Friction Stir Processing Passes Research Articles

Microstructural, mechanical and wear behaviour of AA7075/ZrSiO4 surface composite developed via multi pass friction stir processing

ABSTRACT The microstructural, mechanical, and wear behaviour of the ZrSiO4-reinforced AA7075 surface composites fabricated through friction stir processing was analysed. The microstructure of the friction stir processed surface composite shows refined grain 52 μm, 20 μm and 5 μm after 1, 2 and 3 FSP pass which also leads to the uniform dispersion of reinforced ZrSiO4 particles in the A7075 surface as revealed by SEM, EDS, and XRD. The microhardness and tensile strength of the FSP surface composite were significantly improved by 35% and 54%, respectively, with the effect of ZrSiO4 particles, after six passes as compared to the substrate material. The slurry abrasive wear resistance of the surface composite after six FSP passes increased to 95% as compared to the A7075 substrate material. Similarly, the slurry erosive wear resistance was improved with increasing slurry rotating speed, but as slurry concentration increased at six passes, the wear rate decreased further due to self-colloids occurring between the slurry particles. Hence, slurry erosive wear resistance was increased by up to 220% as compared to substrate material. Hence, the novel fabrication of friction stir processed surface composite will be very beneficial for aerospace and marine structural components and the fabrication process is very robust and cost-efficient.

Evaluation the effect of multi-pass friction stir processing on the wear, mechanical properties, and microstructure of the AA1050/ZrO2 surface nanocomposite

This work presents surface nanocomposites of aluminum alloy AA1050, reinforced with zirconium oxide (ZrO2) nanoparticles developed through multipass friction stir processing (FSP). This article attempts to study the effects of the number of passes on the wear rate, microhardness profile, tensile properties, and macrostructure of surface nanocomposites. The results demonstrate that an improved distribution of ZrO2 nanoparticles is obtained following each FSP pass, and that the number of passes increases with a decrease in stir zone (SZ) grain size. Consequently, it was found that applying FSP passes continuously enhances the materials' microhardness and tensile characteristics. In the microstructure development of the stir zone during the ZrO2 nanoparticle FSP, dynamic recrystallization (DRX) was an essential mechanism. The main reason for this is that surface nanocomposites with homogenous ZrO2 particle dispersion and no discernible particle clustering in the stir zone were shown by microstructural studies conducted through FSP, which significantly reduced the matrix grain size. The AA1050 base metal (BM) has an ultimate tensile strength, yield strength, and hardness of 59.2 MPa, 24 MPa, and 30.1 respectively. The nanocomposite generated by 5 FSP passes exhibits improved yield stress (55 MPa), tensile strength (94.5 MPa), and microhardness (86.5 HV), but its tensile ductility decreased from 34% to 23.8% when compared to the base metal. Tensile strength that is higher is the outcome of fine dimples' ability to pin the dislocation movement during tensile loading. According to fractographic studies, the ductile–brittle mode replaced the dimple-shaped ductile fracture mode.

Microstructure, mechanical and tribological properties of AA5083-TiO2 nanocomposite by multi-pass friction stir processing

This study examines the impact of Friction Stir Processing (FSP) with TiO2 nanoparticle incorporation on the microstructural, mechanical, and tribological properties of AA5083 Metal Matrix Composites (MMCs). It offers a detailed analysis of the alterations in the alloy’s characteristics due to FSP. Microstructural examination was conducted using optical microscopy (OM) and scanning electron microscopy (SEM). Significant findings include the microstructural refinement where TiO2 nanoparticle addition during FSP shrank the grain size from 20 to 3 µm after one pass, which then rose to 7 µm following four passes. Mechanical properties, specifically microhardness and tensile strength, were assessed. Results indicated that after four FSP passes, the material can reach a yield strength of 192 MPa and an ultimate tensile strength (UTS) of 359 MPa, alongside a consistent microhardness of 103 HV0.1. Furthermore, it was observed that increasing FSP passes enhances energy absorption, although it remains lower than that of the base material. Analysis of fracture and wear mechanisms has led to the conclusion that with more passes, fracture mechanisms transition to a mix of ductile and brittle behaviors, and the friction coefficient decreases by up to 22.95%.

