Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy

Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 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 Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy Aiman H. Al-Allaq, Manish Ojha, Yousuf S. Mohammed, Srinivasa N. Bhukya, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2720330/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Oct, 2023 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted 4 You are reading this latest preprint version Abstract Post weld heat treated AA6061-T6 alloy resulted from the application of a Cu donor stir assisted (CDSA) friction stir welding (FSW) material was examined for crystal structure and mechanical properties. CDSA FSW samples were tested at a constant tool rotational speed of 1400 rpm and a welding translational speed of 1 mm/s. CDSA samples of 20% and 60% thickness of the AA6061-T6 base alloy were selected to assist the FSW joining at the plunge stage. The FSW AA6061-T6 samples were solid solution treated at 540 °C for one hour, followed by quenching in water at room temperature. The samples were then artificially aged at 180 °C for 6 hours, respectively, followed by air cooling. The samples were tested for microstructure, crystal structure, chemical composition, and mechanical properties using optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation. The microstructure shows the additional grain refinement in the stir zone (SZ) due to recovery and recrystallization with increasing aging time. Examination of the chemical contents of the FSW AA6061-T6 alloy samples using scanning electron microscopy with energy dispersive spectroscopy (EDS) revealed Al (parent material) as the predominant element, while Cu (CDSA) was minimally present as expected. XRD results of the CDSA FSW samples depicted crystal orientations similar to the orientations of the AA6061-T6 alloy. Nanoindentation tests revealed softening effects due to the dissolution of hardening precipitates at the SZ. The hardness of the base metal (BM), left and right regions, is reported as ~ 6.5 GPa, whereas at the SZ, the hardness is ~ 5.5 GPa at a depth of indentation of 4.7 µm. Friction stir welding Micro-structured/surface characterization Heat treatment processes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1.0 Introduction Lightweight materials possess unique properties that are of great interest to DoD industries. Aluminum alloys (AA) represent lightweight materials used in various military applications due to their high strength-to-weight ratio and low fabrication cost compared to steel, titanium, and magnesium alloys. Aluminum alloys AA5083, AA2139, and AA7039 are often used in armored vehicles and military vessels [ 1 ]. These alloys meet the military standards for projectile resistance, corrosion resistance, lightweight, and weldability. Ballistic and armor-piercing tests are commonly performed on aluminum armored plates to ensure the strength and safety requirements are met for military applications. Although these alloys are used in armored vehicles, the complexity in manufacturability and sustainment of selecting appropriate aluminum alloys for vehicles' hull structures increased due to the lack of sufficient and efficient welding techniques. These aluminum alloys perform poorly in conventional fusion welding. FSW, a solid-state welding process, emerged as a promising alternative for welding aluminum alloys and overcoming defects such as porosities, solidification cracking, high residual stress, etc., generally associated with fusion welding[ 2 ]. FSW produces low-cost quality welds compared with other welding processes. However, the loss of strength due to heat generation at the weld zone during welding is still a major concern [ 3 – 6 ]. For example, for gas metal arc welded (GMAWed) of AA2139-T8 alloys, weld strength, and elastic elongation, which are measures of the weld quality, are only 35–55% of the base material. To strengthen aluminum alloy weldments, a solution heat treatment followed by rapid water quenching is recommended [ 6 ]. This solution heat treatment process results in a metallurgical structure within the alloy that enhances the strength of the weld [ 7 ]. The formation and distribution of precipitants depend on the solution treatment temperature and the artificial aging time levels. Si and Mg are the two major alloying elements of the 6000-aluminum series that are typically added