Friction Stir Processing Passes Research Articles

Multipass Friction Stir Processing of Steel/SiC Nanocomposite: Assessment of Microstructure and Tribological Properties

A surface layer of steel/SiC nanocomposite was fabricated by multiple passes of friction stir processing (FSP) on a low-carbon steel. The characterization methods such as optical microscopy, field emission scanning electron microscopy, microhardness, and wear test were performed to obtain the microstructure and mechanical properties of the produced layers. The results revealed that the dispersion of nano-SiC particles is directly related to the FSP passes and that the superior scattering of the nanosized SiC particles is achieved at higher FSP passes. Nano-composite surface layers demonstrated an average microhardness value of ~ 424 HV, which is ~ 3.4 times higher than that of the as-received substrate. Moreover, ultra-fine submicron grains were formed by FSP due to the role of SiC particles as obstacles to grain growth. The produced surface-layer nanocomposite exhibited an outstanding enhancement in wear resistance in comparison with the FSPed sample without reinforcing particles.

Characterization of aluminum based functionally graded composites developed via friction stir processing

Abstract Al/SiC functionally graded material (FGM) was developed through a novel multi-step friction stir processing (FSP) method. SiC particles with a mean size of 27.5 μm were embedded in the groove on the 6082-Al plate. To create a graded structure over a predefined value, FSP was carried out with three tools with different pin lengths and with varying volume fractions of SiC particles. The structure was formed by passing tools with 1−3 passes with a constant rotational and traveling speeds of 900 r/min and 20 mm/min, respectively. The experiments were conducted at room temperature. Microstructural features of functionally graded (FG) samples were examined by using scanning electron microscopy (SEM) and 3D light microscopy. Mechanical properties in terms of wear resistance and microhardness were thoroughly assessed. The results indicate that the increase in FSP pass number causes more uniform SiC particle dispersion. The microhardness values were impacted by the number of passes and improved by 51.54% for Pass 3 when compared to as-received 6082-Al. Wear resistance of Al/SiC FG samples was found to increase as a result of the addition of SiC particles.

Enhancing the mechanical and tribological properties of Mg2Si-rich aluminum alloys by multi-pass friction stir processing

Particle strengthening of in-situ Al-Mg2Si composites hinges on effective geometrical parameters (size, distribution, morphology, and volume fraction) of the inherent primary Mg2Si particles. The use of solid-state friction stir processing (FSP) in a multi-pass mode is recognized as a secondary processing route capable of achieving desirable geometrical parameters of Mg2Si particles in Al-Mg2Si composites as compared to other routes. This paper thus studies the microstructure, mechanical properties, and tribological behavior of the multi-pass FSPed in-situ Al-25Mg2Si composite with a threaded triangular pin tool. The FSP was conducted at constant tool rotational and traverse speeds of 1000 rpm and 80 mm/min for 1–6 passes. The results showed a decline in the average Mg2Si size (115–3.25 μm), porosity content (5.8–0.14%), and primary Mg2Si particle-depleted region as the FSP passes are increased (0–6). Improved geometrical parameters of the primary Mg2Si particles enhance microhardness (178–272 HV), tensile strength (102–233 MPa) and wear resistance of the Al-25%Mg2Si composite via particle dispersion and dislocation strengthening effects, grain refinement, and microstructural densification. Multi-pass FSP can be adopted as a better substitute to element addition, casting modification, heat treatment and electromagnetic stirring in effectively controlling the geometrical parameters of the primary Mg2Si in in-situ Al-Mg2Si composites for improved mechanical and tribological properties.

