Influence of process parameters on wear resistance of surfaces modified by friction stirring processing in 7075 aluminum alloy

Influence of process parameters on wear resistance of surfaces modified by friction stirring processing in 7075 aluminum alloy | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of process parameters on wear resistance of surfaces modified by friction stirring processing in 7075 aluminum alloy JiangTao Wang, Aoxiang Liu, YongKang Zhang, Li Xie, MingTao He, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4258326/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract This work investigated effects of friction stirred processing (FSP) parameters on the wear resistance of 7075 aluminum alloy. The results indicate the significantly higher wear rate and average coefficient of friction during the stabilization stage of samples W1 (welding speed: 60 mm/min; rotation speed: 1000 rpm) and W8 (welding speed: 80 mm/min; rotation speed: 1200 rpm), with increases of 45% and 40% for the wear rate, respectively, and 19% and 13% for coefficient of friction in comparison with the untreated material. The optimized FSP parameters can considerably improve the wear resistance of the material by affecting the heat input, which altered the grain size and distribution in the welded zone. X-Ray diffraction and scanning electron microscopy/energy dispersive spectroscopy studies provided the mechanism underlying grain size and plastic nano twin structures contributions to wear resistance. Wear resistance process parameters FSP 7075 aluminum alloy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction The 7075 aluminum alloy is extensively applied in aerospace, marine machinery, and other domains owing to its low density, high strength, and high specific strength[ 1 – 3 ]. Nonetheless, the material exhibits susceptibility to wear and other forms of damage under reciprocating motion conditions, which consequently diminish the longevity of the workpiece. Hence, improving the wear-resistant characteristics of the workpiece holds importance in prolonging its service life and facilitating the broader utilization of aluminum alloy. The friction stirred welding (FSW) process refers to a solid-phase welding technique used to join two plates through a butt-welding process. Friction stirred processing (FSP), as an advanced version of FSW, operates on the same fundamental principle; however, this method exclusively focuses on the modification of the workpiece surface[ 4 ]. Scholars have carried out a considerable amount of research on tribology via the FSP process. Li et al.[ 5 ] discovered that the utilization of a double-needle stirrer head resulted in a 22% reduction in the average particle size of the weld tissue. Furthermore, they enhanced the wear resistance of AA6061/316 by varying the number of stirrer needles (from single to double) for the FSP process. Zhu et al.[ 6 ] prepared copper-matrix surface composites (HEA/Cu) by incorporating high-entropy alloy particles (HEA). The resulting material exhibited a notable increase in hardness, which was 69.8% higher than that of the original parent material after FSP processing. In addition, the wear rate of the composite was reduced by 29.7%, which demonstrates its superior wear resistance compared with the original material. Shazman et al.[ 7 ] observed noteworthy decreases of 17% and 15% in the coefficient of friction when subjected to loads of 15 and 25 N, respectively. These results were attributed to the incorporation of reinforced NiTip in Al-5052/NiTip alloys through a multipass FSP process, which indicates a notable improvement in the frictional characteristics of the material. In the aforementioned study, the inclusion of a reinforcing phase resulted improved the wear resistance of the welds after FSP. Building upon this finding, this paper examined the wear resistance of welds made from 7075 aluminum alloy through modification of the parameters of FSP and investigated the underlying mechanism behind the improved wear resistance. 2 Materials and methods Rolled commercial metal sheets of a 7075-T6 aluminum alloy with a thickness of 5 mm were utilized, and welded plates with dimensions of 300×100×5 mm were cut from them. Prior to FSP, the workpieces were meticulously cleaned and stored in a vacuum drying box as a precautionary measure. A FSW equipment (FSW-RT31-003 model, Beijing Safest Company, Beijing) was employed in the welded experiment. The workpiece was positioned on the fixture Fig. 1 (a). In order to assess the effect of process parameters on wear resistance, we classified them into three groups (Table 1 ). The tribological and microstructural specimens were prepared with dimensions of 10 × 10 × 5 and 18 × 5 × 5 mm, respectively Fig. 1 (c). A friction and wear tester model (CETR UMT-2MT) was used to conduct linear reciprocating friction and wear experiments on the specimens with various FSP parameters Fig. 1 (d). GCr15 steel balls measuring 6 mm in diameter and possessing a hardness of HRC65 were utilized. The experiments were conducted under the following conditions: room temperature, an applied load of 20 N, rotational speed of 120 r/min, frequency of 1 Hz, stroke length of 5 mm, and duration of 15 min. A high-resolution field emission scanning electron microscope (Sigma 500 model) was employed to observe wear marks and abrasive debris and conduct elemental analysis (energy dispersive spectroscopy (EDS)). Furthermore, an X-ray diffractometer (X’pert Pro model) was utilized to perform physical-phase analysis (X-ray diffraction (XRD)) of the specimens before wear. Table 1 FSP process parameters Order Number Welding speed /(mm/min) Rotation speed /rpm Order Number Welding speed /(mm/min) Rotation speed /rpm Order Number Welding speed /(mm/min) Rotation speed /rpm W1 60 1000 W4 70 1000 W7 80 1000 W2 60 1200 W5 70 1200 W8 80 1200 W3 60 1400 W6 70 1400 W9 80 1400 3 Results and discussion 3.1 Phase analysis Figure 2 presents the XRD results of the untreated and FSPed specimens. The presence of α-Al (face-centered cubic structure) and MgZn2 phases (η) in the BM and FSPed specimens signifies the characteristic crystal structure. As shown in Fig. 2 (a), compared with those of the FSPed material, the diffraction peak intensities and half-height widths of the (200) crystalline plane of the parent material were consistently larger, and those of the (111) crystalline plane were constantly smaller. Figure 2 (f) shows that compared with the (111) grain surface, the (200) grain surface of the untreated specimens exhibited a higher diffraction peak intensity, whereas that of the FSPed (200) grain surface was consistently lower. Severe plastic deformation and dislocation slip occurred in the 7075 aluminum alloy during FSP, and the latter did not lead to transformation of crystal orientation. Specifically, after FSP, the most prominent diffraction peaks of the 7075 aluminum alloy shifted from the (200) crystal plane to the (111) crystal plane. This finding signifies that twinning behavior occurred within the inner part of the aluminum alloy following FSP [ 8 ]. Thus, dislocation slip can induce twin formation. To investigate the effect of various process parameters, three sets of data were compared Figs. 2 (b)–(d). As the welded speed increased, the 2θ angle remained relatively constant, the half-height width gradually decreased, and the diffraction peak intensities of the (111), (200), (220), (311), and (222) crystal planes initially increased and then decreased. Notably, among M1–M3, the (111) crystal plane attained the highest intensity at approximately 38°. Upon close examination of the precipitation phases depicted in Fig. 2 (e), the peak intensity increased notably within the range of 40.5°–41.5° for the specimens subjected to FSP. The content of MgZn2 in the FSPed specimens was influenced correspondingly. Further scrutiny of the (201) and (004) crystal surfaces revealed that the peak intensity of the W8 specimen surpassed that of the other two. This discrepancy can be attributed to the high rotational speed implemented during FSP, which resulted in an augmented heat input [ 9 ]. Consequently, the elevated temperature facilitated the dissolution of the MgZn2 phase. These findings suggest grain refinement in the FSPed specimen Fig. 1 (c). In addition, the microstructure of aluminum alloy varied from an evident untreated rolled-strip structure to a fine equiaxed crystal structure after rolling. 