in the proportions required for the formation of hardening precipitates of Mg 2 Si. Since Mg 2 Si constitutes the main precipitants of the 6000-aluminum alloy series, this results in making the 6000-aluminum alloy series heat treatable by solutionizing and artificial aging processes. Heat treatment influences the internal microstructure and hence the mechanical properties of metals and alloys, including hardness, yield strength, ultimate tensile strength, and corrosion resistance. Metals and alloys can be processed using various heat treatment approaches, such as changing the solutionizing temperatures and using different aging time levels [ 8 ]. Several manufacturing industries follow ASTM B917 and ASTM B91 standards for precipitation hardening or the so-called "T6 heat treatment". T6 heat treatment involves a solution heat treatment at a temperature of 540°C with a residence duration between 6 to 12 hours, followed by artificial aging at 155°C between 3 to 5 hours [ 9 ]. Rosso and Actis suggested that solutionizing metals for 1 hour rather than 6 hours would yield significantly better tensile strength. They also concluded that further subjecting metals to 180°C for 4 hours using artificial aging would yield better mechanical properties [ 10 ]. Shivkumar et al. [ 11 ] and Zhang et al. [ 12 ] concluded that a solution heat treatment temperature of 540°C followed by the artificial aging time between 3–5 hours at 155°C is sufficient to yield better hardness and strength. Cabibbo et al. [ 13 ] studied the effect of post weld heat treatment (PWHT) on FSW of AA6056 alloy and reported a significant increase in the tensile strength due to the formation of high-density precipitation of Mg 2 Si. Jamshidi and Serajzadeh [ 14 ] also reported that artificial aging increased the hardness of the friction stir welded AA6061 alloy. Although the formation of fine recrystallized grains, the dissolution and growth of precipitates were noticed in the weld zone after FSW [ 5 ]. Aging resulted in the formation of hardening precipitates, which led to a full recovery of the mechanical properties. Previous studies indicated that post-artificial aging is necessary to produce sufficient strength and hardness at the weld zone of a friction stir processing of 6000 series aluminum alloys. Priya et al. [ 15 ] investigated the PWHT on FSW AA6061-T6 and AA 2219-T6 alloys and concluded that their ultimate tensile strength was increased due to the presence of fine precipitated particles. Hu et al. [ 16 ] performed PWHT of friction stir welded AA2024 alloys and noticed that their mechanical properties were not changed but enhanced the weld's elongation. Aydin et al. [ 17 ] studied solution heat treatment followed by an aging process on friction stir welded AA2024-T6 alloy and reported that the mechanical properties were significantly enhanced at 190°C for 10h artificial aging compared to natural aging. Recently, Bhukya et al. [ 18 ] reported the effects of using copper donor stir assisted material of FSW of AA6061‑T6 alloy on the microstructure and mechanical properties of the welded specimens but not on PWHT. The PWHT research work has been accomplished on regular FSW aluminum alloys. However, the effect of PWHT on Cu donor stir assisted FSW AA6061-T6 alloy has not yet been investigated. This study used various techniques to investigate the chemical, microstructure, and mechanical properties, including FE-SEM, XRD, SEM-EDS, optical microscopy, and nanoindentation. The samples were subjected to a solid solution heat treatment at 540°C for 1 hour, followed by artificial aging for 0 and 6 hours at 180°C. 2.0 Experimental Procedure The CDSA sample preparation is detailed in [ 18 ]. In this study, a base metal of extruded AA6061-T6 alloy sheets with dimensions of 304.8 mm (length)×76.2 mm (width)×6.35 mm (thickness) was used to fabricate the test coupons. Test coupons, with dimensions of 152.4 mm (length)×76.2 mm (width), were sectioned from the as-received sheets, and the edges were milled along the length. A trough with dimensions of 63.5 mm (length)×25.4 mm (width) was forged onto the workpieces for positioning the donor stir-assisted material. Before welding, the trough and the donor stir-assisted material were cut and shaped using a CNC mill. A CDSA with 20% and 60% of the AA6061-T6 alloy thickness were selected for the current investigation. Tables 1 and 2 list the chemical composition and mechanical properties of the