Multi-pass Friction Stir Processing Research Articles

Development of AA5052/TiO2/SiC hybrid surface composites using upward material flow through multipass friction stir processing

The present study employed upward material flow during friction stir processing (FSP) to develop AA5052/TiO2/SiC hybrid surface composites rather than the downward material flow that is conventionally used. The upward material flow was generated with the help of a right-handed threaded pin tool rotating in a clockwise direction causing plastically deformed material to flow in the three-dimensional region of the stir zone. The result showed that the upward material flow pattern and multipass significantly improved the properties of composites. Substantial grain refinement was obtained after each successive pass due to the uniform distribution of fragmented reinforcement particles and intense plastic deformation during FSP. The maximum microhardness of 88.73 HV and ultimate tensile strength of 220.8 MPa were obtained after the fourth FSP pass in developed hybrid surface composites. Additionally, the tribological analysis showed that wear resistance increased with the number of passes.

Effects of multi-pass friction stir processing on mechanical and tribological properties of Mg–Zn–Zr alloys

Owing to high strength and good biocompatibility, Mg–Zn binary alloys have attracted significant attention as a potential candidate for producing human implants. However due to the formation casting defects and dendritic structure, these alloys show poor mechanical and wear performances. Alloying and applying severe plastic deformation methods are suggested as two techniques for modifying and improving the above properties. In this study, dry-sliding wear and friction behaviors of the Mg–0.5Zn (MZ) alloy were enhanced by micro-alloying with Zr (0.25 wt%) and applying multi-pass friction stir processing (FSP) technique. Adding Zr reduced the average grain size (AGS) from 1.5 ± 0.3 mm in the MZ sample to about 510 ± 50 μm through the formation of evenly distributed Zr-rich particles with the chemical composition of Mg: 8.84, Zn: 0.75, and Zr: 90.41 A% in the structure. Furthermore, the attendance of thermostable Zr particles stimulated the dynamic recrystallization (DRX) during FSP and reduced the AGS to less than ≈2 μm after the 3rd FSP pass. This substantial grain refinement along with the casting defects reduction, and the fragmentation and redistribution of Zr particles enhanced the hardness and tensile properties of the substrate. Thus, the improved substrate in the FSPed samples, increased the stability of the formed tribolayer on the worn surfaces and changed the wear mechanisms from severe adhesive/delamination in the MZ alloy to mild abrasive/adhesive in the FSPed Zr-modified samples. Therefore, in the optimal condition (3-pass FSPed Mg–0.5Zn–0.25Zr sample), the hardness and total elongation percentage (EL%) increased by 55% and 648% while the mass loss and average friction coefficient (AFC) were reduced by 54% and 39%, respectively, compared to the as-cast Mg–0.5Zn alloy (under a load of 30 N).

Effect of different volume ratios of SiC and TiO2 reinforcement particles on mono and hybrid surface composites of AA7075-T651 through friction stir processing

In the present work, the different volume ratios of silicon carbide and titanium dioxide particles were incorporated with AA7075-T651 to improve the surface properties using multipass friction stir processing. The metallurgical study of the friction stir processed samples was examined through optical microscopy and field emission scanning electron microscopy with energy-dispersive X-ray analysis. In addition, the microhardness, wear, and corrosion properties were measured and analyzed. The results revealed that the increased amount of SiC particles caused uniform particle dispersion and was devoid of cluster-rich regions within the matrix. The increased volume of SiC particles exhibited a smaller grain size due to higher grain refinement. The sample with 100% SiC showed superior mechanical, tribological, and corrosion properties. The microhardness of sample with 100% SiC was increased by 13.60% compared to base metal, it was also better compared to other composite samples. Similarly, the coefficient of friction, wear rate, and corrosion resistance properties were reduced by 43.24%, 14.98%, and 75%, respectively.

