Effect of post-weld heat treatment on AA6351 friction stir welds

Effect of post-weld heat treatment on AA6351 friction stir welds | 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 Effect of post-weld heat treatment on AA6351 friction stir welds RAGHAVA RAO MADDA, Lakshmi Saranya B, Siva Prasad G, Venkata Rao Ch, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4208352/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Al-Mg-Si (6xxx) alloys have superior properties to other aluminium alloys, making them suitable for aerospace and defence applications. However, their weldments are susceptible to various issues that affect their microstructural changes, mechanical properties, and corrosion resistance. The use of friction stir welding has been proven to be an effective solution for these problems, and this study aimed to investigate the microstructural changes, mechanical properties, and pitting potential (Epit) of AA6351 alloy friction stir welds. The present study used AA6351 with a thickness of 6mm alloy plates for welding and characterized the welds' microstructure, pitting corrosion resistance, and mechanical properties of hardness and tensile strength. Post-weld heat treatment (PWHT) for solutionizing at 523°C for 0.5hrs followed by 8 hrs at 177⁰C (STA-solutionizing treatment with ageing) was applied to improve the welds' corrosion resistance and mechanical properties. A comparison between the base metal and weldment before and after PWHT showed that the ageing treatment of the welds improved their mechanical properties and pitting corrosion resistance. This treatment caused re-precipitation and redistribution of precipitates in the welds’ grain-refined stir zone, restoring their mechanical properties and pitting corrosion resistance. Therefore, this study established that post-weld solutionizing at 523°C for 0.5 hrs and then ageing at 177⁰C for 8hrs can restore the overall mechanical and pitting corrosion behaviour of AA6351 alloy friction stir welds. FSW AA6351 PWHT SEM Mechanical properties Pitting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction AA6351 is an aluminum alloy that has been developed as a high-strength material with good corrosion resistance. This alloy contains silicon, magnesium, and manganese as its main alloying elements, and often used in applications where high strength and good corrosion resistance are required, such as in the construction of aircraft and aerospace components, marine applications as structural components [ 1 – 4 ]. One of the significant advantages of AA6351 alloy is its excellent machinability, which makes it easier to fabricate and form into various shapes and sizes. It also has good weldability, which allows to create complex structures and components. Furthermore, it can undergo heat treatment as AA6351 is heat treatable. Through the precipitation hardening phenomenon, it would get strengthened and hardened by heating it to a particular temperature, and then quenched to produce a supersaturated solid solution [ 5 – 6 ]. This is followed by aging at a lower temperature to allow the formation of fine precipitates that strengthen the material [ 7 ]. Even though AA6351 is typically regarded to have acceptable weldability, if appropriate welding methods are not followed, It is susceptible to porosity, shrinkage, and hot cracking. Hot cracking may result from the high magnesium content, particularly during welding of thick sections or applying higher heat inputs. By utilizing filler alloys (decreased magnesium content), applying appropriate preheating, post-weld heat treatment (PWHT), hot cracking and porosity risks can be minimized. Friction stir welding (FSW) is a solid-state welding which has several advantages over fusion welding techniques, including fewer weld flaws, minimal distortion, good quality, and lower residual stresses. The axial force, tool pin profile, welding speed, and rotational speed are some of the welding parameters that affect the mechanical characteristics of the friction stir joints [ 8 ]. By exerting prominent effect on temperature distribution and material flow pattern, these parameters influence the microstructural evolution of a material [ 9 ]. According to Pramod Kumar et al. mechanical characteristics of AA6351 FS welds with regard to microstructure, UTS of the weldments are greater than parent base metal [ 10 ]. Palanivel et al. examined the microstructure and mechanical characterization of the AA5083-H111 and AA6351-T6 FS weldments [ 11 ]. G.Gopala Krishna et al., stated that AA6351 FSW similar welds had better mechanical properties than AA6351-AA5083 dissimilar welds [ 12 ]. Akinlabi et al. investigated the influence of traverse welding speed on dissimilar FSW of copper (C11000) and aluminum (Al 5754) sheets and observed that when welding speed increased, the weldments' average ultimate tensile strength declined. And also, Intermetallic compounds presence was identified in the weldment [ 13 ]. In a T-joint design, Zhao et al. studied the FSW of Al 6013-T4 at various welding process parameters. They analyzed that the weldment quality was greatly affected by imperfections with varied welding parameters [ 14 ]. AA5083-AA6082 joints was examined by Peel et al., who discovered that the tool's rotating speed had a greater impact on heat generation during welding compared to traverse speed [ 15 ]. Steuwer et al. investigated the effect of traverse speed, tool rotation on residual stress of dissimilar weld joint (AA5083-AA6082). In order to optimize residual stress, they came to the conclusion that tool rotational speed was a significant process variable. [ 16 ]. Leitao et al. found that the precipitate distribution and grain size in the TMAZ affected the AA5182-AA6016 joints tensile behaviour [ 17 ]. Leitao et al. used deep drawing cylindrical cups to analyze the formability of AA5182-H111 and AA6016-T4 joints, and discovered that formability limitations were controlled by mismatch in mechanical characteristics of weldment and base materials [ 18 ]. The microstructural and mechanical properties of the FSW joints of the aluminum alloys AA6101-T6 and AA6351-T6 were investigated by Toppo et al. They found that the total weight percentage of Si decreases with increasing tool speed, leading to the precipitation of finer Mg2Si and a subsequent loss in strength upon the appearance of fibrous fractures [ 19 ]. M. Karthikeyan et al., reported that FS welds of AA6061 contain enhanced strength as a weld joint compared to parent material and mechanical properties substantially improved during Post Weld Heat Treatment (PWHT) [ 20 ].Literature study clearly suggests that post weld heat treatments are advantageous to the weld joints as it enhances the mechanical and corrosion resistance of the weldment [ 21 ]. But very scarce research has been available on the corrosion resistance and mechanical property correlation with respect to microstructural correlation after PWHT of FS weldment which is hassle and defect free compared to conventional welding techniques [ 22 ]. Given the foregoing, the current study aims to investigate the effect of PWHT on the mechanical and pitting corrosion behavior of AA6351 FS welds in response to microstructural changes. 2. Experimental Procedure The chemical constituents of AA6351 alloy (wt %)) is given below. AA6351 alloy plates of thickness 6 mm are friction stir welded using the conical-shaped tool (shoulder dia-20mm, Pin dia.