Microstructure and Tensile Properties of SiC Particles Reinforced AZ31 Magnesium Alloys Prepared by Multi-pass Friction Stir Processing

Two different sized SiC particles (~ 60 nm and ~ 1 μm) were mixed into AZ31 alloy by multi-pass friction stir processing (FSP). The microstructure and mechanical properties of the processed material were investigated by optical microscope, scanning electron microscope, and uniaxial tensile tests. After FSP without SiC addition, the grains were refined to several microns. The elongation was improved significantly after processing, at an expense of significant sacrifice in yield strength. 60 nm SiC particles were composited homogeneously in the matrix by four passes of FSP to enhance the yield strength. The yield strength exhibited a 68% improvement which could well compensate the decreased yield strength in FSP without SiC addition. In addition, the 1 μm SiC particles were inhomogeneous in the stir zone which also induced an increase in yield strength. However, the elongation decreased sharply because cracks nucleated and propagated quickly at the SiC–matrix interface.

Effects of pin diameter and number of cycles on microstructure and tensile properties of friction stir fabricated AA1050-Al2O3 nanocomposite

Nanocomposites of Al-Al2O3 are fabricated by means of friction stir processing (FSP). Effects of pin diameter and number of FSP cycles on tensile properties of the nanocomposites are investigated and the variations are correlated to the evolution of microstructure and distribution of nanoparticles in addition to agglomeration of Al2O3 nanoparticles. Investigation of agglomeration has been considered as an indirect indication for efficiency of the process for distribution of nanoparticles. The ductility of the nanocomposite is found to improve due to grain refinement during FSP. However, the ductility is likely to degrade if Al2O3 particles agglomerate and form coarse particles. The composite fabricated using the 6-mm pin indicates the maximum ductility which is attributed to formation of fine grain structure and efficient distribution of nanoparticles in the composite. Although, the grain structure in the composite fabricated using 8-mm pin is well refined, this sample shows significantly lower ductility with respect to the other samples. This was attributed to formation of coarse agglomerated particles. The second pass of FSP is found to slightly improve ductility and strength in composites fabricated using 4- and 6-mm pins but enforce significant improvements in the one with 8-mm pin. This is indeed because the second pass results in significant change in the distribution of nanoparticles or agglomerated particles in the latter case and negligible in the former ones. Grain structure and nanoparticle distribution and agglomeration can all affect the fracture surface of the tensile specimens of the fabricated nanocomposite to be ductile or brittle.

Microstructural and mechanical characteristics of AA1050/mischmetal oxide in-situ hybrid surface nanocomposite by multi-pass friction stir processing

Surface hybrid in-situ aluminum matrix nanocomposite (AMNC) was fabricated by multi-pass friction stir processing (FSP) and a tool traversing speed of 100 mm/min and rotating speed of 1600 rpm with an objective to enhance mechanical properties. Mischmetal oxide (MMO) powder with an initial size of 50 nm, at a concentration of 8.5 vol% was used as the reinforcing particles. EDS particle analyses revealed in-situ solid-state chemical reactions between the Al matrix and the MMO particles. The reaction products, MM3Al and MM3Al11, were distributed uniformly in the discontinuously dynamic recrystallized nano and UFG microstructure. Increasing pass number improved the particle distribution and decreased agglomerated particle size while promoting the in-situ solid-state reaction. The nanocomposite produced by 6 FSP passes enhanced yield stress, 180% (YS = 70 MPa) and strength, 120% (UTS = 132 MPa) while reduced the tensile ductility from 35% to 23%. Fractographic studies showed that dimple-shape ductile fracture mode changed to ductile-brittle mode.

Effect of SiC Particles on Microstructure and Wear Behavior of AA6061-T6 Aluminum Alloy Surface Composite Fabricated by Friction Stir Processing

This research studies the effect of SiC particles on the microstructure and wear behavior of AA6061-T6 aluminum alloy surface composite. Friction stir processing (FSP) was used to incorporate micro-sized SiC particles into AA6061-T6 aluminum alloy to form a particulate composite surface layer. Samples were subjected to two passes of FSP with and without SiC powder at the best rotational speed of 1250 rpm, travel speed of 32 mm/min and two passes in the same direction. Microstructural observations were conducted via optical and scanning electron microscopy (SEM) of samples subject to FSP. Mechanical properties, including microhardness and wear resistance, were evaluated. The results manifested that at two passes, the FSP caused a more uniformity in the distribution of SiC particles. The addition of SiC particles to AA6061-T6 improved the hardness (improvement 62.6%) and wear resistance as compared to FSPed sample without SiC particles. The wear behavior was of a mild type or an oxidative type at low loads (5 N), which became severe or metallic wear at higher loads (20 N) for sliding time 20 min.