3.2 Tribology analysis Figure 3 exhibits the results regarding the coefficient of friction and wear rate for different process parameters. The figure illustrates that the friction coefficient generally increased with an increase in rotational speed at a welded speed of 60 mm/min but decreased at 70 mm/min. The friction coefficient curves revealed oscillations and fluctuations at a welded speed of 80 mm/min Fig. 3 (c). Notably, the friction coefficient gradually increased with the increase in welded speed, and some specimens subjected to FSP treatment exhibited a lower friction coefficient compared with the untreated ones Fig. 3 (d). Furthermore, during the comparison and analysis of the average friction coefficients during the stabilization stage, W1 and W8 showed relatively small friction coefficients. The wear rate, which is a crucial indicator for the assessment of wear performance, is calculated using Eq. (1–1) [ 10 ]: $$\begin{array}{c}\text{W}\text{r}\text{ }\text{=}\text{ }\frac{\text{A·L}}{\text{F·S}}\#（\text{1-1}）\end{array}$$ where Wr refers to the specific wear rate (mm3/Nm), A indicates the cross-sectional area of the abrasion mark (mm2), L denotes the single-friction sliding distance set during friction (mm), F represents the normal load applied during friction (N), and S corresponds to the total sliding stroke throughout the friction process (m). Figure 3 (f) illustrates that under various process parameters, the wear rate exhibited an initial decrease followed by an increase and a final decrease. The wear rate of W7 was comparatively higher than those of other specimens. This promotion can be mainly affected by rotational speed, which is a key parameter in FSP. A high rotational speed results in increased heat input, which in turn leads to a coarse grain size[ 11 , 12 ] Fig. 1 (c3). A coarse grain size subsequently affects weld properties. The occurrence of microcracks during reciprocating wear is a well-established phenomenon[ 13 ]. Furthermore, the likelihood of crystal fracture is directly proportional to grain size, with large grain sizes presenting a high risk. Consequently, coarse grains possess few grain boundaries, which enable crack propagation along these boundaries and ultimately give rise to wear chips[ 14 ]. Conversely, small grains also exhibit crack formation during the wear process. However, given the larger number of crystal surfaces in comparison with coarse grains, these cracks encounter greater difficulty in expansion. Consequently, for the enhanced wear resistance of materials, it appropriate process parameters should be used. 3.3 Analysis of abrasive marks and chips To further explore the wear performance, we observed the abrasion marks of the untreated and FSPed specimens Fig. 4 . Every specimen exhibited spalling pits, which varied in terms of number and size. This discrepancy suggests the severe plastic deformation involved in the friction wear process. In addition to the spalling pit area, other regions displayed evident furrowing phenomena. The abrasion process resulted in the presence of hard abrasive grains, with a portion of abrasive debris adhering to the substrate over an extended duration and subsequently undergoing oxidation upon contact with air. Under the influence of the load and contact with the soft substrate, these abrasive grains caused the formation of furrows, which indicates that the form of wear failure was abrasive wear. Furthermore, an assessment of the maximum width of abrasion marks revealed the smallest width in M1 (1520 µm). Conversely, M7 demonstrated the largest ink mark width of 1960 µm. Notably, the BM attained an abrasion mark width of 1887 µm, which is markedly smaller compared with those of other parameters, except for M7. Nevertheless, the results of comprehensive morphological analysis of abrasion mark width are not necessarily indicative of the superior abrasion resistance of the W3 process parameters. Consequently, a closer examination of the blue box depicted in Fig. 4 was conducted. Examination of the images within the specified blue box Fig. 4 revealed abrasive grains of varying sizes and furrows of differing depths for each process parameter. Figures 5 (h) and (j) show large fragments of abrasive debris that had not been dislodged. EDS elemental analysis of the former revealed the presence of oxygen and a small quantity of iron, which indicates that some damage was inflicted upon the GCr steel ball during abrasion. Further observation of the wear marks revealed the delamination, cratering, and formation of a plastic deformation layer, which signify the presence of adhesive wear. In conjunction with the abrasive wear phenomenon depicted in Fig. 4 , the weld produced via FSP experienced failure in the form of abrasive and adhesive wear. Furthermore, the presence of surface cracks on the abrasion marks suggests the generation of abrasive debris in this region. During the reciprocal wear process, the GCr steel ball abraded the weld seam, and this phenomenon can be metaphorically described as the ball milling of the FSPed specimen. In reciprocal friction, the steel ball generated frictional heat on the specimen, which caused softening of the material near the surface. Consequently, a cutting phenomenon was observed with the contact and relative motion between the harder and softer materials, which led to the formation of abrasive debris. Under frictional heat, the abrasive debris was highly prone to oxidation, as demonstrated by its energy spectrum in Fig. 5 (a). In addition, the abrasive chips observed in the wear experiments served as a supplementary indicator of wear performance Fig. 6 . Comparison of the average sizes of the wear chips in W1 and W8 with other sets of chips revealed the smaller chip sizes of the former Figs. 6 (b) and (h). This result can be attributed to the plastic deformation of the material’s surface layer caused by ball wear, which led to grain fragmentation. As mentioned earlier, the superheat input affected grain size during FSP, which resulted in small chip sizes during the breakage of small grains. 