-6mm (base) to 3mm (tip) with pin length of 5.7mm, Fig. 1 ). The plates were welded (butt) length wise, using a 3-axis semi- automated milling machine. Table 2.1 Chemical composition of AA6351 Al alloy (Wt %) Si Mg Mn Fe Cu Zn Cr Ti Al 0.929 0.642 0.726 0.072 0.025 0.002 0.002 0.20 97.4 During the post-weld heat treatment process, the samples are heated at 523°C for an 0.5 hour in a muffle furnace, followed by water quenching and then ageing in an oven at 177°C for 8 hours. A microstructural analysis of the Nugget zone (NZ), heat-affected zone (HAZ), and base metal of the weldment was conducted using optical microscopy (Olympus- BX53MRF) and SEM(scanning electron microscopy) with EDS (energy dispersive spectroscopy) (Model: JEOL JSM-IT500). Each and every figure included information about the voltage, detectors and working distance operated during SEM imaging. For in-depth chemical analysis, XRD (X-ray diffraction)-Rigaku manufacture, Miniflex 600 was utilized. The sample was prepared in accordance with ASTM E3 standard- scratch free, but without etching. According to ASTM E8 standard, tensile tests with extensometers were performed on base metal, FS, and PWH treated welds using UTM, Instron make-8801 at a constant strain rate-0.1 mm/sec. According to ASTM E384 standard, Micro-vickers hardness testing equipment, Model: Economet VH-1MDX was used to perform hardness testing with a 500g load. The tester had a dwell duration of 15 seconds and a total of 48 readings. The electrochemical system (Gill-AC) was utilized to investigate the weld sample’s pitting corrosion behavior, using a carbon electrode-auxiliary electrode, SCE-reference electrode. The testings were conducted in a 3.5% NaCl solution that was aerated, and the pH was adjusted to 10 by adding KOH. 3. Results and discussions Microstructural studies: The optical microstructures of AA6351 base metal in FS welded and PWH-treated conditions are depicted in Fig. 2 . The microstructure shows longitudinally elongated grains of α-Al matrix in dark color and a secondary phase in light color, which are present in both conditions. However, Fig. 2 b shows a higher concentration of the light-colored secondary phase, which is likely due to the influence of solutionizing followed by ageing during PWHT. The macrostructures of FS weld and PWH treated sample shown, defect free weld joint with clearly distinguished various zones in weldment (Fig. 3 a, 3 b). From this macroscopic analysis, FS welded sample shown well-defined wavy interface between stir zone and TMAZ. Whereas PWH treated sample shown more homogenized macrostructure with vague zonal distribution. From Fig. 3 a, HAZ (as welded) exhibits a grain structure with coarse columnar grains, while the PWH-treated sample displays a microstructure with a finer grain size with uniformly distributed secondary phase and distinct features. The phase (secondary phase) which appears in dark color in PWH-treated microstructures is more likely to be Mg 2 Si, whereas the minute presence of this phase can be observed from the FS welded microstructures [ 23 – 25 ] (Fig. 4 ). It may be due to partial dissolution of precipitation during welding. Due to their high stacking fault energy, aluminium alloys tend to form dense dislocation walls and dislocation tangles during deformation [ 26 ]. These structures can then develop into partial boundaries of misorientation, which ultimately become sub-grain boundaries and result in grain refinement. As stir zone experiences severe plastic deformation while FS welding, the finer grain size can be observed in the stir zone of as welded and PWH treated conditions. In the TMAZ also, PWHT sample displays stress-free fine grains may due to solutionizing and ageing compared to FS-welded samples. The SEM microstructures of the stir zone shown uniformity in size, distribution and increased volume fraction of secondary phase (predominantly Mg 2 Si, from Fig. 4 ) in PWHT condition compared to FS weld condition. The partial dissolution of precipitates and fragmentation to the extent of negligable due to severe plastic deformation may resulted in the low no. of precipitates in FS welded condition. The elemental mapping of the stir zone shows an uneven phase distribution and elemental free zones in the microstructure of the weld sample. In contrast, there are no element-free zones in the PWH treated sample, which exhibits a consistent distribution of elements throughout the PWHT condition microstructure. This indicates that the PWH treated sample had a higher precipitation density than the weld sample. The X-ray diffraction analysis of FS weldment and PWH-treated sample shown distinguished peaks of Al (aluminium) which is major constiuent of the alloy. Additionally the presence of Mg 2 Si was identified according to JCPDS database, as seen in Fig. 5 . From comparing the Fig. 5 a and 5 b, the peaks of Mg 2 Si and Al evidently shows that substantial crystallographic adjustment during PWHT due to microstrucutre homogenization. The broadened yet distinct peak of Mg 2 Si in Fig. 5 b compared to FS welded sample may indicates the slight coarsening of precipitates during PWHT which are partially dissolved or, in negligable size. These microstructural variations often aids a significant modification in the properties of a weldment with more homogeneity, without attenuation of efficiency. These research findings helps in extending our understanding of the possible microstructural changes during FS welding in terms of size, composition and volume fraction. Mechanical properties : a) Tensile studies: Table 3.1. Tensile Properties of AA6351 FS Welds before and after PWHT Weld Yield strength (MPa) Tensile Strength (MPa) % Elongation Fracture Zone As weld 143.32 162.318 13.0000 HAZ PWHT (STA) 177.754 198.391 10.6000 HAZ Table 3.1 shows the yield strength, tensile strength and % of elongation of FS welded and PWHT samples to analyze the tensile properties. In comparison to the weld sample, the PWH-treated sample demonstrates significantly improved tensile characteristics from the above data. According to the tensile values, the typical precipitation hardening phenomena was observed with an increase in the tensile strength of the PWHT sample. Though grain refinement supports the strength of FS weld sample due to formation of sub-grain boundaries, the amount of mechanical stresses generated during severe plastic deformation are detrimental to the mechanical behavior of FS welded sample. The dislocation tangles generated during welding can acts as initiating sites for micro cracks which have adverse effect on tensile behaviour of FS weld sample [27]. The partial dissolution of precipitates during FS welding, due to heat generation and fragmentation of precipitates due to severe deformation may contribute to the lower tensile properties of the FS weld sample in comparison to the PWH treated sample. The increase in the amount of precipitation during PWHT could be the reason for the reduction in elongation percentage, as these two factors are interconnected. And also stress relieving during PWHT and absence of PFZs which are formed due to dissolution of precipitates may responsible for better tensile strength value of PWHT sample [28]. Heat cycles during welding can cause HAZ to vary in grain morphology in both the welded and PWH treated states compared to base metal and stir zone. And the fracture position at HAZ clearly supports the above. 