AA6061-T6 and Cu-110 alloys, respectively. FSW experiments were conducted in the position control mode, using a triangle tapered pin-type tool head made of H13 steel. More information about the FSW machine used in this study can be found in [ 18 ]. The joints were friction stir butt-welded at a translational welding speed of 1mm/s and a tool rotation of 1400 rpm. Table 1 Chemical composition of AL6061-T6 and Cu 110 alloys. Alloy Al Cu Cr Fe Mg Mn Si Ni Ti Zn Zr Other A6061-T6 95–98 0.05–0.05 0.4–0.8 0.01–0.7 0.8–1.2 0.01–0.15 0.001–0.05 0.001–0.05 0.001–0.15 0.001–0.25 0.001–0.25 0.15 Cu 110 - 99.9 - - - - - - - - - 0.005 − 0.004 Table 2 Mechanical properties of Cu 110 and Al6061-T6. Material A6061-T6 Cu 110 Rockwell Hardness 40–60 55 Yield strength MPa 241 255 Ultimate strength MPa 262 345 Thermal conductivity W/mK 151 183 Melting Point °C 585 1084 The influence of PWHT on the mechanical/structural properties was investigated by dividing the weldments into two groups: As-Welded (AW) and heat-treated (HT) samples. The heat treatment process involved solution heat treatment in the furnace at a temperature of 530°C for 1 hour, followed by immediate water quenching. The samples were then artificially aged inside the furnace at a temperature of 180°C for 0 and 6 hours. The heat-treated metallography samples were cold-mounted, ground, polished, and etched with Keller's reagent for approximately 120 seconds to reveal the grain structure. An Olympus optical microscopy with quantitative image analysis software was used for microstructure and macrostructure studies. The friction stir welded coupons were sectioned using a wire electrical discharge machine (WEDM) in the direction perpendicular to the welding direction (WD) to examine the microstructures in the weld cross-sections. The fractured surface of the friction stir welded samples were subsequently examined using a JEOL 6700 FE-SEM equipped with three-dimensional (3-D) fractographic analysis capacity. Indentation experiments were conducted on the AW samples using a Nanoindenter XP with a high-load attachment for the XP head that could apply a load of up to 10 N. The standard XP head and high load attachment enabled experiments from the nano to the micro regime using a single Berkovich diamond indenter tip. The nanoindenter tip was calibrated using a standard fused silica standard. Each indentation was made using the standard NanoSuite XP continuous stiffness method (CSM) protocol with a maximum depth of 5um. 3.0 Results And Discussion 3.1. Microstructure analysis Figure 1 (a-c) shows the microstructure of the 20% CDSA, the 0, and 6 hours solution treated AA6061-T6 samples. The samples represent the SZ location. The microstructure in the SZ consists of grains with slightly uneven boundaries, perhaps resulting from the high plastic deformation during the FSW process and the dissolution of the strengthening particles commonly occurring in the T6-treated base plate. Small grains were formed, and the grain size increased with the solution treatment time, Fig. 2 (a-b). The FE-SEM of Fig. 2 b depicts smaller dark particles of the PWHT sample. These particles were not present in the FE-SEM of the AW sample PWHT precipitated strengthening particles in the SZ, as shown in Fig. 2 (a). The development of the small dark particles in the PWHT is attributed to the presence of the Mg 2 Si intermetallic contents [ 20 ]. This type of particle development can generally be found in AA6061-T6 alloy when the alloy undergoes heat treatment followed by an artificial aging process. The precipitation microstructure of Mg 2 Si during aging for AA 6061-T6 alloys is well documented in the literature [ 20 – 22 ]. The number of intermetallic particles increases with the increase of the aging time. Equiaxed grains with fine grain size were formed and increased with the increase of the time of aging for the PWHT. 3.2. SEM, EDS observations SEM-EDS was used to evaluate the impact of the CDSA on the FSW AA6061-T6 alloy samples. Examination of the chemical contents of the FSW AA6061-T6 alloy samples indicated the dominance of Al (parent material), whereas CDSA was somewhat detected. The tests were performed for the base metal BM (left region), BM (right region), and the SZ zone (middle region). Figure 4 shows EDS plots of the 20% and 60% CDSA, solution treated (ST), and 6 hours heat treated (HT) FSW AA6061-T6 alloy samples taken at several points at the SZ. Figures 3 (a) and (b) represent