheet (GNS) and hybrid reinforcement (GNS combined with 20% SiC, synthesized by shift-speed ball milling (SSBM), and further fabricated by two-pass friction stir processing (FSP). The effect of GNS content and the addition of SiC on the microstructure and mechanical properties of AMCs are studied. The microstructure, elemental, and phase composition of the developed composite are examined using SEM, EDS, and XRD techniques, respectively. Mechanical properties such as hardness, wear, and tensile strength are analyzed. The experimental results show that the GNS and the SiC are fairly distributed in the Al matrix via SSBM, which is beneficial for the mechanical properties of the composites. The maximum tensile strength of the composites is approximately 171.3 MPa in AMCs reinforced by hybrid reinforcements. The tensile strength of the GNS/Al composites increases when the GNS content increases from 0 to 1%, but then reduces with the further increase in GNS content. The hardness increases by 2.3%, 24.9%, 28.9%, and 41.8% when the Al 1060 is reinforced with 0.5, 1, 2% GNS, and a hybrid of SiC and GNS, respectively. The SiC provides further enhancement of the hardness of AMCs reinforced by GNS. The coefficient of friction decreases by about 7%, 13%, and 17% with the reinforcement of 0.5, 1, and 2% GNS, respectively. Hybrid reinforcement has the lowest friction coefficient (0.41). The decreasing friction coefficient contributes to the self-lubrication of GNSs, the reduction in the contact area with the substrate, and the load-bearing ability of ceramic particles. According to this study, the strengthening mechanisms of the composites may be due to thermal mismatch, grain refinement, and Orowan looping. In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of the composites.

Optimization of friction stir processing parameters for improving structural and mechanical properties in in situ AA5083-H111/Al–Fe composites

The primary focus of this study is the application of friction stir processing to produce surface composites of in situ AA5083-H111/Al–Fe. These composites were fabricated by mixing mechanically alloyed Fe–40 wt% Al powder for 40 h. The AA5083 substrate underwent a two-pass friction stir processing with changes in the tool’s movement direction during fabrication. This experiment used Taguchi’s L9 orthogonal array design to gather and analyse data efficiently. Following each friction stir processing pass, the fabricated aluminium metal matrix composite microstructure, hardness and ultimate tensile strength were conducted. In this study, the maximum tensile strength of 225.8 MPa after the first pass and 253.6 MPa after the second pass. Additionally, microhardness measurements indicated values of 123.3 and 128.3 Hv after the first and second passes, respectively. These impressive mechanical properties were achieved by optimizing specific process parameters, including a tool shoulder diameter of 21 mm, a tool rotational speed of 900 rpm, a tool traverse speed of 63 mm/min and a tilt angle of 1.5°. Furthermore, examining the fracture surface of the friction stir processed sample revealed ductile failure behaviour, suggesting that the material experienced deformation and stretching before fracture. This observation aligns with the inherent ductile nature of the AA5083/Al–Fe composite.

A study on the metallurgical characterisation of the longitudinally sampled friction stir processed TIG welded dissimilar aluminum joints

In this work, one-pass and two-pass friction stir processing (FSP) were applied to the tungsten inert gas (TIG) weldments of AA6082-T651 and AA8011-H14 to analyse the microstructure and tensile characteristics of the weldments. The tests included macrostructure, microstructure, microhardness, tensile testing and fractography. When the one-pass and two-pass FSP were applied to the TIG weldments, the coarse grain structure (grain size 24.63 µm) was transformed into a refined grain structure (grain size 2.632 µm for second pass), thereby eradicating the defects that had been seen before FSP. The tensile strengths of the TIG + FSP passes were more significant than that of the TIG welded joints. The ultimate tensile strength of TIG welding, TIG + FSP 1-pass and TIG + FSP 2-pass were 86.86 MPa, 133.833 MPa and 135.75 MPa, respectively. The tensile strain of the TIG + FSPed joints was found to have a minimal difference from that of the TIG welded joints, with the TIG joint with a higher percentage. The joints’ microhardness post-FSP was more significant than the TIG weldment. The maximum hardness (73.84 HV) at the Nugget zone (NZ) was observed in the TIG + FSP 2-pass welded joint. The results obtained corresponded with the grain sizes of the welded joints; the TIG results displayed a coarse-grained structure, while the TIG + FSP results, regardless of the passes, showed a fine sandwich-arranged grain structure.