3.4 Mechanistic analysis The above findings reveal the correlation between heat input and wear resistance. In addition, we have identified a crucial relationship between rotational speed and heat input, and this connection is intricately linked to grain size. This observation aligns with the calculations derived using the FSW formula (1–2) for heat generation[ 15 ]: $$\text{ }\text{Q}\text{ =}\frac{\text{πμnp}\left({{\text{R}}_{\text{1}}}^{\text{2}}\text{+}{\text{R}}_{\text{1}}{\text{R}}_{\text{2}}\text{+}{{\text{R}}_{\text{2}}}^{\text{2}}\right)}{\text{45}\left({\text{R}}_{\text{1}}\text{+}{\text{R}}_{\text{2}}\right)\text{v}}\text{ }\text{ }\text{ (1-2)}$$ where Q refers to the heat input to the workpiece, v is the welded speed, R 1 and R 2 denote the shoulder radius of the stirring needle and the stirring needle radius, respectively. n indicates the rotational speed of the stirring needle, P represents the welding pressure, and µ is the friction coefficient. Eq. (1–2) demonstrates that the frictional heat Q generated by the workpiece depends on rotational speed n and welded speeds v . Furthermore, these parameters, along with a certain amount of downward pressure, affect the axial force P exerted on the workpiece. The axial force, in turn, influences the subsequent heat of deformation and ultimately the weld head quality. The process parameters examined in this research paper comprise the rotational and welded speeds, whereas the other parameters remained constant. The heat input Q is determined by the ratio of rotational speed to welded speed, that is, Q is directly proportional to the value of n / v . Comparison of heat inputs across different data sets, as depicted in the line graph in Fig. 7 , revealed that for a given welded speed, an increase in rotational speed led to increased heat input and grain size. Moreover, the amount of wear increased compared with the results displayed in Fig. 3 (f). However, W8 exhibited a considerable decrease in wear, followed by the increased wear of W9. Zhang et al.[ 11 ] mentioned that heat input also affects grain size, with excessive input leading to large grains and insufficient input resulting in weld defects. The heat inputs for specimens W1, W4, W7, W8, and W9 were 16, 14, 12.5, 15, and 17.5 (J/mm), respectively. Figures 3 (d) and 4(f) provide supporting evidence showing the similarities of the coefficients of friction and wear rates of W1 and W8. This finding further substantiates the importance of a heat input of approximately 16 J/mm (blue dashed line and red triangle in Fig. 7 ). Figure 8 shows the internal microstructure after friction stirred processing. It is well known that nano-twinning exists in materials with low level of dislocation energy[ 16 ], and 7075 aluminum alloy belongs to the materials with high level of dislocation energy, which is not conducive to the formation of nano-twinning. However, after friction stir processing, the dislocations are accumulated due to the intense plastic deformation, as shown in Fig. 8 (a)-(c). Moreover, the higher rotational speed makes 7075 aluminum alloy less prone to dislocation migration, so that the twin structure appears internally after stirring and friction processing, as shown in Fig. 8 (d). The experimental results of the plastic nano twin structures are in good accordance with those findings based on XRD. The Fourier transform (FFT) of the grain organization in Fig. 8 (e) yields a grain spacing of 0.83 nm and 0.44 nm, respectively. In addition, the HRTEM image shows an atomic-scale twin structure with a twin size of about 3.33 nm, as shown in Fig. 8 (h) and (i). Generally, it is difficulty to form twins in Al alloy microstructure because it belongs to FCC metals with high stacking fault energy (86 mJ/m2)[ 17 , 18 ]. Owing to the high strain rate induced by FSP, the dislocation movement velocity is fast, resulting in dislocation accumulation, which is more prone to the nucleation of deformation twins. The presence of twin crystals not only improves the toughness of the weld after friction stirred processing, but also reduces the fatigue damage of the material. In addition, since the twin crystals can lead to the stress distribution on the material surface to become more uniform[ 19 ], the material will be able to reduce the crack expansion rate during the reciprocating motion. Liu and his co-workers[ 20 ]revealed that the enhanced wear resistance performance of NiCoFeCrMoW were also due to the existence of a large number of deformation twins. Simultaneously, Chen et al.[ 21 ] proposed a promising approach to introduce twins in ceramic films and enhance the wear resistance performance of the Si matrix. Conclusion The friction and wear characteristics and mechanism of various FSP parameters were analyzed via XRD, SEM technology, etc. The primary findings of this research are summarized as follows: (1) Grains were refined after FSP treatment compared with the BM. However, the process parameters directly affected the microstructure. Especially, W8 exhibited better welded and rotation speeds (80 and 1200 rpm, respectively) than W2 (60 and 1200) and the smaller and more uniform distribution of grains in the weld zone. And the microstructure was accompanied by the generation of a large number of highly plastic nano twin structures. (2) After FSP, the wear resistance of specimens was improved, and the average coefficient of friction in the stabilization phase of W1 and W8 increased by 19% and 13%, respectively, compared with those of the BM. The wear rates of W1 and W8 increased by 45% and 40%, respectively, compared with that of the BM. The wear mechanisms were abrasive and adhesive wear. And the formation of nano twin structure greatly enhances the adhesive wear resistance of FSPed specimens. (3) Rotational speed is directly proportional to heat input, and wear resistance with heat input showed a trend opposite that of grain size, which is the main factor affecting the wear resistance of FSPed specimens. Thus, after evaluation of the combined properties and welding efficiency, the optimal process parameter was determined to be a rotational speed of 1000 − 200 rpm at a certain welding speed, which can provide an optimized heat input of 15–16 J/mm. Declarations Acknowledgments The authors are grateful for the support provided by the Natural Science Major Foundation of the Jiangsu Higher Education Institutions (Grant No.19KJA460003), the National Natural Science Foundation of China (Grant No.52205157). ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: References Mirjavadi SS, Alipour M, Hamouda AMS et al (2017) Effect of multi-pass friction stir processing on the microstructure, mechanical and wear properties of AA5083/ZrO2 nanocomposites[J]. J Alloy Compd 726:1262–1273 Moustafa EB, Mosleh AO (2020) Effect of (Ti–B) modifier elements and FSP on 5052 aluminum alloy[J]. 