Superior tribological properties of highly-loaded graphite/A356 surface composites fabricated using friction stir processing

In this work, friction stir processing (FSP) was used to prepare graphite (Gr) / A356 alloy composites with superior tribological properties. The Gr content and number of FSP passes (up to three passes) were used as processing variables. The microstructure, hardness and wear resistance of the composites were studied and compared with a neat sample. The microstructural studies demonstrated that super-fine Gr particles were uniformly distributed and in-situ sub-micron Al4C3 particles were formed after three FSP passes. Hardness measurements proved that all composites exhibited higher hardness than the neat sample. The composite prepared using two Gr loading rounds and three FSP passes achieved the highest hardness value of 331 kg.f/mm2, which is more than 4 times that of the neat sample. Additionally, the wear rate of this composite was approximately 57 % lower than that of the neat sample. The superior hardness and wear resistance of the fabricated composites are attributed to the in-situ exfoliation of graphite and the formation of super-fine Al4C3 particles during FSP.

Sn/Graphite/Cu reinforced aluminum: An experimental study on fabrication of hybrid surface composite as journal bearing material by friction stir processing

Friction stir processing (FSP) is an energy-efficient and environmentally friendly technique that provides tailored manufacturing possibilities for surface composites in solid-state conditions. This study focuses on manufacturing solid lubricant-reinforced aluminum matrix surface composite (AMSC) through FSP, which can be used as a journal-bearing material. Composite fabrications are performed utilizing Sn, Cu, and graphite particles (hybrid powder) with four passes of FSP. The cross-sectional macro and microstructures of obtained surface composites are investigated via optical microscopy (OM) and scanning electron microscopy (SEM). The stir zone (SZ) chemistry is analyzed with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The microhardness measurements show the effects of hybrid powder as reinforcement and FSP parameters on the mechanical features of the composite cross-sections. Wettability and tribological tests are also conducted to determine the surface properties of the fabricated composites. According to the findings, the wear rate is decreased by 8 % with the reduction of average CoF to 0.75, while a hardness increment is achieved over ∼35 % in manufactured surface composites compared to the base material. It is observed that the content and amount of the hybrid powder and FSP parameters employed can ensure the fabrication of desired characteristics compatible with the aim in surface composites.

Application of friction stir surface treatment for modification of peripheral coarse grain structure and mechanical properties of AZ31 Mg alloy

The presence of peripheral coarse grains (PCG) in the microstructure of extruded products is considered one of the causes of decreased mechanical properties. Such microstructure has been observed at the periphery of extruded AZ31 Mg alloy. This research aims to achieve a refined and homogeneous microstructure at the structure of extruded bars of AZ31 alloy using pinless friction stir processing (FSP). Up to six passes of FSP using pinless tools with different shoulder surface geometries were conducted. Tools with varying diameters of 12, 15, and 22 mm were used to investigate the effect of shoulder geometry. The rotational speed and traverse speed of the tool were set at 900 rpm and 70 mm/min, respectively. The tool tilt angle was also set to 3°. The effect of the tool geometry on the metallurgical and mechanical properties was investigated using metallography tests, microhardness testing, tensile testing, and fracture testing. According to the results, it was found that reducing the diameter of the tool and using featured tool can lead to homogenization and reduction of the average grain size in the processed samples, increasing the microhardness compared to the primary sample. It was also observed that mechanical properties were improved with the increase in the tool diameter due to the improved quality of the processing area. For samples processed with a 22 mm diameter tool, the final strength reached 242.7 and 248.81 MPa, respectively, for the simple and featured tools.