An investigation of microstructure, wear and corrosion resistance of AZ31B–SiO2–graphite hybrid surface composite produced by friction stir processing

Magnesium-based hybrid composites are light and have better mechanical and tribological properties than magnesium. In this research, AZ31B–SiO2–graphite hybrid surface composite was produced by multipass friction stir processing (FSP). The effect of FSP passes on microstructure, microhardness, wear resistance, and corrosion resistance of the composite was investigated and compared with friction stir processed (FSPed) AZ31B and as-received AZ31B. The results indicated that after 4 passes, SiO2 and graphite particles properly dispersed in the microstructure and grain growth was restricted due to the pinning effect of these particles; therefore, the mean grain size of the composite decreased by 80% compared with as-received AZ31B. The microhardness of the composite increased about 18% compared with as-received AZ31B and microhardness variation decreased in the stir zone, which indicates more homogeneity in grain size and particle distribution by increasing FSP passes. Furthermore, the investigation of strengthening mechanisms showed that grain size decrease, due to recrystallization and pinning effect of particles, had more influence on increasing composite hardness than dispersion hardening. The wear resistance of the composite which underwent 4 passes was 33% more than as-received AZ31B. It also had the highest corrosion resistance due to more stability of the passive film as a result of fine grain size.

Synthesis of a novel hybrid nanocomposite of AZ31Mg-Graphene-MWCNT by multi-pass friction stir processing and evaluation of mechanical properties

The present work is a focused study of the influence of hybridizing nano-graphene and MWCNT particulates on the microstructural and the mechanical behaviour of AZ31Mg–MWCNT-graphene hybrid composite was investigated by experimentation and its analysis. A novel hybrid nanocomposite was synthesized of AZ31Mg as base material reinforced with MWCNT and graphene nano particulates using multi-pass friction stir processing (FSP) technique. AZ31Mg plates of 6 mm thickness were drilled up to 4 mm depth with 2 mm diameter and compacted with hybrid carbonaceous reinforcements in a ratio 7:1. Multiple FSP passes were used to develop composites of AZ31Mg-MWCNT, AZ31Mg-graphene, hybrid nanocomposite AZ31Mg-MWCNT-graphene and FSPed monolithic AZ31Mg sample plates for appropriate comparison of results. The processing parameters were kept constant throughout the process for all the specimens. Microstructural characterization revealed grain refinement credited due to the uniform distribution of graphene nano-particles embedded with MWCNT. Scanning electron microscopy of AZ31Mg-MWCNT-graphene nano-hybrid composite confirmed more localized recrystallized grains and lesser tensile twin fraction, as compared to the other composites under comparison. Mechanical properties assessment specified the dominance of strength and ductility combination in the specimen of AZ31Mg-MWCNT-graphene nano-hybrid composite as compared to other composites specimens. The superior mechanical properties of the developed nano-hybrid composite attributed due to the uniform dispersion of hybridized carbonaceous nano-reinforcements and improved interfacial bonds linking the matrix and the reinforcement particles. The improvement in microhardness of the developed nano-hybrid composite is recorded as 90.6 Hv, which is much superior to other composites. The enhancements of yield strength are recorded as 32.31% and of ultimate tensile strength as 49.23%. In case of compressive strength testing, recorded improvement in 2% yield compressive strength is 50% and in case of ultimate compressive strength, it is 73.13%, whereas improvement in compressive fracture strength is noted as 8.21%, as compared to the unreinforced FSPed.