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Acta Mater 257:119189 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 04 Jun, 2024 Reviewers invited by journal 17 May, 2024 Editor invited by journal 18 Apr, 2024 Editor assigned by journal 16 Apr, 2024 First submitted to journal 15 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4258326","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":303547012,"identity":"d99c033f-54b0-4e6f-b291-71c74396884e","order_by":0,"name":"JiangTao Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIie3PIQvCUBDA8RsHb+Xw1TccfoYHwiyCX+WNwdIE48LCBqJB7fotjMbJYOnZbbpi1mYSZ1bcbIb3SxfuD3cAhvGHOgDWWcUJcTvLXkNzwgBQXnXpOsuikGddtkqYs5nhUB7D0Kmm2CKxtewSYwR55MV+yoDPF+p7QqHqE7lkpdo7+jsXhD5sGw4L8oAEI7SWdaIZSDFuSHiVFiSRGJI38WfYIhHBPlsrpPqfEFomlwCueUmCsBBK10PTL5xHg7v/SEajU5Xd7nHS4/PV9+QN/bZuGIZhfPQEU8BEcvzmFycAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0000-4808-6075","institution":"Jiangsu University of Technology","correspondingAuthor":true,"prefix":"","firstName":"JiangTao","middleName":"","lastName":"Wang","suffix":""},{"id":303547013,"identity":"7f840feb-6eba-44c4-ab76-eaf210f6cf7d","order_by":1,"name":"Aoxiang Liu","email":"","orcid":"","institution":"Jiangsu University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Aoxiang","middleName":"","lastName":"Liu","suffix":""},{"id":303547014,"identity":"bf5b2e67-8453-4767-8ef6-b554e5110715","order_by":2,"name":"YongKang Zhang","email":"","orcid":"","institution":"Guangdong University of Technology","correspondingAuthor":false,"prefix":"","firstName":"YongKang","middleName":"","lastName":"Zhang","suffix":""},{"id":303547015,"identity":"368d8079-394d-4083-8a82-b5f785d41c61","order_by":3,"name":"Li Xie","email":"","orcid":"","institution":"Jiangsu University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Xie","suffix":""},{"id":303547016,"identity":"29e39f1a-cd6c-4a4d-a868-b6f25bd15000","order_by":4,"name":"MingTao He","email":"","orcid":"","institution":"Jiangsu University of Technology","correspondingAuthor":false,"prefix":"","firstName":"MingTao","middleName":"","lastName":"He","suffix":""},{"id":303547017,"identity":"0540728a-36d7-40a5-9a40-5326de3a0bb6","order_by":5,"name":"KaiYu Luo","email":"","orcid":"","institution":"Jiangsu University","correspondingAuthor":false,"prefix":"","firstName":"KaiYu","middleName":"","lastName":"Luo","suffix":""},{"id":303547018,"identity":"18459a83-f074-4dc5-9d33-3998d8f022d6","order_by":6,"name":"KeJun Hu","email":"","orcid":"","institution":"Jiangsu University of Technology","correspondingAuthor":false,"prefix":"","firstName":"KeJun","middleName":"","lastName":"Hu","suffix":""}],"badges":[],"createdAt":"2024-04-12 14:21:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4258326/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4258326/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57628375,"identity":"98122a7a-1642-4acb-9df6-0ef99dba2ecd","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1202600,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Equipment and fixtures, (b) schematic of tribological and microstructural specimens, (c) microstructure of base material (BM) [ (c1)] and FSPed [(c2 and c3)], and (d) tribological specimen and abrasion mark characteristics [tribological specimen in (b)]\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/d29f11a67bd0e46a7d7322cf.png"},{"id":57629679,"identity":"ddd469a7-1489-486a-b8db-c843f4020114","added_by":"auto","created_at":"2024-06-03 14:37:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":274696,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD summary diagram, (b) welded speed of 60 mm/min, (c) welded speed of 70 mm/min, and (d) welded speed of 80 mm/min. (e) BM with magnified view of the precipitated phase in (d). (f) Plot of main peak data in (a) and (g) plot of precipitated phase data in (e)\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/ac92c1aee85d449747ba0ba1.png"},{"id":57628373,"identity":"7abb6fda-94eb-40e1-b103-7947947a86bf","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":257257,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient results on (a) W1–W3, (b) W4–W6, (c) W7–W9, and BM (d). (e) Average friction coefficient in stable stage. and (f) Wear rate.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/f94350e20d40c9bc89bc8435.png"},{"id":57629680,"identity":"509cc079-8124-44d4-b1d7-0c9d28737352","added_by":"auto","created_at":"2024-06-03 14:37:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1039013,"visible":true,"origin":"","legend":"\u003cp\u003e(a)–(j) Whole images of W1–BM wear marks, respectively (the blue box corresponds to the local enlargement of Fig. 5).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/fd4fdb196317686feafb07bb.png"},{"id":57628376,"identity":"19f296b6-ac9c-49af-b4cc-6400e9c92308","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1251331,"visible":true,"origin":"","legend":"\u003cp\u003e(a)–(j) Local magnification of the wear marks in the blue box in Fig. 4. (k) Energy spectrum of Fig. 5(h)\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/05ee74c6b26c41088e000cab.png"},{"id":57628380,"identity":"ab13d377-cc07-4d17-b576-8683a81b6d70","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":854282,"visible":true,"origin":"","legend":"\u003cp\u003e(a)–(j) scanning electron microscopy (SEM) of wear debris generated by W1–BM during friction and wear, respectively. (k) Corresponding local element analysis of Figs. 5(b), 5(h) and 5(j), respectively.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/101862c5009dcee65abdedf7.png"},{"id":57628377,"identity":"19335d13-0730-43aa-a670-84b5264b0466","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":319784,"visible":true,"origin":"","legend":"\u003cp\u003eMechanistic analysis of rotational speed during heat input (the line graph depicts the heat input for each specimen).\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/62416e73c7f15a91430ebba2.png"},{"id":57628379,"identity":"f4452bd8-196b-4085-b222-835a7715bd8b","added_by":"auto","created_at":"2024-06-03 14:29:33","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1487928,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Dislocations accumulation at grain boundary (b) and (c) Dislocation mesh structures (d) Twin structure (e) Substrate and twin structure (f) and (g) Interplanar spacing size in (e) (h) Twin HRTEM image (i) Electron diffraction pattern of twin\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/f53a410dd9fcaadd8388dca7.png"},{"id":57630365,"identity":"ee1a062a-4855-4db4-97d8-a8eb33eaa1ee","added_by":"auto","created_at":"2024-06-03 14:45:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8165075,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4258326/v1/07f30d2c-c284-4982-8fd1-70964f388148.pdf"}],"financialInterests":"","formattedTitle":"Influence of process parameters on wear resistance of surfaces modified by friction stirring processing in 7075 aluminum alloy","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe 7075 aluminum alloy is extensively applied in aerospace, marine machinery, and other domains owing to its low density, high strength, and high specific strength[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Nonetheless, the material exhibits susceptibility to wear and other forms of damage under reciprocating motion conditions, which consequently diminish the longevity of the workpiece. Hence, improving the wear-resistant characteristics of the workpiece holds importance in prolonging its service life and facilitating the broader utilization of aluminum alloy. The friction stirred welding (FSW) process refers to a solid-phase welding technique used to join two plates through a butt-welding process. Friction stirred processing (FSP), as an advanced version of FSW, operates on the same fundamental principle; however, this method exclusively focuses on the modification of the workpiece surface[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Scholars have carried out a considerable amount of research on tribology via the FSP process. Li et al.