the 20% and 60% ST samples, while Figs. 3 (c) and (d) represent the 20% and 60% 6-hour HT samples. Tables 3 (a-d) list elements' composition percentages at each point referenced in Fig. 3 . Al is the major element, while other elements such as C, Fe, Mg, Mn, O, and Si exist in a small percentage. It is evident from the EDS images and the listing of the chemical elements at the SZ that the absence of the Cu element of the CDSA material is anticipated. EDS plots of FSW samples with 20% and 60% CDSA ST and 6 hours CDSA HT samples at the SZ and BM regions are shown in Fig. 4 , respectively. The plot unequivocally depicts Al as the major element in all samples. Al was also found to be the major element in the SEM-EDS analysis performed for a nanoindentation imprint in the SZ, as seen in Fig. 5 . As we reported, other elements also existed but in very small percentages. Table 3 (a) Weight % of the elements for the 20% ST CDSA at the SZ Location C O Mg Al Si Mn Fe ST-M 20%(1)_pt1 7.03 ND ND 73.36 4.99 1.29 13.33 ST-M 20%(1)_pt2 9.73 1.23 ND 83.80 1.28 ND 3.96 ST-M 20%(1)_pt3 10.36 ND 6.41 75.99 4.39 ND 2.84 ST-M 20%(1)_pt4 11.38 0.76 1.33 85.66 0.87 ND ND ST-M 20%(1)_pt5 11.42 1.59 ND 86.99 ND ND ND ST-M 20%(1)_pt6 11.87 ND ND 88.13 ND ND ND Table 3 (b) Weight % of the elements for the 60% ST CDSA at the SZ Location C O Mg Al Si Fe ST-M 60%(1)_pt1 9.01 2.08 1.16 68.15 6.89 12.72 ST-M 60%(1)_pt2 8.99 2.98 0.26 67.82 6.45 13.50 ST-M 60%(1)_pt3 7.27 2.18 0.34 81.11 2.86 6.24 ST-M 60%(1)_pt4 7.42 9.79 0.46 79.01 3.32 ND ST-M 60%(1)_pt5 7.96 2.83 0.45 88.76 ND ND Table 3 (c) Weight % of the elements for the 20% 6-hour HT CDSA at the SZ Location C O F Mg Al Si Mn Fe HT6-M 20%(1)_pt1 7.66 ND ND 1.88 70.01 5.79 1.48 13.19 HT6-M 20%(1)_pt2 6.83 1.33 ND 0.40 82.21 2.79 ND 6.43 HT6-M 20%(1)_pt3 6.84 ND ND 0.79 86.84 1.67 ND 3.86 HT6-M 20%(1)_pt4 6.49 19.79 0.83 ND 52.25 20.64 ND ND HT6-M 20%(1)_pt5 5.42 0.90 ND 0.61 93.06 0.00 ND ND Table 3 (d) Weight % of the elements for the 60% 6-hour HT CDSA at the SZ Location C O Mg Al Si K Fe HT6-M 60%(1)_pt1 6.27 2.23 0.93 81.70 3.04 ND 5.84 HT6-M 60%(1)_pt2 8.80 9.44 1.30 73.39 5.29 1.78 ND HT6-M 60%(1)_pt3 6.36 3.35 0.38 75.55 5.12 ND 9.24 HT6-M 60%(1)_pt4 11.15 13.55 2.30 65.68 7.32 ND ND HT6-M 60%(1)_pt5 6.36 2.51 0.44 90.69 ND ND ND ND* - not detectable. 3.3. XRD analysis The XRD results are presented in the plot of Fig. 6 . The plot includes 20%, 60% DCSA zero hours ST, 6 hours HT, and BM samples. In addition to the presence of Al at several peaks [ \(2{\theta }(^\circ )=37.50, 64.07, 77.32, and 81.55]\) , other elements such Al 2 O 3 , Mg 2 Si, Al 8 Fe 2 Si, Al(FeMnCr)Si, and Al+Al 2 O 3 existed with smaller amounts at peaks of \(2{\theta }\left(^\circ \right)=36.14, 39.54, 41.56, 42.35 and 43.51,\) respectively. Figure 7 shows the XRD patterns of the 20%, 60% DCSA zero hours ST, 6 hours HT, and BM samples. Again, the diffraction peaks are labeled in the Figure. It is also observed that the samples depicted aluminum cubic and Al, Fe, and Si systems of hexagonal crystal structure. 3.5. Nanohardness measurements The nanoindentation plot of Fig. 8 indicated the softening effect in SZ of the 20% Cu 6 hours heat treated samples. The hardness at the SZ was measured as 0.55 GPa compared to a hardness of 0.63 GPa for the BM fat, with a depth of indentation of 4.75 \(\mu m\) . 3.6. Fractography Figure 9 (a-d) and Fig. 10 (a-b) show fracture surfaces of the 1400 rpm and 1 mm/s of as welded and 6 hours heat treated samples. These fractographic images include crack initiation, spherical and broken dimples, secondary cracks, tear ridges, and particles. It is noted that crack initiation occurs in the vicinity of the TMAZ/HAZ retreating side following the PWHT, Fig. 10 a. The fracture surface presents many small spherical dimples with layered distribution, which often indicates a ductile fracture. The 20% CDSA AW samples exhibited intergranular cracking with coarser dimples. The dimples were becoming finer for the PWHT welded samples, and the emerging grains were getting smaller than the AW's grain when the aging time was increased, Fig. 10 b. 3.7. Conclusions The present research aims to investigate the microstructure, crystal structure, chemical composition, and mechanical properties of the welded joints of 20% and 60% CDSA PWHT samples. Optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation techniques were utilized. The results are as follows: The SZ and the