Microstructural, mechanical and tribological performance of a magnesium alloy AZ31B/Si3N4/eggshell surface composite produced by solid-state multi-pass friction stir processing

This study focused on the development of an AZ31B/Si3N4/Eggshell surface composite via solid-state multi-pass friction stir processing. The study aimed to characterize the developed surface composite based on its structural, microstructural, mechanical, and tribological performance at one, two and three successive tool-passes. The structural and compound analysis was conducted using an XRD pattern. Microstructural characterization and grain refinement studies were conducted using FESEM images and EBSD analysis. Furthermore, the mechanical properties were investigated through tensile tests equipped with digital image correlation (DIC) images and fractography analysis via FESEM images. In addition, tribological characteristics, such as COF, friction forces, and volumetric wear losses, were examined using a universal tribometer, and the 3D profile of the wear track was analyzed through surface profilometry. The results revealed the formation of structural compounds such as Mg2Al4, Mg2SiO4, Mg2Ca, and Ca2Mg4Zn13 in the stir zone. The morphological study revealed plenty of white-grey (ESP) and dark grey (Si3N4) sub-micron precipitates uniformly dispersed into the AZ31B matrix alloy. The EBSD map exhibited an average grain size of 2.95 ± 1.83 μm. The ultimate tensile stress at one, two and three successive tool-passes were found to be 357 MPa, 366.5 MPa and 375.4 MPa, respectively, which was comparatively 20–25% higher than the base alloy. The FESEM images of the fractured surface exhibited ductile striations and tear ridges with flat shear bands mixed with brittle fracture. The lowest COF obtained in this study was 0.29 for three too-passes at an average frictional force (Fx) of 2.17 N with a volumetric wear loss of 0.0769 mm3.

Effect of Multipass Friction Stir Processing on Structure and Mechanical Properties of CuAl9Mn2 Copper Alloy

This study examines the structure and mechanical properties of CuAl9Mn2 copper alloy processed via friction stir processing. Workpieces, 2 mm thick, were processed using four tool passes. After the initial FSP pass, the stir zone structure was found to be non-homogeneous, with grains changing from equiaxed to elongated in the material flow direction. Grain sizes decreased from 80-140 µm to 3-8 µm. However, after the fourth pass, the stir zone became more homogeneous with equiaxed grains and sizes ranging from 2-6 µm.
 The increase in microhardness and tensile properties of the material is attributed to the processing temperature, mechanical mixing, and grain refinement. The ultimate tensile strength of the FSP material increased by 13% relative to the metal prior to processing, whether one or four passes were used. Additionally, microhardness in the stir zone increased, which is consistent with the results of mechanical tensile tests.

Interfacial microstructure and strengthening mechanisms of SPSed Al/GNP nanocomposite subjected to multi-pass friction stir processing

Interfacial microstructure and strengthening mechanisms of SPSed Al/GNP nanocomposite subjected to multi-pass friction stir processing

Effect of multi-pass friction stir processing on mechanical, microstructural, bioactivity, and corrosion properties of novel magnesium-hopeite composite for biomedical applications

The mechanical properties of magnesium and its alloys are remarkably close to those of natural bone, and they are biodegradable, thus they have been studied for use in consumable bio-implant applications. However, their applicability is constrained by the unpredictable corrosion rate and the moderate bioactivity of Mg-based materials in a biological environment. Considering this, a Hopeite-reinforced magnesium composite was fabricated using friction stir processing (FSP). Along with the many other advantages of FSP, it significantly reduces grain size. The impact of reduced grain size and the presence of Hopeite particles on the control of magnesium degradation was studied. After FSP, there was a significant reduction in grain size owing to severe plastic deformation and dynamic recyclization. The effect of the number of passes was studied using samples with one pass, two passes, and three passes of Mg-Hopeite composite. There was a correlation between increasing the number of FSP passes and improvements in the material's mechanical characteristics, corrosion resistance, and bioactivity behavior. The samples were immersed in simulated body fluid for in vitro bioactivity studies, where it was determined that the 3 passes FSP Mg-Hopeite composite had the greatest Ca/P ratio and hence the best bioactivity, outperforming the 2 passes composite, the 1 pass composite, and pure Mg. Apatite layer formation in FSP Mg-Hopeite composite samples has also conformed to their bioactive behavior. Electrochemical and immersion studies designed to evaluate the corrosion behavior of the material in simulated bodily fluid revealed that grain refinement and an increase in biomineralization led to an improvement in the material's corrosion resistance. Considering the findings, which indicate that 3 passes of FSP Mg-Hopeite composite possess superior corrosion resistance, and bioactive and mechanical properties in comparison to either 1 pass and 2 passes of FSP Mg-Hopeite composite or pure Mg, this material is ideally suited for use as temporary implants for biomedical applications.

Multipass Friction Stir Processing of Laser-Powder Bed Fusion AlSi10Mg: Microstructure and Mechanical Properties.