Investigating the Impact of Friction Stir Processing on the Hydrogen Embrittlement in AA6082-T6 Heat-Treatable Aluminum Alloy

This study investigates the impact of friction stir processing (FSP) on the hydrogen embrittlement (HE) in AA6082-T6 heat-treatable aluminum alloy. The effects of different number of FSP passes and different hydrogen cathodic charging (HCC) conditions on the material’s response to HE are examined through comprehensive mechanical testing, microhardness analysis, and microstructural characterization. The results revealed that FSP leads to a decrease in yield strength, ultimate tensile strength, and microhardness, accompanied by an increase in energy absorption. The introduction of hydrogen through HCC significantly reduces mechanical properties, particularly in non-FSPed specimens. Notably, specimens with 8 FSP passes exhibit an interesting behavior with a slight increase in energy absorption and microhardness values after HCC. Microstructural analysis shows that FSP refines the microstructure, resulting in enhanced resistance to hydrogen-induced blistering effects. These findings contribute to the understanding of hydrogen embrittlement in FSPed aluminum alloys, providing insights for developing surface-modified materials suited for hydrogen-rich applications.Graphical

Analyzing the Influence of Microstructure on the Mechanical Properties of TIG Welded Joints processed by Friction Stir considering the sampling Orientation

The contribution of the microstructural arrangement to the mechanical properties of friction stir processed Tungsten Inert Gas (TIG) welded joints is reported in this work. The TIG-welded joints were subjected to a single pass of Friction Stir Processing (FSP). The friction stir processed joint was sampled transversally and longitudinally, and different tests were conducted and studied comparatively. The microstructural analysis showed refined grains with varying degrees. The mean grain size for the transversally sampled specimen was found to be 11.48 µm, while the longitudinally sampled specimen had varying mean grain size from 7.32 µm to 15.09 µm. The varying mean grain size of the longitudinally sampled specimen is caused by the staggered arrangement of the microstructure. The tensile properties and the microhardness of the transversally sampled specimen were lower than those of the longitudinally sampled specimen. The ultimate tensile strength of the transversally sampled specimen was found to be 87.88 MPa which is lower than that of the longitudinally sampled specimen (133.83 MPa). The microhardness of the longitudinally sampled specimen fluctuated between 30 HV and 80 HV while the transversally sampled specimen had a maximum microhardness of approximately 57 HV.

Use of Multi-pass FSP treatment for improving mechanical properties and corrosion resistance of Mg-2Zn-HA composite

Magnesium (Mg) alloys are very popular among the biomaterials for biodegradable bone implants due to their suitable properties matching with that of human cortical bone. However, their poor corrosion resistance in biological fluid is a major constraint to become an ideal choice for bioimplants. The corrosion resistance of Mg-alloys is further retarded with microstructural impurities such as micro-pores, micro cracks, heterogeneous distribution of alloying element etc., which is commonly present in as-cast Mg-alloys. In present study, Friction stir processing (FSP) has been performed on Mg-2Zn alloy to refine the microstructures as well as to develop Mg-Zn-HA composites by using HA powder reinforcement. HA powder reinforcement was added using micro-grooves and multiple FSP passes on as-cast Mg-2Zn alloy having average grain size of 63.86 µm. Filling HA powder in 2-grooves and using 3-pass FSP, a refined microstructure having an average grain size of 7.15 µm and homogeneous distribution of HA powder was obtained for the developed Mg-Zn-HA composite. The Mg-Zn-HA composite developed with 3-pass FSP treatment has shown significant improvement in tensile strength and corrosion resistance as compared with as-cast Mg-alloy.

Effect of multiple passes on the properties of Al-5052/SiC surface composites fabricated via friction stir processing

Friction stir processing (FSP) has emerged as a promising technique for producing surface composites with enhanced mechanical, microstructural and tribological properties. This work investigates the influence of multi-pass FSP on various properties of aluminium 5052 alloy reinforced with silicon carbide (Al-5052/SiC). The results indicated that multi-pass FSP effectively dispersed SiC particles within the aluminium matrix, resulting in a refined microstructure and improved mechanical properties. As the number of FSP passes increased, hardness, tensile strength, and wear resistance improved, reaching levels significantly higher than the base Al-5052 alloy. Tensile strength, yield strength, and average microhardness in the five-pass FSPed specimen were improved by about 25 %, 26 %, and 28 % respectively. Wear and corrosion resistance improved with the increase of FSP passes. The quantitative results of the study strongly corroborate with microstructural evolution.