Tribological behavior of AZ31/ZrO2 surface nanocomposites developed by friction stir processing

Abstract The present study focused on the poor wear resistance of the AZ31 magnesium alloy and improving its tribological applications. Surface nanocomposites reinforced with nano-sized ZrO2 particles on the AZ31 magnesium alloy substrate were fabricated by friction stir processing (FSP) in two different pass number. The average grain size of the as-received AZ31 base metal reduced from 11 μm to 2 μm in the case of AZ31/ZrO2 surface nanocomposite developed by four passes of FSP. Secondary electron microscopy (SEM) images of the 4-pass FSPed nanocomposite showed that the ZrO2 nanoparticles distributed homogenously in the magnesium matrix. Microhardness measurements revealed a significant improvement by adding ZrO2 nanoparticles and also increasing in FSP pass number. The microhardness of the AZ31 base metal improved about 90% in the case of four passes FSPed AZ31/ZrO2 surface nanocomposite. The wear performance of the samples was evaluated using a reciprocal wear machine and AISI 52100 steel with the hardness of 63 HRC as the counterpart. Investigating the wear performance and friction coefficient of the samples revealed enhanced tribological behavior in FSPed samples. The wear rate of the AZ31 base metal reduced about 40% for the 4-pass FSPed AZ31/ZrO2 nanocomposite. The average friction coefficient of the 4-pass FSPed nanocomposites was about half of the base metal. The SEM observations of the worn surface, wear track cross-section, counterpart tip and wear debris indicated that the wear mechanism changed from severe abrasion and adhesion for AZ31 base metal to mild abrasion for the 4-pass FSPed AZ31/ZrO2 nanocomposite.

Preparation of Biodegradable Mg/β-TCP Biofunctional Gradient Materials by Friction Stir Processing and Pulse Reverse Current Electrodeposition

Mg alloys, as a new generation of biodegradable bone implant materials, are facing two tremendous challenges of enhancing strength and reducing degradation rate in physiological environment to meet clinical needs. In this study, tricalcium phosphate (β-TCP) particles were dispersed in Mg–2Zn–0.46Y–0.5Nd alloy by friction stir processing (FSP) to produce Mg-based functional gradient materials (Mg/β-TCP FGM). On the surface of Mg/β-TCP FGM, the hydroxyapatite (HA) coating was prepared by electrodeposition. The effects of FSP and electrochemical parameter on the microstructure, microhardness, bonding strength and corrosion performance of the Mg/β-TCP FGM were investigated. After four passes of FSP, a uniform and fine-grained structure was formed in Mg/β-TCP and the microhardness increased from 47.9 to 76.3 HV. Compared to the samples without β-TCP, the bonding strength of the Mg/β-TCP FGM increased from 23.1 ± 0.462 to 26.3 ± 0.526 MPa and the addition of degradable β-TCP contributed to the in situ growth of HA coating. The thickness of HA coating could be dominated by controlling the parameters of electrodeposition. According to the results of immersion tests and electrochemical tests in simulated body fluid, it indicated that the degradation rate of the Mg/β-TCP FGM could be adjusted.

Fabrication of Aluminum Matrix Composites for Automotive Industry Via Multipass Friction Stir Processing Technique

In automotive industry, materials having excellent resistance to corrosion, good wear resistance and high strength to weight ratios are important. In accordance with the required properties; aluminum, nickel, titanium, magnesium and their alloys are mostly used in this industry. Automotive components such as engine cylinders, pistons, disc and drum brakes, engine connecting rods and Cardan shafts were all made of Aluminum Matrix Composites (AMCs). In this paper, AMCs were fabricated via multi pass Friction Stir Processing (FSP) with the aim to improve its mechanical properties and corrosion performance. 7075 Al alloy was selected as matrix and Ti-6A1-4V as the reinforcing particle.