The effect of multipass friction stir processing (FSP) on the microstructure and mechanical properties of an AlSi10Mg alloy produced by laser-powder bed fusion was investigated. FSP was performed at a rotational speed of 950 rpm and traverse speed of 85 mm/min. The results indicated that FSP destroyed the coarse grain structure in the as-built AlSi10Mg by generating fine and equiaxed grain structures with shear texture components of A1*(111)[1¯1¯2] and A2*(111)[112¯], in addition to causing fragmentation and refinement of the Si networks. FSP reduced the tensile strength slightly but significantly improved ductility. One-pass FSP exhibited superior mechanical properties compared with the two- and three-pass scenarios. The higher strength of the one-pass sample was attributed to the strengthening mechanisms induced by the Si particles, which were grown by repeated FSP. The higher ductility of the one-pass sample was explained using the kernel and grain average misorientations. Furthermore, the post-FSP microstructural evolution and fracture behavior of the samples were discussed.

Macro- and Microstructure of In Situ Composites Prepared by Friction Stir Processing of AA5056 Admixed with Copper Powders.

This paper is devoted to using multi-pass friction stir processing (FSP) for admixing 1.5 to 30 vol.% copper powders into an AA5056 matrix for the in situ fabrication of a composite alloy reinforced by Al-Cu intermetallic compounds (IMC). Macrostructurally inhomogeneous stir zones have been obtained after the first FSP passes, the homogeneity of which was improved with the following FSP passes. As a result of stirring the plasticized AA5056, the initial copper particle agglomerates were compacted into large copper particles, which were then simultaneously saturated by aluminum. Microstructural investigations showed that various phases such as α-Al(Cu), α-Cu(Al) solid solutions, Cu3Al and CuAl IMCs, as well as both S and S'-Al2CuMg precipitates have been detected in the AA5056/Cu stir zone, depending upon the concentration of copper and the number of FSP passes. The number of IMCs increased with the number of FSP passes, enhancing microhardness by 50-55%. The effect of multipass FSP on tensile strength, yield stress and strain-to-fracture was analyzed.

Effect of Friction Stir Processing on the Fatigue Performance of AZ31 Magnesium Alloy

Herein, the cyclic mechanical behavior of AZ31 magnesium alloy after multipass friction stir processing (FSP) is investigated up to the very high‐cycle fatigue (VHCF) regime. The grain refinement and texture evolution after processing are evaluated to enhance the understanding of the fatigue response. Although ultimate tensile strength and ductility of the friction stir processed AZ31 increase up to about 320 MPa and 25%, respectively, the fatigue performance deteriorates in comparison with that of the as‐received condition due to the low yield strength and texture evolution after processing. Furthermore, analysis of fracture surfaces of the samples after cyclic loading reveals that the as‐received AZ31 is more prone to brittle fracture with multiple‐origin fatigue failure even at low stress amplitudes. On the contrary, the dominant failure mechanisms of the friction stir processed samples are initiation and propagation of cracks originating from the surface, porosities, and grain size inhomogeneity. Nevertheless, the capability of FSP for providing superior crack initiation resistance in the VHCF regime is demonstrated as a significant contribution. Based on a detailed study of prevalent microstructural features, processing–property–damage relationships are established indicating the major effect of FSP on the final performance of the AZ31 magnesium alloy.

Grain Structure Formation and Texture Modification through Multi-Pass Friction Stir Processing in AlSi10Mg Alloy Produced by Laser Powder Bed Fusion.

A new strategy is proposed to modify the grain structure and crystallographic texture of laser-powder bed fusion AlSi10Mg alloy using multi-pass friction stir processing (FSP). Accordingly, 1-3 passes of FSP with 100% overlap were performed. Scanning electron microscopy and electron backscattered diffraction were used for microstructural characterization. Continuous dynamic recrystallization and geometric dynamic recrystallization are the governing mechanisms of grain refinement during FSP. The stir zones have bimodal grain structures containing large and fine grains. The multi-pass FSP caused a considerable increase in the volume fraction of the large-grained area in the stir zone, which contained higher values of low-angle boundaries and sharp shear texture components of B(11¯2)[110] and B¯(1¯12¯)[1¯1¯0]. The formation of low-energy grain boundaries in the stir zone and alignment of the low-energy crystallographic planes with the surface of the sample made the strategy of using multi-pass FSP a promising candidate for corrosion resistance enhancement in future studies. Moreover, the detailed evolution of the grains, texture components, grain boundaries, and Si particles is discussed.

In-Situ Al-Mg Alloy Base Composite Reinforced by Oxides and Intermetallic Compounds Resulted from Decomposition of ZrW2O8 during Multipass Friction Stir Processing.