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] discovered that the utilization of a double-needle stirrer head resulted in a 22% reduction in the average particle size of the weld tissue. Furthermore, they enhanced the wear resistance of AA6061/316 by varying the number of stirrer needles (from single to double) for the FSP process. Zhu et al.[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] prepared copper-matrix surface composites (HEA/Cu) by incorporating high-entropy alloy particles (HEA). The resulting material exhibited a notable increase in hardness, which was 69.8% higher than that of the original parent material after FSP processing. In addition, the wear rate of the composite was reduced by 29.7%, which demonstrates its superior wear resistance compared with the original material. Shazman et al.[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] observed noteworthy decreases of 17% and 15% in the coefficient of friction when subjected to loads of 15 and 25 N, respectively. These results were attributed to the incorporation of reinforced NiTip in Al-5052/NiTip alloys through a multipass FSP process, which indicates a notable improvement in the frictional characteristics of the material. In the aforementioned study, the inclusion of a reinforcing phase resulted improved the wear resistance of the welds after FSP. Building upon this finding, this paper examined the wear resistance of welds made from 7075 aluminum alloy through modification of the parameters of FSP and investigated the underlying mechanism behind the improved wear resistance.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cp\u003eRolled commercial metal sheets of a 7075-T6 aluminum alloy with a thickness of 5 mm were utilized, and welded plates with dimensions of 300\u0026times;100\u0026times;5 mm were cut from them. Prior to FSP, the workpieces were meticulously cleaned and stored in a vacuum drying box as a precautionary measure. A FSW equipment (FSW-RT31-003 model, Beijing Safest Company, Beijing) was employed in the welded experiment. The workpiece was positioned on the fixture Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). In order to assess the effect of process parameters on wear resistance, we classified them into three groups (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The tribological and microstructural specimens were prepared with dimensions of 10 \u0026times; 10 \u0026times; 5 and 18 \u0026times; 5 \u0026times; 5 mm, respectively Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c). A friction and wear tester model (CETR UMT-2MT) was used to conduct linear reciprocating friction and wear experiments on the specimens with various FSP parameters Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d). GCr15 steel balls measuring 6 mm in diameter and possessing a hardness of HRC65 were utilized. The experiments were conducted under the following conditions: room temperature, an applied load of 20 N, rotational speed of 120 r/min, frequency of 1 Hz, stroke length of 5 mm, and duration of 15 min. A high-resolution field emission scanning electron microscope (Sigma 500 model) was employed to observe wear marks and abrasive debris and conduct elemental analysis (energy dispersive spectroscopy (EDS)). Furthermore, an X-ray diffractometer (X\u0026rsquo;pert Pro model) was utilized to perform physical-phase analysis (X-ray diffraction (XRD)) of the specimens before wear.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFSP process parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrder Number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWelding speed /(mm/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRotation speed /rpm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOrder Number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWelding speed /(mm/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRotation speed /rpm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eOrder Number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eWelding speed /(mm/min)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eRotation speed /rpm\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eW4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eW7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eW5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eW8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eW6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eW9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e1400\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e3.1 Phase analysis\u003c/h2\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e presents the XRD results of the untreated and FSPed specimens. The presence of \u0026alpha;-Al (face-centered cubic structure) and MgZn2 phases (\u0026eta;) in the BM and FSPed specimens signifies the characteristic crystal structure. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a), compared with those of the FSPed material, the diffraction peak intensities and half-height widths of the (200) crystalline plane of the parent material were consistently larger, and those of the (111) crystalline plane were constantly smaller. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(f) shows that compared with the (111) grain surface, the (200) grain surface of the untreated specimens exhibited a higher diffraction peak intensity, whereas that of the FSPed (200) grain surface was consistently lower. Severe plastic deformation and dislocation slip occurred in the 7075 aluminum alloy during FSP, and the latter did not lead to transformation of crystal orientation. Specifically, after FSP, the most prominent diffraction peaks of the 7075 aluminum alloy shifted from the (200) crystal plane to the (111) crystal plane. This finding signifies that twinning behavior occurred within the inner part of the aluminum alloy following FSP [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e]. Thus, dislocation slip can induce twin formation. To investigate the effect of various process parameters, three sets of data were compared Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(b)\u0026ndash;(d). As the welded speed increased, the 2\u0026theta; angle remained relatively constant, the half-height width gradually decreased, and the diffraction peak intensities of the (111), (200), (220), (311), and (222) crystal planes initially increased and then decreased. Notably, among M1\u0026ndash;M3, the (111) crystal plane attained the highest intensity at approximately 38\u0026deg;. Upon close examination of the precipitation phases depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(e), the peak intensity increased notably within the range of 40.5\u0026deg;\u0026ndash;41.5\u0026deg; for the specimens subjected to FSP. The content of MgZn2 in the FSPed specimens was influenced correspondingly. Further scrutiny of the (201) and (004) crystal surfaces revealed that the peak intensity of the W8 specimen surpassed that of the other two. This discrepancy can be attributed to the high rotational speed implemented during FSP, which resulted in an augmented heat input [\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. Consequently, the elevated temperature facilitated the dissolution of the MgZn2 phase. These findings suggest grain refinement in the FSPed specimen Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(c). In addition, the microstructure of aluminum alloy varied from an evident untreated rolled-strip structure to a fine equiaxed crystal structure after rolling.