Enhancement of the microstructure homogeneity and mechanical performance of the As-Cast Mg/Mg2Si in-situ composite through friction stir processing

Multipass friction stir processing (FSP) with 100% overlap was applied to in situ Mg/Mg2Si composite in an effort to modify its as-cast microstructure. The results indicated that FSP eliminates porosities, breaks up the massive high aspect ratio Mg2Si particles and refines and homogenizes the microstructure. Uniform microhardness was observed in the FSP stir zone of the composite which was not the case for the as-cast material. As compared to the as-cast specimen, the results of the tensile test revealed the simultaneous increase in ductility by 4.5 times and in strength by 2 times by performing one pass of FSP. Investigating the fracture surface of FSP samples showed a high density of cracked primary Mg2Si particles which shows that load transfer to reinforcing particles has occurred due to the high strength of their interface.

Effect of Friction Stir Processing on the Microhardness, Wear and Corrosion Behavior of Al6061 and Al6061/SiO2 Nanocomposites

An effect of the friction stir processing (FSP), its pass numbers and addition of the SiO2 nanoparticles on microhardness, wear behavior and corrosion performance of the Al6061 aluminum alloy was investigated. Scanning electron microscopy (SEM) and optical microscopy were utilized to characterize the microstructure of the alloy, FSPed and composite samples. SEM observations revealed that the SiO2 particles were not uniformly dispersed in the matrix after two passes of FSP. However, increasing the pass number more than two passes resulted in a great improvement in the distribution of the SiO2 particles. The application of FSP led to overall softening compared to the base metal. Softening of the Al6061 alloy was probably attributed to the coarsening of Mg2Si. Corrosion resistance of the FSPed samples found a significant reduction compared to the base metal. Applying higher pass number of the process and also addition of the SiO2 nanoparticles improved the wear behavior of the samples.

Microstructure, mechanical properties and corrosion resistance of Al6061/BN surface composite prepared by friction stir processing

In this research, the effect of boron nitride (BN) reinforcement particles on microstructure and mechanical properties of Al6061-T6 surface layer composites prepared by friction stir processing (FSP) were investigated. Microstructural changes of surface composites were examined by optical microscope (OM). Also, scanning electron microscope (SEM) was utilized to evaluate dispersion of reinforcement particles. The results illustrated that the BN reinforcement particles were uniformly dispersed in the nugget zone after 4 passes of FSP. It was also determined that the micro-hardness was enhanced from 97 Hv to 157 Hv due to the pining effect of hard BN reinforcement particles and reducing the grain size of processed zone from 312.65 μm to 12.09 μm. The results also indicated that increasing the number of FSP passes increased hardness, as well as the yield strength (σy), tensile strength (σUTS) and elongation (%E) of specimens. Corrosion resistance of Al6061/BN surface composite was examined by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Results showed that Al6061/BN surface composite presented better corrosion behavior in comparison to Al6061-T6 and FSPed Al6061-T6 without BN reinforcement particles.

Effect of Multi Pass Friction Stir Processing on Surface Modification and Properties of Aluminum Alloy 6061

In the present investigation, friction stir processing (FSP) is carried out with multi pass processing having 100 % overlap zone on the workpiece material of aluminum alloy 6061 with constant FSP parameters and varying multi pass processing conditions. Novel processing concept of multi pass FSP was performed with different rotation directions (such as clock wise and anti-clock wise directions) and processing directions (such as forward, reverse and revert directions). Surface inspection, macrographs and microstructures of the processed regions are evaluated and compared with each other. Multi-pass FSP with 100 % overlapping of two passes caused intense dynamic recrystallization and resulted in reduced grain size. Hardness of processed zone was found increased in case of two pass FSP. Minimum tensile strength was reported with double sided FSP compare to single pass and two pass FSPs. No major variations in tensile strength were reported in case of single pass and two pass FSPs.