Effect of multi-pass friction stir processing on the microstructure evolution and corrosion behavior of ZrO2/AZ31 magnesium matrix composite

Most of magnesium matrix composites processed by traditional technique have poor anti-corrosion and biological performance, because of uneven microstructure, especially for nonuniform distribution of reinforced particles. Friction stir processing (FSP) can be used for preparing magnesium matrix composites with refine grains and uniform distribution of reinforced particles. In this paper, multi-pass FSP is employed to fabricate the ZrO2 particles reinforced AZ31 magnesium composites. The results showed that the microstructure of the composites become more homogeneous with the increase of FSP pass. The grain size is refined from 10 μm of basal metal (BM) to 8.2 μm of two-pass FSP (FSP-2P) and 4.5 μm of four-pass FSP (FSP-4P), respectively. The ultimate tensile strength, yield strength and elongation of BM is 283 MPa, 137 MPa and 15.5%. The mechanical properties are improved with the increase of FSP pass. The ultimate tensile strength, yield strength and elongation of FSP-4P is 328 MPa, 160 MPa, and 11.5%, respectively. Moreover, the corrosion resistance is arranged in the following order: FSP-2P < BM < FSP-4P. The cell activity of FSP-4P is higher than that of FSP-2P sample, which is similar to BM.

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.

Effect of multi-pass friction stir processing on thermal distribution and mechanical properties of AZ91

In this paper, the effect of multi-pass friction stir processing on mechanical properties of AZ91 alloy has been studied. For this purpose, the microhardness, tensile, and creep tests were conducted at several temperatures. Optical microscopy and scanning electron micrograph were used to study the microstructure of the processed samples. The experimental results indicated that at room temperature, the microhardness, tensile, and creep strength of the processed samples as compared to the unprocessed ones increased by 23%, 29%, and 38%, respectively. Also, after friction stir processing, the tensile and creep strength of the samples at 210 °C increased by 31% and 47%. In addition, a three-dimensional model was developed to simulate two-pass friction stir processing using ABAQUS/Explicit software. This model involved the Johnson-Cook models for defining material behavior during the process and identifying the fracture criterion. To control the mesh distortion during consecutive passes, the Arbitrary Lagrangian-Eulerian technique was used. Using the developed model, the peak temperature, thermal distribution, and residual stress field during multi-pass friction stir processing on AZ91 have been studied. The empirical results indicated the beneficial influence of the multi-pass friction stir processing on the microstructure and high-temperature mechanical properties of AZ91 alloy.

Microstructure and Properties of Nano-Hydroxyapatite Reinforced WE43 Alloy Fabricated by Friction Stir Processing.

This research mainly focuses on the successful fabrication of nano-hydroxyapatite (nHA) reinforced WE43 alloy by two-pass friction stir processing (FSP). Microstructure evolution, mechanical properties, and in vitro corrosion behavior of FSPed WE43/nHA composite and FSPed WE43 alloy were studied. The results show that nHA particles are effectively dispersed in the processing zone, and the well-dispersed nHA particles can enhance the grain refine effect of FSP. The average grain sizes of FSPed WE43 alloy and WE43/nHA composite are 5.7 and 3.3 μm, respectively. However, a slight deterioration in tensile strength and yield strength is observed on the WE43/nHA composite, compared to the FSPed WE43 alloy, which is attributed to the locally agglomerated nHA particles and the poor quality of interfacial bonding between nHA particles and matrix. The electrochemical test and in vitro immersion test results reveal that the corrosion resistance of the WE43 alloy is greatly improved after FSP. With the addition of nHA particles, the corrosion resistance of the WE43/nHA composite shows an even greater improvement.

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

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

The Effect of Processing Pass on the Microstructure and Mechanical Properties of a Friction Stir Processed As-Cast Mg-6 wt % Sn Alloy

In this study, as-cast Mg-6 wt % Sn alloy is subjected to one-pass and two-pass friction stir processing (FSP). The effect of processing pass on microstructure and mechanical properties of FSP Mg-6Sn alloy is investigated. It is found that one-pass FSP leads to the breakage and partial dissolution of the Mg2Sn phase in the stir zone (SZ) and two-pass FSP leads to the further dissolution and dynamic precipitation of the Mg2Sn phase. Dynamic recrystallization (DRX) takes place in the SZ of an Mg-6Sn alloy undergoing FSP. Compared to one-pass FSP, two-pass FSP brings about further grain refinement in the SZ. A strong {0001} basal texture is developed in the SZ of a Mg-6Sn alloy from FSP and the change of the sample region or processing pass has little influence on the texture. Compared to an as-cast Mg-6Sn sample, one-pass FSP brings about significant improvement in mechanical properties. Two-pass FSP leads to the further increase in yield strength (YS) and ultimate tensile strength (UTS) but elongation (EL) is reduced. The continuous increase in strength is attributed to the grain refinement and the dissolution and dynamic precipitation of Mg2Sn phase achieved by FSP.