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003e3.2 Tribology analysis\u003c/h2\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e exhibits the results regarding the coefficient of friction and wear rate for different process parameters. The figure illustrates that the friction coefficient generally increased with an increase in rotational speed at a welded speed of 60 mm/min but decreased at 70 mm/min. The friction coefficient curves revealed oscillations and fluctuations at a welded speed of 80 mm/min Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(c). Notably, the friction coefficient gradually increased with the increase in welded speed, and some specimens subjected to FSP treatment exhibited a lower friction coefficient compared with the untreated ones Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(d). Furthermore, during the comparison and analysis of the average friction coefficients during the stabilization stage, W1 and W8 showed relatively small friction coefficients. The wear rate, which is a crucial indicator for the assessment of wear performance, is calculated using Eq.\u0026nbsp;(1\u0026ndash;1) [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equa\" class=\"mathdisplay\"\u003e$$\\begin{array}{c}\\text{W}\\text{r}\\text{ }\\text{=}\\text{ }\\frac{\\text{A\u0026middot;L}}{\\text{F\u0026middot;S}}\\#（\\text{1-1}）\\end{array}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere Wr refers to the specific wear rate (mm3/Nm), A indicates the cross-sectional area of the abrasion mark (mm2), L denotes the single-friction sliding distance set during friction (mm), F represents the normal load applied during friction (N), and S corresponds to the total sliding stroke throughout the friction process (m). Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(f) illustrates that under various process parameters, the wear rate exhibited an initial decrease followed by an increase and a final decrease. The wear rate of W7 was comparatively higher than those of other specimens. This promotion can be mainly affected by rotational speed, which is a key parameter in FSP. A high rotational speed results in increased heat input, which in turn leads to a coarse grain size[\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e] Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(c3). A coarse grain size subsequently affects weld properties. The occurrence of microcracks during reciprocating wear is a well-established phenomenon[\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Furthermore, the likelihood of crystal fracture is directly proportional to grain size, with large grain sizes presenting a high risk. Consequently, coarse grains possess few grain boundaries, which enable crack propagation along these boundaries and ultimately give rise to wear chips[\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]. Conversely, small grains also exhibit crack formation during the wear process. However, given the larger number of crystal surfaces in comparison with coarse grains, these cracks encounter greater difficulty in expansion. Consequently, for the enhanced wear resistance of materials, it appropriate process parameters should be used.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e3.3 Analysis of abrasive marks and chips\u003c/h2\u003e\n\u003cp\u003eTo further explore the wear performance, we observed the abrasion marks of the untreated and FSPed specimens Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Every specimen exhibited spalling pits, which varied in terms of number and size. This discrepancy suggests the severe plastic deformation involved in the friction wear process. In addition to the spalling pit area, other regions displayed evident furrowing phenomena. The abrasion process resulted in the presence of hard abrasive grains, with a portion of abrasive debris adhering to the substrate over an extended duration and subsequently undergoing oxidation upon contact with air. Under the influence of the load and contact with the soft substrate, these abrasive grains caused the formation of furrows, which indicates that the form of wear failure was abrasive wear. Furthermore, an assessment of the maximum width of abrasion marks revealed the smallest width in M1 (1520 \u0026micro;m). Conversely, M7 demonstrated the largest ink mark width of 1960 \u0026micro;m. Notably, the BM attained an abrasion mark width of 1887 \u0026micro;m, which is markedly smaller compared with those of other parameters, except for M7. Nevertheless, the results of comprehensive morphological analysis of abrasion mark width are not necessarily indicative of the superior abrasion resistance of the W3 process parameters. Consequently, a closer examination of the blue box depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e was conducted.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eExamination of the images within the specified blue box Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e revealed abrasive grains of varying sizes and furrows of differing depths for each process parameter. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(h) and (j) show large fragments of abrasive debris that had not been dislodged. EDS elemental analysis of the former revealed the presence of oxygen and a small quantity of iron, which indicates that some damage was inflicted upon the GCr steel ball during abrasion. Further observation of the wear marks revealed the delamination, cratering, and formation of a plastic deformation layer, which signify the presence of adhesive wear. In conjunction with the abrasive wear phenomenon depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, the weld produced via FSP experienced failure in the form of abrasive and adhesive wear. Furthermore, the presence of surface cracks on the abrasion marks suggests the generation of abrasive debris in this region. During the reciprocal wear process, the GCr steel ball abraded the weld seam, and this phenomenon can be metaphorically described as the ball milling of the FSPed specimen. In reciprocal friction, the steel ball generated frictional heat on the specimen, which caused softening of the material near the surface. Consequently, a cutting phenomenon was observed with the contact and relative motion between the harder and softer materials, which led to the formation of abrasive debris. Under frictional heat, the abrasive debris was highly prone to oxidation, as demonstrated by its energy spectrum in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e(a). In addition, the abrasive chips observed in the wear experiments served as a supplementary indicator of wear performance Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Comparison of the average sizes of the wear chips in W1 and W8 with other sets of chips revealed the smaller chip sizes of the former Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e(b) and (h). This result can be attributed to the plastic deformation of the material\u0026rsquo;s surface layer caused by ball wear, which led to grain fragmentation. As mentioned earlier, the superheat input affected grain size during FSP, which resulted in small chip sizes during the breakage of small grains.