Through-thickness inhomogeneity in microstructure and tensile properties and tribological performance of friction stir processed AA1050-Al2O3 nanocomposite

Friction stir processing (FSP) is used to fabricate Al-Al2O3 nanocomposite by addition of Al2O3 nanoparticles into a groove in AA1050 aluminum alloy and being processed using FSP. Evolution of grain structure, distribution of the Al2O3 nanoparticles, tensile properties and tribology are investigated in four samples extracted from each 2 mm of the fabricated composite, respectively from top surface. It was found that the finest grain structure formed in the second region from the top surface due to the most efficient stirring in this region. In addition, the presence of nanoparticles with an efficient distribution in this region may inhibit grain growth and lead to an eventually fine grain structure. After one pass of FSP, nanoparticles were found to be efficiently distributed in the top surface and less uniformly distributed in other regions leading to formation of particle depleted regions (PDRs) and coarse agglomerated particles. Fracture in the tensile test samples changed from ductile to brittle in the sample with agglomerated particles. Application of the second cycle of FSP leaded to further grain refinement, more uniform distribution of nanoparticles and less agglomerated coarse particles and consequently leaded to more uniformity in tensile properties and tribology behavior of the samples. This was the most effective on grain refinement for the regions which were not efficiently refined or with more extended PDRs in the first cycle. Coefficient of friction (CoF) of aluminum was significantly reduced with addition of Al2O3 particles which was attributed to increase in strength and reduction in sliding contact area.

Evaluating the microstructure and mechanical properties of friction stir processed Al–Si alloy

ABSTRACTIn this study, mechanical behaviour and microstructural evolution in friction stir processing (FSP) of casting hypereutectic A390 aluminium alloy have been investigated. The mechanical behaviour of FSP samples was investigated by measuring the strain rate sensitivity using shear punch testing. The room-temperature shear punch tests were conducted at shear strain rates in the range of 10−4–10−1 s−1. The results indicate that the strain rate sensitivity index increases from about 0.015 to 0.120 for as-cast A390 after third FSP pass and then experiences a further growth in FSP passes. The increase in the grain size and CuAl2 intermetallic particle size result in a reduction in strain sensitivity index as well as shear strength after third FSP pass.

Fabrication and Characterization of A5083-WC-Al2O3 Surface Composite by Friction Stir Processing

In this study, WC-Al2O3 ceramic composite was incorporated into Al5083 to produce a surface composite by friction stir processing (FSP), and the microstructure, hardness and wear properties of Al5083-WC-Al2O3 surface composite were evaluated. Optical microscopy of FSPed samples showed grain refinement in the stir zone. The addition of WC-Al2O3 particles as well as increase in FSP pass number had a considerable effect on grain refinement, and the grain size of Al5083 base metal of 36 µm reduced to 11 µm for Al5083-WC-Al2O3 surface composite after four passes. The SEM observation of the surface composite revealed that the WC-Al2O3 particles distributed homogenously in the matrix and by increasing the FSP passes, the initial agglomerates of mechanochemically synthesized WC-Al2O3 powders could be fractured. Microhardness evaluation showed a substantial improvement by adding WC-Al2O3 particles and increase in FSP pass number. The maximum microhardness value of 101 HV belonged to surface composite after four passes, while the microhardness of the base metal was 65 HV. Wear test results revealed enhanced tribological behavior with a similar trend of microhardness values. Scanning electron microscopy tests revealed both adhesive and abrasive wear mechanisms on the surface of the wear test specimens.

Surface composite on Cu substrate with SiO2 reinforcement fabricated by severe plastic deformation: Microstructure, mechanical and tribological properties

In this study, the mechanical and tribological properties of copper/SiO2 composites fabricated by the friction stir processing (FSP) were investigated. Micro-hardness measurements and tensile testing as well as atomic force and scanning electron microscopy were utilized to characterize the fabricated composites. The results showed that increase in the number of FSP passes leads to significant improvement in the mechanical properties. The microhardness and tensile strength of the sample fabricated by four passes of FSP improve by about 149% and 70% with respect to the base metal, respectively. In contrast, ductility dramatically degrades as more FSP pass are applied. The investigations into the wear behavior of fabricated samples showed that the weight loss and friction coefficient remarkably decrease in the composites. It was also observed that the wear rate in the fabricated samples decrease with increase in the number of FSP passes.