In the presented work, the effect of friction stir processing admixing the zirconium tungstate ZrW2O8 powder on the microstructure, mechanical and tribological properties of the AA5056 Al-Mg alloy stir zone has been studied. The FSP resulted in obtaining dense composite stir zones where α-ZrW2O8 underwent the following changes: (i) high-temperature transformation into metastable β'-ZrW2O8 and (ii) decomposition into WO3 and ZrO2 oxides followed by the formation of intermetallic compounds WAl12 and ZrAl3. These precipitates served as reinforcing phases to improve mechanical and tribological characteristics of the obtained fine-grained composites. The reduced values of wear rate and friction coefficient are due to the combined action the Hall-Petch mechanism and reinforcement by the decomposition products, including Al2O3, ZrO2, β'-ZrW2O8 and intermetallic compounds such as WAl12 and ZrAl3. Potential applications of the above-discussed composites maybe related to their improved tribological characteristics, for example in aerospace and vehicle-building industries.

Investigation of initial metallurgical factors on the dynamic impact response and adiabatic shear bands formation of the 6061 Al alloy

The effect of multi-pass friction stir processing and initial base metal condition on the dynamic impact response of AA6061-T6 alloy at high strain rates was investigated in this study. The Split-Hopkinson Pressure Bar (SHPB) was used in dynamic experiments with strain rates ranging from 1600 to 4200/s. The results revealed that the base metal alloy's (BM) dynamic flow stress was comparable to all the friction stir processed AA6061-T6 (FSP'd) specimens as the strain rate and true strain increased. The general increase in stress response levels as strain rates and true strain increases can be attributed to strain hardening. The higher values of strain rate sensitivity in multi-pass FSP'd specimens are an indication that they are more ductile in comparison to the BM condition. The optical and electron backscattered diffraction (EBSD) analysis showed that adiabatic shear bands were formed by heterogeneous deformation. The EBSD analysis revealed that the FSP'd specimens showed more abnormal grain growth and dynamic recrystallized sites than BM. The substantial decrease in dynamic flow stress, and high strain rate sensitive values of multi-pass FSP'd specimens compared to BM for all the investigated strain rates attributed to softening effect by dynamic recrystallization (DRX), and the emergence of abnormal grain growth during friction stir process.

Effect of nanoparticles and multipass friction stir processing on microstructure and mechanical properties of AA7475

The base metal, AA7475, initially contained nanoparticles of SiC within a coarse dendritic structure. The multipass FSP (MPFSP) process successfully broke these coarse and dendritic clusters, resulting in a homogenous microstructure in the stir zone. This inhibition led to a continual reduction in grain size. The presence of SiC reinforcement particles also played a role in imbvproving the microstructure and tensile properties of the MPFSP/SiC composite. The optimal process parameters for MPFSP/SiC on AA7475 were identified as a rotational tool speed of 1500 rpm, welding speed of 40 mm/min, and a tilt angle of 2°. As the number of FSP passes increased, the agglomeration of SiC particles reduced, further enhancing the dispersion. Before MPFSP/SiC, the base metal AA7475 exhibited a tensile strength of 410±5 MPa and a % strain of 10.83±0.3. However, after MPFSP/SiC, the tensile strength increased with the number of FSP passes. The highest tensile strength of 521±8 MPa was observed after the 5 th pass of FSP. This increase in tensile strength was attributed to the presence of fine grains formed through the DRX mechanism during the MPFSP process.

Effect of Multi-Pass Friction Stir Processing on Microstructure and Mechanical Properties of a Metastable Dual-Phase High Entropy Alloy

Studies on Multi-pass Friction Stir Processing (FSP) of Fe49.5Mn30Co10Cr10C0.5, a metastable dual-phase High Entropy Alloy (HEA), were carried out with the aim to systematically investigate the microstructural changes occurring during different passes, and to evaluate the mechanical response of this alloy with progressive passes. A reduction in grain size and a change in HCP volume fraction was observed after each pass. Dynamic recrystallization, occurring during FSP, led to grain refinement, and the transformation induced plasticity (TRIP) effect resulted in observed changes in HCP phase fraction. One-pass FSPed material exhibits a higher work hardening rate and a higher ultimate tensile strength (UTS.) value, as compared to both, an annealed and two-pass FSPed material. This is due to a combination of two factors, a small grain size and a large fraction of metastable Face Centred Cubic (FCC) phase, in the microstructure of the one-pass material.