Effect of First and Second Passes on Microstructure and Wear Properties of Titanium Dioxide-Reinforced Aluminum Surface Composite via Friction Stir Processing

The dispersion of particles in polymer, ceramic and metal matrix composites via conventional routes was very difficult, due to agglomeration/clustering of particles, poor compatibility of properties of particle and matrix. So, an attempt has been made to uniformly disperse the titanium dioxide particles on the surface of aluminum matrix via two-pass friction stir processing. The effect of passes on particle distribution, microstructure, microhardness and wear properties was systematically investigated. Microstructural studies revealed a fine equiaxed grain structure in the stir zone due to the dynamic recrystallization. The first-pass surface composite sample results in agglomeration of particles toward the advancing side due to insufficient materials flow and strain. The second pass was carried out by changing advancing and retreating side of composite plate processed by the first pass. The results showed that marginal change in grain size was observed with homogeneous microstructure when compared to first-pass surface composite. Microhardness was carried out across the cross sections of the surface composites to obtain hardness profile. The tribological performance was assessed using a pin-on-disk tribometer. The result reveals that surface composites processed by the second pass show better hardness and wear resistance when compared to as-received aluminum. The wear mechanism shows a transition from adhesive wear in surface composites to the combination of abrasive and delamination wear in as-received aluminum.

Microstructures and mechanical properties of AZ91 alloys prepared by multi-pass friction stir processing

Abstract

Microstructure Evolution and Mechanical Properties of AZ61 Mg Alloy Processed by Two-Pass Friction Stir Processing

Friction stir processing (FSP) has been considered as a promising technique for grain refinement. In this study, two-pass FSP was conducted under water to enhance the cooling rate during processing, and a fine-grained AZ61 magnesium alloy was prepared through this method. Compared with one-pass FSP, the microstructure of two-pass FSP alloy is more homogeneous and finer, with an average grain size of 1.8 μm. Both the tensile strength and ductility of the two-pass FSP sample are improved due to grain refinement. A tensile elongation of 31.8% was achieved in the two-pass FSP sample. The microstructure evolution mechanism during the processing was discussed based on the microstructure examination.

Microstructure and Mechanical Properties of ZK60 Magnesium Alloy Prepared by Multi-Pass Friction Stir Processing

Friction stir processing (FSP) is a novel severe plastic deformation technique developed in recent years to produce fine-grained structural materials. In this paper, the microstructure and mechanical properties of ZK60 magnesium alloy prepared by the single-pass and two-pass FSP were studied. The first-pass was subjected with 800r/min-100mm/min and the second-pass was subjected with 600r/min-100mm/min. The results show that the coarse second phase was dissolved into magnesium matrix and the α-Mg grains were remarkably refined in stir zone after FSP. The average grain sizes of the single-pass and two-pass FSP alloys were 6.8μm and 6.0μm respectively. The microhardnesses of the specimens were 70HV and 65HV, the ultimate tensile strengths were 276MPa and 272MPa, and the elongations were 31.6% and 42.5%, respectively. Through increasing the processing pass, the microstructure became finer and the second phase is dissolved more thoroughly. The combined effect of grain refinement and second phase dissolved was responsible for the change of mechanical properties.

Ductility Improvement of an AZ61 Magnesium Alloy through Two-Pass Submerged Friction Stir Processing.

Friction stir processing (FSP) has been considered as a novel technique to refine the grain size and homogenize the microstructure of metallic materials. In this study, two-pass FSP was conducted under water to enhance the cooling rate during processing, and an AZ61 magnesium alloy with fine-grained and homogeneous microstructure was prepared through this method. Compared to the as-cast material, one-pass FSP resulted in grain refinement and the β-Mg17Al12 phase was broken into small particles. Using a smaller stirring tool and an overlapping ratio of 100%, a finer and more uniform microstructure with an average grain size of 4.6 μm was obtained through two-pass FSP. The two-pass FSP resulted in a significant improvement in elongation of 37.2% ± 4.3%, but a slight decrease in strength compared with one-pass FSP alloy. Besides the microstructure refinement, the texture evolution in the stir zone is also considered responsible for the ductility improvement.