TMAZ, predominantly composed of equiaxed grains, experienced complete dynamic recrystallization. The grain size in the SZ became finer after PWHT, followed by 6 hours artificial aging process. A significant amount of strengthening intermetallic particles of Mg 2 Si was observed after PWHT, which changed the structure of the AA6061-T6 alloy. After the PWHT, there was a sudden increase in the hardness at the center of the weld. The SZ is softer than the BM from the nanoindentation hardness results. Fractography of the AW tensile testing fractured samples exhibited intergranular cracking with large dimples. The fractured surface for the PWHT samples exhibited a ductile-like fracture with a large number of fine dimples. These dimples emerged in the ductile fractured surfaces, which only correspond to voids. For the PWHT joint, the dimples were becoming finer, and the grains that emerged were smaller than the AW when the aging time was increased. Declarations 1. What is your main contribution to the field? The primary contribution of this research, entitled "Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Cu Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy," is the analysis of the effects of post weld heat treatment on the microstructure, crystal structure, chemical composition, and mechanical properties of AA6061-T6 alloy welded joints produced using Cu donor stir assisted friction stir welding. In this research, we concluded that the stir zone exhibited grain refinement after the heat treatment and artificial aging process, which led to the formation of strengthening intermetallic particles of Mg 2 Si. In addition, nanoindentation test results showed that the hardness results of the base metal (BM), which is represented by the left and right regions are consistent with the hardness of the AA6061-T6 hardness results. Furthermore, the stir zone experienced softening as compared to the base metal. These findings offer important insights and guidelines for optimizing welding processes and post-weld heat treatments to enhance the performance and durability of welded structures made from the AA6061-T6 alloy. 2. What is novel? In theory, in experimental techniques, or a combination of both? In our research on "Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Cu Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy," The novelty lies in using high characterization techniques to identify post weld heat treatment and how it impacts the crystal structure, microstructure, chemical composition, and mechanical properties of the welded AA6061-T6 joints. Our research revealed that the stir zone exhibited grain refinement after the heat treatment and artificial aging process, leading to the formation of strengthening intermetallic particles of Mg 2 Si. We measured the hardness of the base metal (BM), left and right regions as ~ 6.5 GPa, whereas at the SZ, the hardness is ~ 5.5 GPa at a depth of indentation of 4.7 µm. 3. Does your paper have industrial applications? If yes, who are the likely user? The research findings and recommendations could be advantageous to industries such as transportation, aviation, maritime, and civil engineering by providing insights to enhance welding processes and post-weld heat treatment procedures. This, in turn, could contribute to the improvement of performance and longevity of welded joints made from AA6061-T6 and other alloys. As a result, the intended users of this research include materials engineers, industrial specialists, and fabrication professionals working across these various sectors. Acknowledgments The authors express their gratitude for the funding support from NASA (grant ID: 80NSSC20M0015). ZW appreciates the support from ONR (grant ID: N00014-19-1-2728). This document's perspectives, discoveries, deductions, or suggestions belong to the author(s) and do not necessarily represent NASA and ONR's viewpoints. The authors acknowledge the Commonwealth Center for Advanced Manufacturing (CCAM) and Amsted Rail for making available the infrastructure required for specimen evaluation. Finally, the valuable contribution of Mr. Geoff Widman in carrying out the experiments is acknowledged and appreciated. a. Funding: The authors would like to acknowledge support from NASA (award number: 80NSSC20M0015). The author ZW also acknowledges support from ONR (award number: N00014-19-1-2728). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NASA and ONR. b. Competing Interests : The authors have no relevant financial/non-financial interest neither conflict of interest to disclose. c. Author Contributions: Mr. A. H. Al-Allaq performed XRD characterization and wrote/revised the manuscript. Dr. S. Bhukya carried out experimentation and data analysis for the CDSA and revised the manuscript. Dr. A.A. Elmustafa conceptualized the research and wrote/revised the manuscript. Dr. Z. Wu secured the funding. Mr. M. Ojha performed the SEM-EDS and Dr. Y. Mohammed performed the nanoindentation testing. References Grujicic M, Arakere G, Pandurangan B, et al (2011) Development of a Robust and Cost-Effective Friction Stir Welding Process for Use in Advanced Military Vehicles. J Mater Eng Perform 20:11–23. https://doi.org/10.1007/s11665-010-9650-0 Thomas WM, Nicholas ED, Needham JC, et al. (1995) Friction welding Kallee SW, Nicholas D (2006) Friction stir welding at TWI. The Welding Institute (TWI): Cambridge, England Thomas WM, Dolby RE (2003) Friction stir welding developments. Proceedings of the sixth international trends in welding research 203–211 Jata K v., Semiatin SL (2000) Continuous dynamic recrystallization during friction stir welding of high strength aluminum alloys. Scr Mater 43:743–749. https://doi.org/10.1016/S1359-6462(00)00480-2 Lakshminarayanan ak, Balasubramanian V (2008) Process parameters optimization for friction stir welding of RDE-40 aluminum alloy using Taguchi technique. Transactions of Nonferrous Metals Society of China 18:548–554. https://doi.org/10.1016/S1003-6326(08)60096-5 Valery IR, Don L, Raymond C (2002) Handbook of Induction Heating: Manufacturing Engineering and Materials Processing Davis JR (1993) Aluminum and aluminum alloys. ASM International Menargues S, Martín E, Baile MT, Picas JA (2015) New short T6 heat treatments for aluminum silicon alloys obtained by semisolid forming. Materials Science and Engineering: A 621:236–242 Rosso M, Actis Grande M (2006) Optimization of heat treatment cycles for automotive parts produced by rheocasting process. In: Solid State Phenomena. Trans Tech Publ, pp 505–508 Shivkumar S, Ricci S, Steenhoff B, et al. (1989) An experimental study to optimize the heat treatment of A356 alloy. AFS Transactions 97:791–810 Zhang DL, Zheng LJ (1996) The quench sensitivity of cast Al-7 wt pct Si-0.4 wt pct Mg alloy. Metallurgical and Materials Transactions A 27:3983–3991 Cabibbo M, McQueen HJ, Evangelista E, et al. (2007) Microstructure and mechanical property studies of AA6056 friction stir welded plate. Materials Science and Engineering: A 460–461:86–94. https://doi.org/https://doi.org/10.1016/j.msea.2007.01.022 Jamshidi Aval H, Serajzadeh S (2014) A study on natural aging behavior and mechanical properties of friction stir-welded AA6061-T6 plates. The International Journal of Advanced Manufacturing Technology 71:933–941. https://doi.org/10.1007/s00170-013-5531-7 Priya R, Subramanya Sarma V, Prasad Rao K (2009) Effect of post weld heat treatment on the microstructure and tensile properties of dissimilar friction stir welded AA 2219 and AA 6061 alloys. Transactions of the Indian Institute of Metals 62:11–19. https://doi.org/10.1007/s12666-009-0002-4 Hu Z, Yuan S, Wang X, et al. (2011) Effect of post-weld heat treatment on the microstructure and plastic deformation behavior of friction stir welded 2024. Mater Des 32:5055–5060. https://doi.org/https://doi.org/10.1016/j.matdes.2011.05.035 Aydın H, Bayram A, Durgun İ (2010) The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-welded joints. Materials & Design (1980-2015) 31:2568–2577. https://doi.org/https://doi.org/10.1016/j.matdes.2009.11.030 Bhukya SN, Wu Z, Maniscalco J, Elmustafa A (2022) Effect of copper donor material-assisted friction stir welding of AA6061-T6 alloy on downward force, microstructure, and mechanical properties. The International Journal of Advanced Manufacturing Technology 119:2847–2862. https://doi.org/10.1007/s00170-021-08390-8 ASTM Standard Test Methods for Tension Testing of Metallic Materials, ASTM E8 Khalili V, Heidarzadeh A, Moslemi S, Fathyunes L (2020) Production of Al6061 matrix composites with ZrO2 ceramic reinforcement using a low-cost stir casting technique: Microstructure, mechanical properties, and electrochemical behavior. Journal of Materials Research and Technology 9:15072–15086. https://doi.org/10.1016/J.JMRT.2020.10.095 Khalil O, Mingareev I, Bonhoff T, et al. (2014) Studying the effect of zeolite inclusion in aluminum