60% of the FS welded sample's fracture surface is dimpled, while 40% is intergranular. In contrast, the PWHT sample exhibits 20% of dimple fracture and approximately 80% of intergranular fracture with fine grain structure. The formation of voids can be observed in FS weld sample, which can be nucleated at matrix and particle interface. The dislocation pile-up at grain boundaries by combining with localized stresses generated during FS welding may lead to the formation of voids as a consequence of de-cohesion. More fish eye (starting point of fracture) like structures are observed in FS welded condition in larger size compared to PWH treated condition. The coarser grain size was observed in FS weld sample with more ductile failure with dimpled structures. The homogenized microstructure with relieved stresses during PWHT are may be the reason for inter-granular failure of PWHT sample with very small fraction of micro voids. b) Hardness studies: Table 3.2. Micro Vickers hardness values of AA6351, before and after PWHT JOINT/WELD HARDNESS VALUES ( in HV) BM AHAZ ATMAZ SZ RTMAZ RHAZ FSW-AW 50.12 61.5 68 67.5 62.7 61.5 FSW-STA 60 81.22 84.58 86.38 83 80.38 By comparing the hardness values of base metal, FS weld and PWH treated samples, PWH treated sample shows better hardness (Table 3.2). less gradient was observed in the hardness values of various zones of PWH treated weldment. The uniform distribution of precipitates and their increased volume fraction due to reprecipitation may attributed to the enhanced hardness values of PWH treated sample than FS weld sample. The relationship between fine grain size and increased hardness suggests that grain size and no. of precipitates have a significant impact on the hardness increase. The HAZ which contains coarser grain size evidently shown lower hardness when compared to remaining zones. The modified texture in the TMAZ may contribute to the increase in hardness, with the retreating side TMAZ exhibiting lower hardness than the advancing side. This variation in hardness can be ascribed to the longer heat residing time due to material deposition at the retreating side, leading to coarser grain size. Corrosion studies: Table 3.3. Pitting potential (E pit ) values of AA6351, before and after PWHT JOINT/WELD Pitting potential (E pit ) ( in mV) BM AHAZ ATMAZ SZ RTMAZ RHAZ AW -684 -653 -637 -601 -667 -650 PWHT(STA) -618 -590 -551 -534 -565 -598 From the Fig 11, The E pit values shows overall better corrosion resistance values in PWH treated sample, compared to FS weld sample. Fig 11.b depicts the E pit value of -534mV at stir zone, which has higher corrosion resistance among all the other zone. It can be attributed to the coherent reprecipitation and their uniform distribution [29-30]. In addition, the stir zone curve showed a greater degree of passivity in comparison to both the post weld and FS weld samples. The presence of more number of precipitates, which serve as a barrier to inhibit corrosion attack, is responsible for the increased passivity that was observed from the stir zone curve. The coherency of these precipitates also significantly contributes to the improved corrosion resistance of stir zone curve. The better corrosion resistance observed in both the advancing and retreating side TMAZ in PWHT condition may be attributed to reduced sensitivity caused by residual stresses generated during the FS welding process. The lower corrosion resistance observed in the FS-weld HAZ, as compared to the FS-weld SZ, TMAZ, and PWHT samples, may be due to the coarsening of existing precipitates and their non-uniform distribution [31-33]. The enhanced corrosion resistance observed after solutionizing and ageing (STA) may be attributed to the replacement of severely deformed grains with stress-free recrystallized grains. In FS welded condition, the dislocation tangles generated during FSW can act as potential corrosion initiation sites with their higher energy. In the as-welded sample, the presence of precipitate free zones (PFZs), which are formed as a result of frictional heat generated during FS welding, promotes corrosion due to galvanic coupling with the α-Al solid solution matrix. Additionally, preferential grain boundary corrosion is a potential factor to the lower corrosion resistance that has been observed from FS-welded sample. The homogeneity achieved across the microstructure through PWHT process has a substantial impact in strengthening the weldment resistance to corrosion compared to the FS-welded sample. 4. Conclusions The microstructure, mechanical characteristics, and pitting corrosion behavior of AA6351 (FS weld) and PWH treated state were compared in the present study. The key findings of the current study are as follows: The microstructure of the FS welded condition exhibits the dissolution of finer precipitates and partial dissolution of secondary phases, resulting in the formation of PFZs. In contrast, the PWH treated sample shows a homogenous microstructure with uniform reprecipitation due to the solutionizing along with ageing processes. The PWH-treated sample has shown surpassing mechanical properties compared to the FS welded sample, due to their uniform distribution and increased volume fraction of precipitation throughout the microstructure. This has played a significant role in improving the properties, resulting in better mechanical behavior, including yield and tensile strength. The lower pitting corrosion resistance observed in the FS-welded sample may be due to galvanic coupling, while the PWH-treated sample exhibits better pitting corrosion resistance due to the presence of coherent precipitates. The overall properties of mechanical and pitting corrosion behaviour of PWH treated FS weld joint shows better results compared to FS weld joint, with less gradient in hardness values, enhanced strength in tensile values, and higher pitting corrosion resistance. These benefits can be attributed to the fact that the weld joint attained homogeneous chemistry and microstructure through PWHT. Declarations The authors have no relevant financial or non-financial interests to disclose. The authors have no conflicts of interest to declare that are relevant to the content of this article References N. Yuvaraj, V. Mohanavel, M. Ravichandran, B. N. Sreeharan, en T. 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Investigations on the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 alloy. Int J Fatigue 2008; 30: 1543-1555. Cite Share Download PDF Status: Posted Version 1 posted 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-4208352","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":288346333,"identity":"2fc31aba-4fbb-4e59-a367-131d110599f6","order_by":0,"name":"RAGHAVA RAO MADDA","email":"data:image/png;base64,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","orcid":"https://orcid.org/0009-0009-2166-5558","institution":"Andhra University College of Engineering","correspondingAuthor":true,"prefix":"","firstName":"RAGHAVA","middleName":"RAO","lastName":"MADDA","suffix":""},{"id":288346334,"identity":"6440bcd7-ae81-47c3-87c5-2e90a8c0cd69","order_by":1,"name":"Lakshmi Saranya B","email":"","orcid":"","institution":"Andhra University College of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Lakshmi","middleName":"Saranya","lastName":"B","suffix":""},{"id":288346335,"identity":"1fe3bcc4-6a54-4993-95ff-3702c9b496bd","order_by":2,"name":"Siva Prasad G","email":"","orcid":"","institution":"Andhra University College