Microstructure and Mechanical Properties of a Fine-Grained AZ91 Magnesium Alloy Prepared by Multi-Pass Friction Stir Processing

Friction stir processing (FSP) is a novel severe plastic deformation technique developed in recent years to produce fine-grained structural materials. Through increasing the processing pass, further grain refinement can be achieved. In this paper, the microstructure and mechanical properties of AZ91 magnesium alloy prepared by the single-pass and two-pass FSP were studied. The results showed that the coarse, network-like eutectic β-Mg17Al12 phase was broken into particles and some of them dissolved into the magnesium matrix, and the α-Mg grains were remarkably refined after FSP. The average grain sizes of the single-pass and two-pass FSP alloys were 8.3 μm and 5.8 μm respectively. The ultimate tensile strengths of the specimens were 284.5 MPa and 319.7 MPa, and elongations were 13% and 14.5%, respectively. The improved mechanical properties of the two-pass FSP specimen were mainly attributed to the finer grain size and more homogenized microstructure.

Enhanced mechanical properties of tungsten inert gas welded AZ31 magnesium alloy joint using two-pass friction stir processing with rapid cooling

In this study, tungsten inert gas (TIG) welded AZ31 magnesium alloy joint was subjected to two-pass rapid cooling friction stir processing (RC-FSP). The main results show that, two-pass RC-FSP causes the significant dissolution of the coarse eutectic β-Mg17Al12 phase into the magnesium matrix and the remarkable grain refinement in the stir zone. The low-hardness region which frequently located at heat-affected zone was eliminated. The stir zone showed ultrafine grains of 3.1μm, and exhibited a good combination of ultrahigh tensile strength of 284MPa and large elongation of 7.1%. This work provides an effective strategy to enhance the strength of TIG welded magnesium alloy joint without ductility loss.

Effect of two-pass friction stir processing on the microstructure and mechanical properties of as-cast binary Al–12Si alloy

The effect of two-pass friction stir processing (FSP) on the microstructural evolution, mechanical properties and impact toughness of as-cast Al–12Si alloy was investigated systematically. Severe plastic deformation imposed by FSP resulted in a considerable fragmentation of the needle-shaped eutectic silicon particles into the smaller ones. The length of eutectic Si particles decreased from 27±23μm to about 2.6±2.4μm. The average aspect ratio of 6.1±5.1 for eutectic Si particles in the as-cast state decreased to about 2.6±1.0 after FSP with a corresponding increase in their roundness. The hardness, strength, ductility and impact toughness of the alloy increased simultaneously after two-pass FSP. The increase in the yield and tensile strength values after FSP was about 20% and 29%, respectively. The FSPed alloy exhibited 25% elongation to failure and 15% uniform elongation which were almost seven times and five times higher, respectively, than those of the as-cast alloy. The hardness of the alloy increased from 58 Hv0.5 for the as-cast state to about 67 Hv0.5 after FSP. The absorbed energy during impact test increased to about 8.3J/cm2 after FSP, which is about seven times higher than that of the as-cast alloy. Improvements in all mechanical properties were mainly attributed to the radical changes of the shape, size and distribution of the eutectic silicon particles along with the breakage and refined of the large α-Al grains during two-pass FSP.

Achieving High Strength and High Ductility in Friction Stir-Processed Cast Magnesium Alloy

Friction stir processing (FSP) is emerging as an effective tool for microstructural modification and property enhancement. As-cast AZ91 magnesium alloy was friction stir processed with one-pass and two-pass to examine the influence of processing conditions on microstructural evolution and corresponding mechanical properties. Grain refinement accompanied with development of strong basal texture was observed for both processing conditions. Ultrafine-grained (UFG) AZ91 was achieved under two-pass FSP with fine precipitates distributed on the grain boundary. The processed UFG AZ91 exhibited a high tensile strength of ~435 MPa (117 pct improvement) and tensile fracture elongation of ~23 pct. The promising combination of strength and ductility is attributed to the elimination of casting porosity, and high density of fine precipitates in an UFG structure with quite low dislocation density. The effects of grain size, precipitate, and texture on deformation behavior have been discussed.