Enhanced strength ductility and wear resistance in a friction stir processing engineered AZ31B/TiC magnesium-based nanocomposites

ABSTRACTIn the present investigation, efforts have been made to fabricate a magnesium-based AZ31B nanocomposite by integrating nano-sized titanium carbide (TiC) particles via utilising the friction stir processing (FSP) process. The primary objective of the research was to enhance the metallurgical, mechanical, and tribological properties of the base material while investigating the influence of secondary phase particles and various FSP parameters. The findings were rigorously validated through a comprehensive analysis, which encompassed the use of various testing apparatus, such as optical microscopy, field emission scanning microscopy, microhardness testers, tensile and compressive testing machines, along with fractography analysis for wear morphology and tensile properties. The results indicate that the nanocomposite produced under the conditions of a tool rotation speed of 1600 rpm and a transverse speed of 40 mm/min along with three number of FSP passes exhibits superior mechanical and tribological properties compared to both other developed composites and the base alloy. A significant enhancement of nearly 2.68 times in microhardness values along with simultaneous refinement in grain size up to 14.85 times was obtained. Ultimate tensile and compressive strengths report an impressive increase in values up to 2.16 and 1.6 times respectively when compared to the base metal. Furthermore, the tensile fracture behaviour of the base magnesium alloy indicated brittleness, while the AZ31B/TiC composite displayed a combination of ductile and brittle features. In terms of wear morphology, the base magnesium alloy exhibited adhesive and abrasive wear, while the composite demonstrated particle pull-out, delamination, and localised plastic deformation, with enhanced resistance to wear. These findings underscore the significant improvements achieved in mechanical and tribological properties, thus emphasising the novel contributions of this research to the field.

Effects of friction stir processing and nano-hydroxyapatite on the microstructure, hardness, degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications

Nowadays, magnesium alloys are emerging in biomedical implants for their similar properties to natural bones. However, the rapid degradation of magnesium alloys in biological media hinders successful implantation. Refinement of microstructure, as well as reinforcement particles can significantly improve the degradation rate. In this work, multi-pass friction stir processing (FSP) was proposed to synthesize WE43/nano-hydroxyapatite (nHA) surface composite, the microstructure, reinforced particle distribution, micro-hardness, corrosion behavior and in-vitro bioactivity were studied. The subsequent FSP passes of WE43 alloy and WE43/nHA composite refined the grain size which was reduced by 94.29% and 95.92% (2.63 and 1.88 µm, respectively) compared to base metal after three passes. This resulted in increasing the microhardness by 120% (90.86 HV0.1) and 135% (105.59 HV0.1) for the WE43 and WE43-nHA, respectively. It is found that increasing FSP passes improved the uniform distribution of nHA particles within the composite matrix which led to improved corrosion resistance and less degradation rate. The corrosion rate of the FSPed WE43/nHA composite after three passes was reduced by 38.2% (4.13 mm/year) and the degradation rate was reduced by 69.7% (2.87 mm/y). This is attributed to secondary phase (Mg24Y5 and Mg41Nd5) particle fragmentation and redistribution, as well as a homogeneous distribution of nHA. Additionally, the growing Ca-P and Mg(OH)2 layer formed on the surface represented a protective layer that reduced the degradation rate. The wettability test revealed a relatively hydrophilic surface with water contact angle of 49.1 ± 2.2° compared to 71.2 ± 2.1° for base metal. Also, biomineralization test showed that apatite layer grew after immersion 7d in simulated body fluid with atomic ratio of Ca/P 1.60 approaching the stoichiometric ratio (1.67) indicating superior bioactivity of FSPed WE43/nHA composite after three passes. These results raise that the grain refinement by FSP and introduction of nHA particles significantly improved the degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications.

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.