of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Siva","middleName":"Prasad","lastName":"G","suffix":""},{"id":288346336,"identity":"abf13930-aaea-4eb3-8f1c-4668cf842db0","order_by":3,"name":"Venkata Rao Ch","email":"","orcid":"","institution":"Andhra University College of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Venkata","middleName":"Rao","lastName":"Ch","suffix":""},{"id":288346337,"identity":"1d85837c-9aba-4fbd-82c7-67745b4a2b4b","order_by":4,"name":"Srinivasa Rao K","email":"","orcid":"","institution":"Andhra University College of Engineering","correspondingAuthor":false,"prefix":"","firstName":"Srinivasa","middleName":"Rao","lastName":"K","suffix":""}],"badges":[],"createdAt":"2024-04-02 18:08:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4208352/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4208352/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54404724,"identity":"13c4effc-c69f-4b75-aade-e7549267e073","added_by":"auto","created_at":"2024-04-10 03:27:45","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":123310,"visible":true,"origin":"","legend":"\u003cp\u003ea) During FSW b) Tool used for FSW\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/6b443d9eea88d48db682d133.jpg"},{"id":54404725,"identity":"d9e0ecc8-9646-43b2-96ab-b2bd2cf67c73","added_by":"auto","created_at":"2024-04-10 03:27:45","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":554899,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microstructure of AA6351 base metal a) FS welded b) PWH treated\u003c/p\u003e","description":"","filename":"floatimage2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/15d5ad53c4e5a6e570caa825.jpg"},{"id":54404728,"identity":"21362c51-4f04-4d2f-9944-f29e32e1a8c7","added_by":"auto","created_at":"2024-04-10 03:27:45","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":4121268,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microstructures of AA6351 a) As weld condition \u0026nbsp;b) Post-weld heat treated condition\u003c/p\u003e","description":"","filename":"floatimage3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/3b5221d27dec8986abbabe0f.jpg"},{"id":54405103,"identity":"e7b5ad32-44b0-4235-baa0-f935d8879f3e","added_by":"auto","created_at":"2024-04-10 03:35:45","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":375617,"visible":true,"origin":"","legend":"\u003cp\u003eSEM microstructure of AA6351 FS weld, Stir zone a) FS welded b) PWH treated\u003c/p\u003e","description":"","filename":"floatimage4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/0279e5b81c9bba16e66780ef.jpg"},{"id":54405104,"identity":"8d812710-1092-4ed4-a6ff-47d941a12be9","added_by":"auto","created_at":"2024-04-10 03:35:45","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":149964,"visible":true,"origin":"","legend":"\u003cp\u003eXRD analysis of AA6351 FS weld a) FS welded b) PWH treated\u003c/p\u003e","description":"","filename":"floatimage5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/4cb9b2279f4160db8f67d583.jpg"},{"id":54404730,"identity":"df50637b-6d20-4eb3-9d9f-2a956e6d5074","added_by":"auto","created_at":"2024-04-10 03:27:45","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":247265,"visible":true,"origin":"","legend":"\u003cp\u003eElemental mapping of AA6351 FS nugget zone in FS weld condition\u003c/p\u003e\n\u003cp\u003ea)Ref.image b) Mg c) Mn d) Si e) Al\u003c/p\u003e","description":"","filename":"floatimage6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/62cf6e1b0825395a8931b7e1.jpg"},{"id":54404733,"identity":"c7384ce6-2560-4041-8d6c-848983ea865c","added_by":"auto","created_at":"2024-04-10 03:27:46","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":381693,"visible":true,"origin":"","legend":"\u003cp\u003eElemental mapping of AA6351 FS nugget zone in PWH treated condition\u003c/p\u003e\n\u003cp\u003ea)Ref.image b) Mg c) Mn d) Si e) Al\u003c/p\u003e","description":"","filename":"floatimage7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/5cbe4985697dd1d59bb7e351.jpg"},{"id":54405105,"identity":"0040a464-7f8e-40ca-a71a-917e7e551dbb","added_by":"auto","created_at":"2024-04-10 03:35:45","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":139433,"visible":true,"origin":"","legend":"\u003cp\u003eTensile graphs of AA6351 FS weld and PWHT samples\u003c/p\u003e","description":"","filename":"floatimage8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/dd571ba513d4e1f2fa866b9f.jpg"},{"id":54404726,"identity":"804e7c6c-61e3-4b4c-be6f-114fd77dcae1","added_by":"auto","created_at":"2024-04-10 03:27:45","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":432723,"visible":true,"origin":"","legend":"\u003cp\u003eFracture surface of AA6351 FS weld a) as weld b) PWHT\u003c/p\u003e","description":"","filename":"floatimage9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/88ef361dab6eb6d0e6fdc438.jpg"},{"id":54405106,"identity":"73135a6e-367a-423c-b31c-50008820880d","added_by":"auto","created_at":"2024-04-10 03:35:45","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":407170,"visible":true,"origin":"","legend":"\u003cp\u003eMicro Vickers hardness graph of AA6351 FS welds, before and after PWHT\u003c/p\u003e","description":"","filename":"floatimage10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/e2c68dbda60696578e38693b.jpg"},{"id":54404734,"identity":"4d4a9d8c-e8cb-4da0-9c1e-f32a8b554ae9","added_by":"auto","created_at":"2024-04-10 03:27:46","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":800756,"visible":true,"origin":"","legend":"\u003cp\u003ePotentio-dynamic polarization curve of AA6351 FS Welds\u003c/p\u003e","description":"","filename":"floatimage11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/297b14558bd9bcd473d346a2.jpg"},{"id":57590257,"identity":"37d78d09-b0d9-4030-a88f-8065766401bb","added_by":"auto","created_at":"2024-06-03 04:47:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8075053,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4208352/v1/3eaa7be5-2676-4194-a581-a727970478fa.pdf"}],"financialInterests":"","formattedTitle":"Effect of post-weld heat treatment on AA6351 friction stir welds","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAA6351 is an aluminum alloy that has been developed as a high-strength material with good corrosion resistance. This alloy contains silicon, magnesium, and manganese as its main alloying elements, and often used in applications where high strength and good corrosion resistance are required, such as in the construction of aircraft and aerospace components, marine applications as structural components [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. One of the significant advantages of AA6351 alloy is its excellent machinability, which makes it easier to fabricate and form into various shapes and sizes. It also has good weldability, which allows to create complex structures and components. Furthermore, it can undergo heat treatment as AA6351 is heat treatable. Through the precipitation hardening phenomenon, it would get strengthened and hardened by heating it to a particular temperature, and then quenched to produce a supersaturated solid solution [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This is followed by aging at a lower temperature to allow the formation of fine precipitates that strengthen the material [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Even though AA6351 is typically regarded to have acceptable weldability, if appropriate welding methods are not followed, It is susceptible to porosity, shrinkage, and hot cracking. Hot cracking