The effect of multi-pass friction stir processing on microstructure, mechanical properties, and corrosion behavior of WE43-nHA bio-composite

The influence of multiple passes during friction stir processing (FSP) on the evolution of microstructure, hardness, compressive strength, and corrosion behavior of a Mg-based bio-composite has been investigated. WE43 Mg alloy was used as the matrix of the composite and nano-sized hydroxyapatite (nHA) was added as the second material to form the composite. After fabrication of the composite by one pass of FSP, the process was repeated six times. Significant grain refinement and fragmentation of secondary phase particles were observed during FSP. Increasing the number of passes of FSP was found to be associated with pronounced grain refinement coupled with the uniformity in distribution of nHAs. Corrosion resistance is enhanced with an increasing number of FSP passes, which is attributed to the fragmentation and redistribution of secondary phase particles in addition to a homogeneous distribution of nHA.

Enhancement of tensile and fatigue properties of hybrid aluminium matrix composite via multipass friction stir processing

In present work, friction stir processing (FSP) has been used to fabricate hybrid aluminium matrix composite (HAMC) using a mixture of 6% ZrO2 and 6% Ni as reinforcement particles. Four different passes (1, 2, 4, and 6) were used to study the influence of multipass FSP on tensile properties, residual stresses, and fatigue performance of HAMCs. Six pass FSP led to significantly improved tensile properties due to more uniform distribution of reinforced particles and refined grains, and enhanced compressive residual stresses to −106 ± 6.8 MPa compared to −9 ± 1.8 MPa in base material. The increment in fatigue life of HAMCs is 31% (two passes), 61% (four passes), and 69% (six passes) as compared to the base material (4.08 × 105 cycles) for the lowest maximum applied stress of 100 MPa. The fatigue fracture characteristics of HAMCs with more than one FSP pass were found to be ductile-brittle mixed mode. The study concluded better fatigue life of HAMC obtained using six passes.

Enhancement of mechanical properties and wear of AA5083/316 stainless steel surface-composite developed through multi-pass friction stir processing (MPFSP)

Enhancement of mechanical properties and wear of AA5083/316 stainless steel surface-composite developed through multi-pass friction stir processing (MPFSP)

A new insight into LPSO phase transformation and mechanical properties uniformity of large-scale Mg-Gd-Y-Zn-Zr alloy prepared by multi-pass friction stir processing

A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing (MFSP) technology in this work. The structure of grains and long period stacking ordered (LPSO) phase were characterized, and the mechanical properties uniformity was investigated. Moreover, a quantitative relationship between the microstructure and tensile yield strength was established. The results showed that the grains in the processed zone (PZ) and interfacial zone (IZ) were refined from 50 µm to 3 µm and 4 µm, respectively, and numerous original LPSO phases were broken. In IZ, some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms. The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly, greatly increasing the transformation rate of LPSO phase. After MFSP, the ultimate tensile strength, yield strength and elongation to failure of the large-scale plate were 367 MPa, 305 MPa and 18.0% respectively. Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample. In particularly, the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ. This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.

The effect of multi-pass friction stir processing on microstructure and mechanical properties of dual-phase brass alloy

This research aims to improve the microstructure and mechanical properties of C38000 brass alloy by multi-pass friction stir processing (MPFSP). In this study, The MPFSP was carried out on a dual-phase brass alloy sheet with a thickness of 5 mm at fully annealed conditions. To determine the effect of the number of passes on microstructure and mechanical properties of this alloy, rotational and traverse speeds were chosen at 750 rpm and 100 mm∖min, respectively. This process was performed in 1, 2, 4, and 6 passes. Metallography, microhardness, tensile, wear, and fractography are tests done to investigate the changes in microstructure and mechanical properties after processing. Finally, the relation between the microstructural and mechanical properties of MPFSPed specimens was discussed. Studying the tests mentioned above resulted that the MPFSP has caused a decrease in the grain size of the matrix and second phase (β′) particles. Furthermore, mechanical properties such as yield strength, ultimate tensile strength, and hardness were enhanced. It was obtained that elongation to failure has a decreasing trend with increasing the number of FSP passes. Tribological behaviors were also improved after performing MPFSP. The levels of grain size refining and improving the mechanical properties are directly related to increasing the number of passes. However, after performing six passes of FSP, there was no significant change in the microstructure and mechanical properties in comparison to that after 4 passes of FSP. The properties of 4 and 6 passes FSPed specimens showed that these had the most refined microstructures and enhanced mechanical properties with remarkable elongation.