alloy on measurement of its surface hardness using laser-induced breakdown spectroscopy technique. Optical Engineering 53:014106. https://doi.org/10.1117/1.OE.53.1.014106 Woo W, Ungár T, Feng Z, et al. (2010) X-Ray and Neutron Diffraction Measurements of Dislocation Density and Subgrain Size in a Friction-Stir-Welded Aluminum Alloy. Metallurgical and Materials Transactions A 41:1210–1216. https://doi.org/10.1007/s11661-009-9963-5 Cite Share Download PDF Status: Published Journal Publication published 10 Oct, 2023 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Reviewers invited by journal 20 Apr, 2023 Reviewers agreed at journal 28 Mar, 2023 Editor assigned by journal 27 Mar, 2023 First submitted to journal 24 Mar, 2023 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-2720330","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":187312132,"identity":"8a993c5d-2c9a-45e1-af3d-f1130a29abfc","order_by":0,"name":"Aiman H. Al-Allaq","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Aiman","middleName":"H.","lastName":"Al-Allaq","suffix":""},{"id":187312133,"identity":"29fc3e4e-871f-4c32-b3e0-dd487132851f","order_by":1,"name":"Manish Ojha","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Manish","middleName":"","lastName":"Ojha","suffix":""},{"id":187312134,"identity":"3407d2ec-6ccc-4797-9ef9-79207d4c2639","order_by":2,"name":"Yousuf S. Mohammed","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yousuf","middleName":"S.","lastName":"Mohammed","suffix":""},{"id":187312135,"identity":"fe85b60c-3428-4966-a16e-0d3a13872da7","order_by":3,"name":"Srinivasa N. Bhukya","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Srinivasa","middleName":"N.","lastName":"Bhukya","suffix":""},{"id":187312136,"identity":"2ce57720-2d07-427a-8460-a2ef0f90ed0e","order_by":4,"name":"Zhenhua Wu","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhenhua","middleName":"","lastName":"Wu","suffix":""},{"id":187312137,"identity":"83e4d4aa-ce69-44a4-9649-331af4a38d02","order_by":5,"name":"Abdelmageed A. Elmustafa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYFAC5gYwxc/AYADiEaOFEaTFgEGygWQtBgeI1cLf3ti6mefPH3nj483bJBgqrBMbCGmROHOw7TZvm4HhtjPHyiQYzqQT1sJwIxGopcGAcduNHDMJxrbDhLXI33/Ydpvnj4H95hkgLf+I0GJwgxGohc0gcYMESEsDEVoMzyS23ZzbZpw848yxYouEY+nGBLXIHT987MabP3K2/e3NG298qLGWJagFFSSQpnwUjIJRMApGAS4AAAU4QgTS8WYTAAAAAElFTkSuQmCC","orcid":"","institution":"Old Dominion University Frank Batten College of Engineering and Technology","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Abdelmageed","middleName":"A.","lastName":"Elmustafa","suffix":""}],"badges":[],"createdAt":"2023-03-21 22:20:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2720330/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2720330/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-023-12407-9","type":"published","date":"2023-10-10T15:02:33+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":35048646,"identity":"c994c7e3-ad44-466a-8684-ace0fd79edcf","added_by":"auto","created_at":"2023-03-30 15:34:05","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2069406,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microstructure images after PWHT at SZ of joints made at 20% Cu, 1400 rpm, and one mm/s, a) 20% Cu A, b) ST+AA 0Hr, and c) ST+ AA 6 Hr\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/e2bffaecf8b706a8ea43e578.jpeg"},{"id":35050286,"identity":"f723b6a4-7b98-4c28-a5bf-28df15c1eec4","added_by":"auto","created_at":"2023-03-30 15:50:05","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1279036,"visible":true,"origin":"","legend":"\u003cp\u003eTypical SEM images of a) as welded and b) PWHT samples, with 20% Cu donor material assisted FSW at a rotational rate of 1400 rpm and a welding speed of 1 mm/s.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/bc901e85aa8f958bded074ba.jpeg"},{"id":35048649,"identity":"81d801cc-1f8c-4c5d-a5c3-29d5da99e876","added_by":"auto","created_at":"2023-03-30 15:34:05","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1272458,"visible":true,"origin":"","legend":"\u003cp\u003e(a) and (b) SEM EDS images of the 20 and 60% solution treated (ST). (c) and (d) 20 and 60% 6 hours heat treated (HT) taken at the SZ.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/45ef753a6bf61bb029fbff6d.jpeg"},{"id":35048644,"identity":"08608a6c-fb7e-4ab4-8883-dc9643b4e098","added_by":"auto","created_at":"2023-03-30 15:34:05","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":286891,"visible":true,"origin":"","legend":"\u003cp\u003eEDS plot of FSW samples with 20% and 60% Cu ST and 6 hours HT\u003c/p\u003e\n\u003cp\u003esamples at SZ (Left) and BM(Right) respectively.