may result from the high magnesium content, particularly during welding of thick sections or applying higher heat inputs. By utilizing filler alloys (decreased magnesium content), applying appropriate preheating, post-weld heat treatment (PWHT), hot cracking and porosity risks can be minimized. Friction stir welding (FSW) is a solid-state welding which has several advantages over fusion welding techniques, including fewer weld flaws, minimal distortion, good quality, and lower residual stresses. The axial force, tool pin profile, welding speed, and rotational speed are some of the welding parameters that affect the mechanical characteristics of the friction stir joints [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. By exerting prominent effect on temperature distribution and material flow pattern, these parameters influence the microstructural evolution of a material [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. According to Pramod Kumar et al. mechanical characteristics of AA6351 FS welds with regard to microstructure, UTS of the weldments are greater than parent base metal [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Palanivel et al. examined the microstructure and mechanical characterization of the AA5083-H111 and AA6351-T6 FS weldments [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. G.Gopala Krishna et al., stated that AA6351 FSW similar welds had better mechanical properties than AA6351-AA5083 dissimilar welds [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Akinlabi et al. investigated the influence of traverse welding speed on dissimilar FSW of copper (C11000) and aluminum (Al 5754) sheets and observed that when welding speed increased, the weldments' average ultimate tensile strength declined. And also, Intermetallic compounds presence was identified in the weldment [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In a T-joint design, Zhao et al. studied the FSW of Al 6013-T4 at various welding process parameters. They analyzed that the weldment quality was greatly affected by imperfections with varied welding parameters [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. AA5083-AA6082 joints was examined by Peel et al., who discovered that the tool's rotating speed had a greater impact on heat generation during welding compared to traverse speed [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Steuwer et al. investigated the effect of traverse speed, tool rotation on residual stress of dissimilar weld joint (AA5083-AA6082). In order to optimize residual stress, they came to the conclusion that tool rotational speed was a significant process variable. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Leitao et al. found that the precipitate distribution and grain size in the TMAZ affected the AA5182-AA6016 joints tensile behaviour [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Leitao et al. used deep drawing cylindrical cups to analyze the formability of AA5182-H111 and AA6016-T4 joints, and discovered that formability limitations were controlled by mismatch in mechanical characteristics of weldment and base materials [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The microstructural and mechanical properties of the FSW joints of the aluminum alloys AA6101-T6 and AA6351-T6 were investigated by Toppo et al. They found that the total weight percentage of Si decreases with increasing tool speed, leading to the precipitation of finer Mg2Si and a subsequent loss in strength upon the appearance of fibrous fractures [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. M. Karthikeyan et al., reported that FS welds of AA6061 contain enhanced strength as a weld joint compared to parent material and mechanical properties substantially improved during Post Weld Heat Treatment (PWHT) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].Literature study clearly suggests that post weld heat treatments are advantageous to the weld joints as it enhances the mechanical and corrosion resistance of the weldment [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. But very scarce research has been available on the corrosion resistance and mechanical property correlation with respect to microstructural correlation after PWHT of FS weldment which is hassle and defect free compared to conventional welding techniques [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Given the foregoing, the current study aims to investigate the effect of PWHT on the mechanical and pitting corrosion behavior of AA6351 FS welds in response to microstructural changes.\u003c/p\u003e"},{"header":"2. Experimental Procedure","content":"\u003cp\u003eThe chemical constituents of AA6351 alloy (wt %)) is given below. AA6351 alloy plates of thickness 6 mm are friction stir welded using the conical-shaped tool (shoulder dia-20mm, Pin dia.-6mm (base) to 3mm (tip) with pin length of 5.7mm, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The plates were welded (butt) length wise, using a 3-axis semi- automated milling machine.\u003c/p\u003e \u003cp\u003e \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 2.1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of AA6351 Al alloy (Wt %)\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=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" 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=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" 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=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.929\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.642\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.726\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e97.4\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\u003eDuring the post-weld heat treatment process, the samples are heated at 523\u0026deg;C for an 0.5 hour in a muffle furnace, followed by water quenching and then ageing in an oven at 177\u0026deg;C for 8 hours. A microstructural analysis of the Nugget zone (NZ), heat-affected zone (HAZ), and base metal of the weldment was conducted using optical microscopy (Olympus- BX53MRF) and SEM(scanning electron microscopy) with EDS (energy dispersive spectroscopy) (Model: JEOL JSM-IT500). Each and every figure included information about the voltage, detectors and working distance operated during SEM imaging. For in-depth chemical analysis, XRD (X-ray diffraction)-Rigaku manufacture, Miniflex 600 was utilized. The sample was prepared in accordance with ASTM E3 standard- scratch free, but without etching. According to ASTM E8 standard, tensile tests with extensometers were performed on base metal, FS, and PWH treated welds using UTM, Instron make-8801 at a constant strain rate-0.1 mm/sec. According to ASTM E384 standard, Micro-vickers hardness testing equipment, Model: Economet VH-1MDX was used to perform hardness testing with a 500g load. The tester had a dwell duration of 15 seconds and a total of 48 readings. The electrochemical system (Gill-AC) was utilized to investigate the weld sample\u0026rsquo;s pitting corrosion behavior, using a carbon electrode-auxiliary electrode, SCE-reference electrode. The testings were conducted in a 3.5% NaCl solution that was aerated, and the pH was adjusted to 10 by adding KOH.