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n\u003ch2\u003e3.4 Mechanistic analysis\u003c/h2\u003e\n\u003cp\u003eThe above findings reveal the correlation between heat input and wear resistance. In addition, we have identified a crucial relationship between rotational speed and heat input, and this connection is intricately linked to grain size. This observation aligns with the calculations derived using the FSW formula (1\u0026ndash;2) for heat generation[\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]:\u003c/p\u003e\n\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n\u003cdiv id=\"FileID_Equb\" class=\"mathdisplay\"\u003e$$\\text{ }\\text{Q}\\text{ =}\\frac{\\text{\u0026pi;\u0026mu;np}\\left({{\\text{R}}_{\\text{1}}}^{\\text{2}}\\text{+}{\\text{R}}_{\\text{1}}{\\text{R}}_{\\text{2}}\\text{+}{{\\text{R}}_{\\text{2}}}^{\\text{2}}\\right)}{\\text{45}\\left({\\text{R}}_{\\text{1}}\\text{+}{\\text{R}}_{\\text{2}}\\right)\\text{v}}\\text{ }\\text{ }\\text{ (1-2)}$$\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere \u003cem\u003eQ\u003c/em\u003e refers to the heat input to the workpiece, \u003cem\u003ev\u003c/em\u003e is the welded speed, \u003cem\u003eR\u003c/em\u003e1 and \u003cem\u003eR\u003c/em\u003e2 denote the shoulder radius of the stirring needle and the stirring needle radius, respectively. \u003cem\u003en\u003c/em\u003e indicates the rotational speed of the stirring needle, \u003cem\u003eP\u003c/em\u003e represents the welding pressure, and \u003cem\u003e\u0026micro;\u003c/em\u003e is the friction coefficient. Eq.\u0026nbsp;(1\u0026ndash;2) demonstrates that the frictional heat \u003cem\u003eQ\u003c/em\u003e generated by the workpiece depends on rotational speed n and welded speeds \u003cem\u003ev\u003c/em\u003e. Furthermore, these parameters, along with a certain amount of downward pressure, affect the axial force \u003cem\u003eP\u003c/em\u003e exerted on the workpiece. The axial force, in turn, influences the subsequent heat of deformation and ultimately the weld head quality. The process parameters examined in this research paper comprise the rotational and welded speeds, whereas the other parameters remained constant. The heat input \u003cem\u003eQ\u003c/em\u003e is determined by the ratio of rotational speed to welded speed, that is, \u003cem\u003eQ\u003c/em\u003e is directly proportional to the value of \u003cem\u003en\u003c/em\u003e/\u003cem\u003ev\u003c/em\u003e. Comparison of heat inputs across different data sets, as depicted in the line graph in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, revealed that for a given welded speed, an increase in rotational speed led to increased heat input and grain size. Moreover, the amount of wear increased compared with the results displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(f). However, W8 exhibited a considerable decrease in wear, followed by the increased wear of W9. Zhang et al.[\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e] mentioned that heat input also affects grain size, with excessive input leading to large grains and insufficient input resulting in weld defects. The heat inputs for specimens W1, W4, W7, W8, and W9 were 16, 14, 12.5, 15, and 17.5 (J/mm), respectively. Figures\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(d) and 4(f) provide supporting evidence showing the similarities of the coefficients of friction and wear rates of W1 and W8. This finding further substantiates the importance of a heat input of approximately 16 J/mm (blue dashed line and red triangle in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e shows the internal microstructure after friction stirred processing. It is well known that nano-twinning exists in materials with low level of dislocation energy[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e], and 7075 aluminum alloy belongs to the materials with high level of dislocation energy, which is not conducive to the formation of nano-twinning. However, after friction stir processing, the dislocations are accumulated due to the intense plastic deformation, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(a)-(c). Moreover, the higher rotational speed makes 7075 aluminum alloy less prone to dislocation migration, so that the twin structure appears internally after stirring and friction processing, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(d). The experimental results of the plastic nano twin structures are in good accordance with those findings based on XRD. The Fourier transform (FFT) of the grain organization in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(e) yields a grain spacing of 0.83 nm and 0.44 nm, respectively. In addition, the HRTEM image shows an atomic-scale twin structure with a twin size of about 3.33 nm, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(h) and (i). Generally, it is difficulty to form twins in Al alloy microstructure because it belongs to FCC metals with high stacking fault energy (86 mJ/m2)[\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. Owing to the high strain rate induced by FSP, the dislocation movement velocity is fast, resulting in dislocation accumulation, which is more prone to the nucleation of deformation twins. The presence of twin crystals not only improves the toughness of the weld after friction stirred processing, but also reduces the fatigue damage of the material. In addition, since the twin crystals can lead to the stress distribution on the material surface to become more uniform[\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e], the material will be able to reduce the crack expansion rate during the reciprocating motion. Liu and his co-workers[\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]revealed that the enhanced wear resistance performance of NiCoFeCrMoW were also due to the existence of a large number of deformation twins. Simultaneously, Chen et al.[\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e] proposed a promising approach to introduce twins in ceramic films and enhance the wear resistance performance of the Si matrix.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe friction and wear characteristics and mechanism of various FSP parameters were analyzed via XRD, SEM technology, etc. The primary findings of this research are summarized as follows:\u003c/p\u003e\n\u003cp\u003e(1) Grains were refined after FSP treatment compared with the BM. However, the process parameters directly affected the microstructure. Especially, W8 exhibited better welded and rotation speeds (80 and 1200 rpm, respectively) than W2 (60 and 1200) and the smaller and more uniform distribution of grains in the weld zone. And the microstructure was accompanied by the generation of a large number of highly plastic nano twin structures.\u003c/p\u003e\n\u003cp\u003e(2) After FSP, the wear resistance of specimens was improved, and the average coefficient of friction in the stabilization phase of W1 and W8 increased by 19% and 13%, respectively, compared with those of the BM. The wear rates of W1 and W8 increased by 45% and 40%, respectively, compared with that of the BM. The wear mechanisms were abrasive and adhesive wear. And the formation of nano twin structure greatly enhances the adhesive wear resistance of FSPed specimens.