Friction stir processing of AZ31 alloy to improve the mechanical, biodegradation, and in vitro biocompatible characteristics

The aim of the study was to improve the mechanical, biodegradation and in vitro biocompatible characteristics of as received rolled AZ31 (Mg-1%Zn-3%Al) alloy by develop the surface composite of Mg-Titania. The surface composite was developed by friction stir processing (FSP) and it’s used for prosthetic applications. The influence of tool rotation speed and number of FSP passes on grain structure, grain refinement, tensile strength, hardness, in vitro degradation rate and in vitro biocompatibility were explored. The obtained results support the capability of FSP in terms of mechanical strengthening, refinement of grain structure, dispersion of reinforcement (i.e. TiO2) and controlled degradation rate. Grain structure at stir zone, advancing side and retreating side were investigated. The large grains in the alloy were reduced to a fine equiaxial grains of average dimension of ≈ 3 μm by 3rd pass of FSP. The process was performed under two different tool rotation speed, i.e. 1550 and 2260 RPM. The addition of second phase in the matrix significantly improve the grain refinement. The results obtained from tensile test revealed the improvement in the percentage elongation without compromising the strength. The micro hardness of specimens of different parametric combination were evaluated and found ≈ 30–50% improvement in the micro hardness. The degradation rate by immersion test in simulated body fluid (SBF) for 3, 6 and 10 days were performed and found a significant reduction in degradation rate. The MTT assay for the biocompatibility performed by indirect method, the results validate the non-toxic behavior of processed specimen.

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.

Effect of reinforcement particles and multipass of friction stir processing on microstructure and mechanical properties of aluminium alloy

The present study focuses on the successful fabrication of aluminium metal matrix composites (AMMCs) using friction stir processing (FSP) and micro-sized SiC as reinforcement particles (RPs). The microstructure of Al6061-T6/SiC AMMCs in the stir zone was examined using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). The incorporation of SiC particles and the refinement of grain structure resulted in upgraded mechanical properties of the AMMCs achieved through three FSP passes. These enhancements were concerning from the reduction in grain size and more orderly dispersal of SiC particles. Moreover, the microhardness of the AMMCs enhanced by 41.79%, by augmenting the FSP passes, which can be characterized by the refinement in grain structure, facilitated by the dynamic recrystallization (DRx) mechanism.

Microstructure and Mechanical Properties of 2024 Aluminum Alloy with and Without Rare-Earth and Thermomechanical Treatment After Multi-pass Stir Friction Processing

Friction stir processing (FSP) is the most effective severe plastic deformation process for creating materials with very fine grains and good properties. The target of the present research is to investigate the influence of FSP on the microstructure and mechanical properties of homogenized 2024 aluminum alloy with and without rare-earth (RE) and thermomechanically treated conditions (TMT). The rare-earth elements used were Ce and La in the form of a master alloy containing (50% Ce + 50% La). The casting of 2024 aluminum alloys, both with and without (Ce + La), was carried out using the conventional stir cast technique. Part of the obtained alloys was homogenized, whereas the other part was thermomechanically treated (TMT). The homogenized 2024 material was exposed to FSP with multiple passes (one, two, and three) to obtain the suitable pass number. After that, the best pass number was performed on the 2024 aluminum alloy refined with RE (Ce + La) and TMT materials. The microstructures in different conditions (homogenized and stir friction) were examined by optical and scan microscopes attached with EDS and Map analyzer. At the same time, a tensile test was conducted to assess the mechanical properties. The findings indicated that the microstructures were significantly refined after adding RE (Ce + La) or applying the TMT technique. Whereas, the microstructures were greatly improved after applying FSP to both conditions. Ultra-fine grains were observed for both TMT and RE-containing alloys after FSP. On the other hand, the results of mechanical properties were significantly increased after applying multiple passes of FSP. The optimum results were obtained when two passes of stir friction were applied to the TMT alloy condition.