\u003c/p\u003e"},{"header":"3. Results and discussions","content":"\u003cp\u003eMicrostructural studies:\u003c/p\u003e\n\u003cp\u003eThe optical microstructures of AA6351 base metal in FS welded and PWH-treated conditions are depicted in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The microstructure shows longitudinally elongated grains of \u0026alpha;-Al matrix in dark color and a secondary phase in light color, which are present in both conditions. However, Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb shows a higher concentration of the light-colored secondary phase, which is likely due to the influence of solutionizing followed by ageing during PWHT. The macrostructures of FS weld and PWH treated sample shown, defect free weld joint with clearly distinguished various zones in weldment (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). From this macroscopic analysis, FS welded sample shown well-defined wavy interface between stir zone and TMAZ. Whereas PWH treated sample shown more homogenized macrostructure with vague zonal distribution. From Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, HAZ (as welded) exhibits a grain structure with coarse columnar grains, while the PWH-treated sample displays a microstructure with a finer grain size with uniformly distributed secondary phase and distinct features. The phase (secondary phase) which appears in dark color in PWH-treated microstructures is more likely to be Mg\u003csub\u003e2\u003c/sub\u003eSi, whereas the minute presence of this phase can be observed from the FS welded microstructures [\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e] (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). It may be due to partial dissolution of precipitation during welding. Due to their high stacking fault energy, aluminium alloys tend to form dense dislocation walls and dislocation tangles during deformation [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. These structures can then develop into partial boundaries of misorientation, which ultimately become sub-grain boundaries and result in grain refinement. As stir zone experiences severe plastic deformation while FS welding, the finer grain size can be observed in the stir zone of as welded and PWH treated conditions. In the TMAZ also, PWHT sample displays stress-free fine grains may due to solutionizing and ageing compared to FS-welded samples.\u003c/p\u003e\n\u003cp\u003eThe SEM microstructures of the stir zone shown uniformity in size, distribution and increased volume fraction of secondary phase (predominantly Mg\u003csub\u003e2\u003c/sub\u003eSi, from Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) in PWHT condition compared to FS weld condition. The partial dissolution of precipitates and fragmentation to the extent of negligable due to severe plastic deformation may resulted in the low no. of precipitates in FS welded condition. The elemental mapping of the stir zone shows an uneven phase distribution and elemental free zones in the microstructure of the weld sample. In contrast, there are no element-free zones in the PWH treated sample, which exhibits a consistent distribution of elements throughout the PWHT condition microstructure. This indicates that the PWH treated sample had a higher precipitation density than the weld sample.\u003c/p\u003e\n\u003cp\u003eThe X-ray diffraction analysis of FS weldment and PWH-treated sample shown distinguished peaks of Al (aluminium) which is major constiuent of the alloy. Additionally the presence of Mg\u003csub\u003e2\u003c/sub\u003eSi was identified according to JCPDS database, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. From comparing the Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb, the peaks of Mg\u003csub\u003e2\u003c/sub\u003eSi and Al evidently shows that substantial crystallographic adjustment during PWHT due to microstrucutre homogenization. The broadened yet distinct peak of Mg\u003csub\u003e2\u003c/sub\u003eSi in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb compared to FS welded sample may indicates the slight coarsening of precipitates during PWHT which are partially dissolved or, in negligable size. These microstructural variations often aids a significant modification in the properties of a weldment with more homogeneity, without attenuation of efficiency. These research findings helps in extending our understanding of the possible microstructural changes during FS welding in terms of size, composition and volume fraction.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMechanical properties\u003c/strong\u003e:\u003c/p\u003e\n\u003cdiv class=\"Heading\"\u003ea) Tensile studies:\u003c/div\u003e\n\u003cp\u003eTable 3.1. Tensile Properties of AA6351 FS Welds before and after PWHT\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"577\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"26.34315424610052%\" valign=\"top\"\u003e\n \u003cp\u003eWeld\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003eYield strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003eTensile Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.143847487001732%\" valign=\"top\"\u003e\n \u003cp\u003e% Elongation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003eFracture Zone\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"26.34315424610052%\" valign=\"top\"\u003e\n \u003cp\u003eAs weld\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003e143.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003e162.318\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.143847487001732%\" valign=\"top\"\u003e\n \u003cp\u003e13.0000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003eHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"26.34315424610052%\" valign=\"top\"\u003e\n \u003cp\u003ePWHT (STA)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003e177.754\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003e198.391\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.143847487001732%\" valign=\"top\"\u003e\n \u003cp\u003e10.6000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.504332755632582%\" valign=\"top\"\u003e\n \u003cp\u003eHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTable 3.1 shows the yield strength, tensile strength and % of elongation of FS welded and PWHT samples to analyze the tensile properties. In comparison to the weld sample, the PWH-treated sample demonstrates significantly improved tensile characteristics from the above data. According to the tensile values, the typical precipitation hardening phenomena was observed with an increase in the tensile strength of the PWHT sample. Though grain refinement supports the strength of FS weld sample due to formation of sub-grain boundaries, the amount of mechanical stresses generated during severe plastic deformation are detrimental to the mechanical behavior of FS welded sample. The dislocation tangles generated during welding can acts as initiating sites for micro cracks which have adverse effect on tensile behaviour of FS weld sample [27]. The partial dissolution of precipitates during FS welding, due to heat generation and fragmentation of precipitates due to severe deformation may contribute to the lower tensile properties of the FS weld sample in comparison to the PWH treated sample. The increase in the amount of precipitation during PWHT could be the reason for the reduction in elongation percentage, as these two factors are interconnected. And also stress relieving during PWHT and absence of PFZs which are formed due to dissolution of precipitates may responsible for better tensile strength value of PWHT sample [28]. Heat cycles during welding can cause HAZ to vary in grain morphology in both the welded and PWH treated states compared to base metal and stir zone. And the fracture position at HAZ clearly supports the above. 