\u003c/p\u003e\n\u003cp\u003e(3) Rotational speed is directly proportional to heat input, and wear resistance with heat input showed a trend opposite that of grain size, which is the main factor affecting the wear resistance of FSPed specimens. Thus, after evaluation of the combined properties and welding efficiency, the optimal process parameter was determined to be a rotational speed of 1000\u0026thinsp;\u0026minus;\u0026thinsp;200 rpm at a certain welding speed, which can provide an optimized heat input of 15\u0026ndash;16 J/mm.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors are grateful for the support provided by the Natural Science Major Foundation of the Jiangsu Higher Education Institutions (Grant No.19KJA460003), the National Natural Science Foundation of China (Grant No.52205157).\u003c/p\u003e\n\u003cp\u003e☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;☐ The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMirjavadi SS, Alipour M, Hamouda AMS et al (2017) Effect of multi-pass friction stir processing on the microstructure, mechanical and wear properties of AA5083/ZrO2 nanocomposites[J]. J Alloy Compd 726:1262\u0026ndash;1273\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMoustafa EB, Mosleh AO (2020) Effect of (Ti\u0026ndash;B) modifier elements and FSP on 5052 aluminum alloy[J]. J Alloy Compd 823:153745\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeng W, Gao Y, Li H et al (2024) Effects of different initial states on dynamic tensile properties and microstructure of 7075 aluminum alloy[J]. Mater Sci Eng A 891:145939\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMabuwa S, Msomi V, Ndube-Tsolekile N et al (2022) Status and progress on fabricating automotive-based aluminium metal matrix composites using FSP technique[J]. Materials Today: Proceedings, 56: 1648\u0026ndash;1652\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi S, Paidar M, Liu S et al (2022) Importance of pin number on mechanical properties and wear performance during manufacturing of AA6061/316 surface composite via FSP[J]. Mater Lett 326:132919\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu R, Li Y, Sun Y et al (2023) Microstructure and properties of FeCoNiCrAl high-entropy alloy particle-reinforced Cu-matrix composites prepared via FSP[J]. J Alloy Compd 940:168906\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNabi S, Rathee S, Srivastava M (2024) Friction and wear analysis of Al-5052/NiTi surface composites fabricated via friction stir processing[J]. Tribol Int 191:109179\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu T, Zhang W, Wu SD et al (2003) Equal channel angular pressing of atwo-phase alloy Mg-8Li-1 Al II. deformation modes during ECAP[J]. Acta Metall Sin. (08):790\u0026ndash;794\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBagheri B, Abbasi M, Abdollahzadeh A et al (2020) Effect of second-phase particle size and presence of vibration on AZ91/SiC surface composite layer produced by FSP[J]. T Nonferr Metal Soc 30(4):905\u0026ndash;916\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang JG, Dong G (2018) Fundamentals of tribology[M]. Xi'an University of Electronic Science and Technology, Xi'an\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang HJ, Sun SL, Liu HJ et al (2020) Characteristic and mechanism of nugget performance evolution with rotation speed for high-rotation-speed friction stir welded 6061 aluminum alloy[J]. J Manuf Process 60:544\u0026ndash;552\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShivaKumar GN, Rajamurugan G (2023) Significance of FSW process parameters and tialite particle reinforcement at the weld zone of AA6082 alloy[J]. Mater Lett 353:135289\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang L, Wei C, Jiang F et al (2024) Significant reduction in friction and wear of an ultrafine-grained single-phase FeCoNi alloy through the formation of nanolaminated structure[J]. 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Philosophical Magazine: J Theoretical Experimental Appl Phys 35(5):1161\u0026ndash;1172\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShao YF, Cao R, Liu YL (2023) Molecular dynamics study on the uniaxial tensile behavior of mono-layer MoTe2 film defected by mirror twin boundary[J]. Comp Mater Sci 230:112481\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu X, Wu Y, Wang Y et al (2022) Enhanced dynamic deformability and strengthening effect via twinning and microbanding in high density NiCoFeCrMoW high-entropy alloys[J]. J Mater Sci Technol 127:164\u0026ndash;176\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen Y, Yan X, Guo T et al (2023) Cross-interface growth mechanism of nanotwins in extremely high stacking-fault energy ceramic layer[J]. Acta Mater 257:119189\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Wear resistance, process parameters, FSP, 7075 aluminum alloy","lastPublishedDoi":"10.21203/rs.3.rs-4258326/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4258326/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work investigated effects of friction stirred processing (FSP) parameters on the wear resistance of 7075 aluminum alloy. The results indicate the significantly higher wear rate and average coefficient of friction during the stabilization stage of samples W1 (welding speed: 60 mm/min; rotation speed: 1000 rpm) and W8 (welding speed: 80 mm/min; rotation speed: 1200 rpm), with increases of 45% and 40% for the wear rate, respectively, and 19% and 13% for coefficient of friction in comparison with the untreated material. The optimized FSP parameters can considerably improve the wear resistance of the material by affecting the heat input, which altered the grain size and distribution in the welded zone. X-Ray diffraction and scanning electron microscopy/energy dispersive spectroscopy studies provided the mechanism underlying grain size and plastic nano twin structures contributions to wear resistance.\u003c/p\u003e","manuscriptTitle":"Influence of process parameters on wear resistance of surfaces modified by friction stirring processing in 7075 aluminum alloy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-03 14:29:28","doi":"10.21203/rs.3.rs-4258326/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-06-04T06:36:52+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-17T07:13:20+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Welding in the World","date":"2024-04-18T04:46:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-17T03:00:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Welding in the World","date":"2024-04-15T09:51:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"welding-in-the-world","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"witw","sideBox":"Learn more about [Welding in the World](https://www.springer.com/journal/40194)","snPcode":"40194","submissionUrl":"https://www.editorialmanager.com/witw/","title":"Welding in the World","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"44b5a810-5254-439b-b601-1bf7bd1f3332","owner":[],"postedDate":"June 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-06-03T14:29:28+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-03 14:29:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4258326","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4258326","identity":"rs-4258326","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}