Fabrication of Al matrix composite reinforced with Fe-Cu particles using friction stir processing

Friction stir processing (FSP), as an advanced technique, was employed to fabricate in situ aluminum composites with the aim to elucidate the correlation between microstructure and mechanical properties of the obtained composites. The novelty of the work is to utilize simultaneous incorporation of Fe and Cu powders into the friction stir zone in order to fabricate in situ aluminum composites. To achieve the goal, the loading content of Cu and Fe powders and the process pass number (1 pass to 5 passes) were altered. While the total loading content of Fe and Cu powders was kept constant, the weight percentages of these reinforcements were varied (25%, 50%, and 75%). Microstructural characteristics were examined using scanning electron microscopy and optical microscopy. Five passes FSP resulted in smaller grain sizes of the Al matrix, smaller and less agglomeration of the reinforcements as well as homogeneous dispersion of the reinforcement features and thus, enhancement of the mechanical properties of the composites. X-ray analysis and energy dispersive spectroscopy confirmed in situ formation of Fe-Al and Al-Cu intermetallic compounds in the composites. The tensile testing outcomes proposed the 50wt% Fe-50wt% Cu/Al composite fabricated in 5 passes as the optimum formulation achieved in this research. This can be attributed to the smaller grain size of the matrix in the friction stirred zone and more homogeneous dispersion of the reinforcements in the matrix. Furthermore, this strengthening was affected from the presence of more amounts of well dispersed intermetallic compounds in situ formed during 5 passes. The average tensile strength (207 MPa) and hardness (73 Vickers) of the composite were approximately 175% and 160% greater than that of the unreinforced aluminum (75 MPa, 28 Vickers), respectively. Increasing the process pass number from 3 to 5 passes not only had strengthening and hardening effects but also improved the composite elongation at break.

Microstructure and mechanical properties of tungsten inert gas welded dissimilar aluminum alloys joint subjected to normal multi-pass friction stir process

This work investigated the effect of multi-pass friction stir processing on the tungsten inert gas welded joints of AA6082/AA8011. The friction stir processing approach is broadly used in the marine, automotive, and aerospace engineering sectors. The flow of plasticized material seems to be significant in the mixed flow region, which causes an erratic intercalation pattern. By using a stirring tool action, deformation was induced in situ extrusions of dissimilar alloys. The plasticized material was moved layer by layer to generate a lamellae structure. Theparent materials AA6082 and AA8011 were seen to be penetrating and vigorously mixing in this zone. After the fourth pass friction stir processing, the tungsten inert gas weldment's ultimate tensile strength and % strain dramatically increased. The defects that had been present before friction stir processing were eliminated when the coarse grain structure of the tungsten inert gas weldments was changed into a refined grain structure from 18.09 to 8.92 µm. The microstructure study shows the linear relationship between friction stir processing passes and grain size. The increases in friction stir processing pass resulted in a decrease in grain size. The maximum ultimate tensile strength (89.60) was observed in tungsten inert gas + 4 pass friction stir processing compared to the other joints.

Influence of pass number on microstructure, mechanical, and tribological properties of cold-rolled Al1050 during friction stir processing

In this investigation, cold-rolled Al1050 sheets underwent various passes of Friction Stir Processing (FSP), namely one, three, and five. Then, microstructural evolution was assessed by focusing on underlying restoration phenomena, including severe dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), and their corresponding effects on mechanical and surface properties were evaluated. Findings illustrated that initial cold-rolling on Al1050 and its high stacking fault energy are the primary driving forces for accelerating DRV, contributing to the supremacy of the DRV-induced softening over sub-grain strengthening caused by CDRX. Increasing the FSP pass number resulted in a drop in yield stress (YS), ultimate tensile strength (UTS), and microhardness values of the FSP-treated samples such that the UTS of one, three, and five passes FSPed samples decreased by ∼18 %, 32 %, and 35 %, respectively, compared to the cold-rolled Al1050. Conversely, the %elongation of the FSP-treated samples dramatically increased with increasing FSP pass number, which is evident from stress-strain curves and the fracture surfaces. Furthermore, increasing the FSP pass number increased the mean coefficient of friction (MCOF) and weight loss during the pin-on-disk test. Also, conducting various passes of FSP improved corrosion resistance compared to the base metal. However, increasing the FSP pass number reduced the corrosion resistance due to grain growth such that the one-pass FSPed sample illustrated better corrosion resistance than the five passes FSPed sample. Repeating the FSP led to excessive frictional heat input to the matrix, contributing to grain growth after increasing FSP passes, thereby decreasing mechanical properties and corrosion resistance.