60% of the FS welded sample\u0026apos;s fracture surface is dimpled, while 40% is intergranular. In contrast, the PWHT sample exhibits 20% of dimple fracture and approximately 80% of intergranular fracture with fine grain structure. The formation of voids can be observed in FS weld sample, which can be nucleated at matrix and particle interface. The dislocation pile-up at grain boundaries by combining with localized stresses generated during FS welding may lead to the formation of voids as a consequence of de-cohesion. More fish eye (starting point of fracture) like structures are observed in FS welded condition in larger size compared to PWH treated condition. The coarser grain size was observed in FS weld sample with more ductile failure with dimpled structures. The homogenized microstructure with relieved stresses during PWHT are may be the reason for inter-granular failure of PWHT sample with very small \u0026nbsp;fraction of micro voids.\u003c/p\u003e\n\u003cp\u003eb) Hardness studies:\u003c/p\u003e\n\u003cp\u003eTable 3.2. Micro Vickers hardness values of AA6351, before and after PWHT\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"481\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.226611226611226%\" valign=\"top\" style=\"width: 11.6417%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eJOINT/WELD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"77.54677754677755%\" colspan=\"6\" valign=\"top\" style=\"width: 38.3159%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eHARDNESS VALUES ( in HV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.203319502074688%\" valign=\"top\" style=\"width: 11.6417%;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003eBM\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.9904%;\"\u003e\n \u003cp\u003eAHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.6858%;\"\u003e\n \u003cp\u003eATMAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003eSZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.4597%;\"\u003e\n \u003cp\u003eRTMAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.8774%;\"\u003e\n \u003cp\u003eRHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.406639004149376%\" valign=\"top\" style=\"width: 15.9367%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFSW-AW\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003e50.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.9904%;\"\u003e\n \u003cp\u003e61.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.6858%;\"\u003e\n \u003cp\u003e68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003e67.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.4597%;\"\u003e\n \u003cp\u003e62.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.8774%;\"\u003e\n \u003cp\u003e61.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.406639004149376%\" valign=\"top\" style=\"width: 15.9367%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFSW-STA\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.9904%;\"\u003e\n \u003cp\u003e81.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.6858%;\"\u003e\n \u003cp\u003e84.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.6513%;\"\u003e\n \u003cp\u003e86.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.4597%;\"\u003e\n \u003cp\u003e83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.8774%;\"\u003e\n \u003cp\u003e80.38\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBy comparing the hardness values of base metal, FS weld and PWH treated samples, PWH treated sample shows better hardness (Table 3.2). less gradient was observed in the hardness values of various zones of PWH treated weldment. The uniform distribution of precipitates and their increased volume fraction due to reprecipitation may attributed to the enhanced hardness values of PWH treated sample than FS weld sample. The relationship between fine grain size and increased hardness suggests that grain size and no. of precipitates have a significant impact on the hardness increase. The HAZ which contains coarser grain size evidently shown lower hardness when compared to remaining zones. The modified texture in the TMAZ may contribute to the increase in hardness, with the retreating side TMAZ exhibiting lower hardness than the advancing side. This variation in hardness can be ascribed to the longer heat residing time due to material deposition at the retreating side, leading to coarser grain size.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrosion studies:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 3.3. Pitting potential (E\u003csub\u003epit\u003c/sub\u003e) values of AA6351, before and after PWHT\u003c/p\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"481\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.226611226611226%\" valign=\"top\" style=\"width: 11.6747%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eJOINT/WELD\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"77.54677754677755%\" colspan=\"6\" valign=\"top\" style=\"width: 38.3111%;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePitting potential (E\u003csub\u003epit\u003c/sub\u003e)\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e( in mV)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.203319502074688%\" valign=\"top\" style=\"width: 11.6747%;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003eBM\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003eAHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.7076%;\"\u003e\n \u003cp\u003eATMAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003eSZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.5942%;\"\u003e\n \u003cp\u003eRTMAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003eRHAZ\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.406639004149376%\" valign=\"top\" style=\"width: 16.0952%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAW\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003e-684\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003e-653\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.7076%;\"\u003e\n \u003cp\u003e-637\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003e-601\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.5942%;\"\u003e\n \u003cp\u003e-667\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003e-650\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"22.406639004149376%\" valign=\"top\" style=\"width: 16.0952%;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePWHT(STA)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003e-618\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003e-590\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.352697095435685%\" valign=\"top\" style=\"width: 7.7076%;\"\u003e\n \u003cp\u003e-551\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 5.4406%;\"\u003e\n \u003cp\u003e-534\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.937759336099585%\" valign=\"top\" style=\"width: 7.5942%;\"\u003e\n \u003cp\u003e-565\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.825726141078839%\" valign=\"top\" style=\"width: 6.0074%;\"\u003e\n \u003cp\u003e-598\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eFrom the Fig 11, The E\u003csub\u003epit\u003c/sub\u003e values shows overall better corrosion resistance values in PWH treated sample, compared to FS weld sample. Fig 11.b depicts the E\u003csub\u003epit\u003c/sub\u003e value of -534mV at stir zone, which has higher corrosion resistance among all the other zone. It can be attributed to the coherent reprecipitation and their uniform distribution [29-30]. In addition, the stir zone curve showed a greater degree of passivity in comparison to both the post weld and FS weld samples. The presence of more number of precipitates, which serve as a barrier to inhibit corrosion attack, is responsible for the increased passivity that was observed from the stir zone curve. The coherency of these precipitates also significantly contributes to the improved corrosion resistance of stir zone curve. The better corrosion resistance observed in both the advancing and retreating side TMAZ in PWHT condition may be attributed to reduced sensitivity caused by residual stresses generated during the FS welding process. The lower corrosion resistance observed in the FS-weld HAZ, as compared to the FS-weld SZ, TMAZ, and PWHT samples, may be due to the coarsening of existing precipitates and their non-uniform distribution [31-33]. The enhanced corrosion resistance observed after solutionizing and ageing (STA) may be attributed to the replacement of severely deformed grains with stress-free recrystallized grains. In FS welded condition, the dislocation tangles generated during FSW can act as potential corrosion initiation sites with their higher energy. In the as-welded sample, the presence of precipitate free zones (PFZs), which are formed as a result of frictional heat generated during FS welding, promotes corrosion due to galvanic coupling with the \u0026alpha;-Al solid solution matrix. Additionally, preferential grain boundary corrosion is a potential factor to the lower corrosion resistance that has been observed from FS-welded sample. The homogeneity achieved across the microstructure through PWHT process has a substantial impact in strengthening the weldment resistance to corrosion compared to the FS-welded sample.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe microstructure, mechanical characteristics, and pitting corrosion behavior of AA6351 (FS weld) and PWH treated state were compared in the present study. The key findings of the current study are as follows:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe microstructure of the FS welded condition exhibits the dissolution of finer precipitates and partial dissolution of secondary phases, resulting in the formation of PFZs. In contrast, the PWH treated sample shows a homogenous microstructure with uniform reprecipitation due to the solutionizing along with ageing processes.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe PWH-treated sample has shown surpassing mechanical properties compared to the FS welded sample, due to their uniform distribution and increased volume fraction of precipitation throughout the microstructure. This has played a significant role in improving the properties, resulting in better mechanical behavior, including yield and tensile strength.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe lower pitting corrosion resistance observed in the FS-welded sample may be due to galvanic coupling, while the PWH-treated sample exhibits better pitting corrosion resistance due to the presence of coherent precipitates.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eThe overall properties of mechanical and pitting corrosion behaviour of PWH treated FS weld joint shows better results compared to FS weld joint, with less gradient in hardness values, enhanced strength in tensile values, and higher pitting corrosion resistance. These benefits can be attributed to the fact that the weld joint attained homogeneous chemistry and microstructure through PWHT.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose. The authors have no conflicts of interest to declare that are relevant to the content of this article\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eN. Yuvaraj, V. Mohanavel, M. Ravichandran, B. N. Sreeharan, en T. Kannan, \u0026ldquo;The effect of welding parameters on surface quality of AA6351 aluminium alloy The effect of welding parameters on surface quality of AA6351 aluminium alloy\u0026rdquo;, bll 1\u0026ndash;6, 2015, doi: 10.1088/1757-899X/100/1/012038.\u003c/li\u003e\n\u003cli\u003eF. O. F. 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Chen, S. Li, en L. H. Hihara, \u0026ldquo;Microstructure, mechanical properties and corrosion of friction stir welded 6061 Aluminum Alloy\u0026rdquo;.\u003c/li\u003e\n\u003cli\u003eB.S. Nair, S. Rakesh, G. Phanikumar, K.P. Rao, P.P. Sinha. Fracture toughness (J1C) of electron beam welded AA2219 alloy. Mater Des 2010; 31: 4943-4950.\u003c/li\u003e\n\u003cli\u003eS. Malarvizhi, K. Raghukandan, N. Viswanathan. Investigations on the influence of post weld heat treatment on fatigue crack growth behaviour of electron beam welded AA2219 alloy. Int J Fatigue 2008; 30: 1543-1555.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"FSW, AA6351, PWHT, SEM, Mechanical properties, Pitting","lastPublishedDoi":"10.21203/rs.3.rs-4208352/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4208352/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAl-Mg-Si (6xxx) alloys have superior properties to other aluminium alloys, making them suitable for aerospace and defence applications. However, their weldments are susceptible to various issues that affect their microstructural changes, mechanical properties, and corrosion resistance. The use of friction stir welding has been proven to be an effective solution for these problems, and this study aimed to investigate the microstructural changes, mechanical properties, and pitting potential (Epit) of AA6351 alloy friction stir welds. The present study used AA6351 with a thickness of 6mm alloy plates for welding and characterized the welds' microstructure, pitting corrosion resistance, and mechanical properties of hardness and tensile strength. Post-weld heat treatment (PWHT) for solutionizing at 523\u0026deg;C for 0.5hrs followed by 8 hrs at 177⁰C (STA-solutionizing treatment with ageing) was applied to improve the welds' corrosion resistance and mechanical properties. A comparison between the base metal and weldment before and after PWHT showed that the ageing treatment of the welds improved their mechanical properties and pitting corrosion resistance. This treatment caused re-precipitation and redistribution of precipitates in the welds\u0026rsquo; grain-refined stir zone, restoring their mechanical properties and pitting corrosion resistance. Therefore, this study established that post-weld solutionizing at 523\u0026deg;C for 0.5 hrs and then ageing at 177⁰C for 8hrs can restore the overall mechanical and pitting corrosion behaviour of AA6351 alloy friction stir welds.\u003c/p\u003e","manuscriptTitle":"Effect of post-weld heat treatment on AA6351 friction stir welds","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-10 03:27:40","doi":"10.21203/rs.3.rs-4208352/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"aa1e4e85-08fb-4262-9a2a-b161557e26fd","owner":[],"postedDate":"April 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-03T04:39:41+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-10 03:27:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4208352","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4208352","identity":"rs-4208352","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}