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/1e7556e9d43b09d1a76ac20d.jpeg"},{"id":35049802,"identity":"c67e28ef-3a66-4d4d-8890-e206a47db7b1","added_by":"auto","created_at":"2023-03-30 15:42:05","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":448283,"visible":true,"origin":"","legend":"\u003cp\u003eNanoindentation at the SZ of FSW 20% Cu 6 hours HT sample (left).\u003c/p\u003e\n\u003cp\u003eEDS line spectrum of 20 points along the\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/02cef4a004d08253c0291a18.png"},{"id":35049798,"identity":"f1abf659-d7c0-426b-9560-b4f0450d00e6","added_by":"auto","created_at":"2023-03-30 15:42:05","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":854264,"visible":true,"origin":"","legend":"\u003cp\u003eXRD Spectra of the AA6066-T6 FSW samples under different heat\u003c/p\u003e\n\u003cp\u003etreatment conditions and Chemical Structure\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/ca5e575bca7d4009b7721a9b.jpeg"},{"id":35049799,"identity":"c3cc9f60-9b8c-4417-bc69-9f3c7e95e488","added_by":"auto","created_at":"2023-03-30 15:42:05","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":298639,"visible":true,"origin":"","legend":"\u003cp\u003eThe FSW Samples Phases Composition\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/059b94b5ea6282fe6665452b.png"},{"id":35049800,"identity":"967da4fe-a614-42ea-850d-27074957ca15","added_by":"auto","created_at":"2023-03-30 15:42:05","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":860671,"visible":true,"origin":"","legend":"\u003cp\u003eNanoindentation hardness versus depth of indentation in the BM (left) SZ (middle), and BM (right) of the 20% Cu 6 HT AW sample.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/b8300f6643ff26ff9598b716.jpeg"},{"id":35048653,"identity":"9248fb91-9bae-49b1-a391-6cb88b8fa40f","added_by":"auto","created_at":"2023-03-30 15:34:05","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2739211,"visible":true,"origin":"","legend":"\u003cp\u003eTypical tensile-tested fracture surface images of PWHTed samples with 20% Cu donor material at a rotational rate of 1400 rpm and a welding speed of 1 mm/s. (a and b) 20% Cu as-welded, (c and d) ST+AA 0 Hr.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/efd6de5d0308d657de5189a4.jpeg"},{"id":35048651,"identity":"775f0747-049e-4d5b-bc6e-a225f20bdc81","added_by":"auto","created_at":"2023-03-30 15:34:05","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1501689,"visible":true,"origin":"","legend":"\u003cp\u003eTypical tensile tested fracture surface images of PWHTed samples with 20% Cu donor material at a rotational rate of 1400 rpm and a welding speed of 1 mm/s. (a and b) ST+AA 6 Hr welded\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/ed8f64abe5de5f885f2f8a94.jpeg"},{"id":44699938,"identity":"1346d22a-870c-49c8-85ef-2d5292192a0f","added_by":"auto","created_at":"2023-10-16 15:09:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2752006,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2720330/v1/0d2a6dd8-3008-4172-98c6-5408722d364e.pdf"}],"financialInterests":"","formattedTitle":"Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eLightweight materials possess unique properties that are of great interest to DoD industries. Aluminum alloys (AA) represent lightweight materials used in various military applications due to their high strength-to-weight ratio and low fabrication cost compared to steel, titanium, and magnesium alloys. Aluminum alloys AA5083, AA2139, and AA7039 are often used in armored vehicles and military vessels [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These alloys meet the military standards for projectile resistance, corrosion resistance, lightweight, and weldability. Ballistic and armor-piercing tests are commonly performed on aluminum armored plates to ensure the strength and safety requirements are met for military applications. Although these alloys are used in armored vehicles, the complexity in manufacturability and sustainment of selecting appropriate aluminum alloys for vehicles' hull structures increased due to the lack of sufficient and efficient welding techniques. These aluminum alloys perform poorly in conventional fusion welding. FSW, a solid-state welding process, emerged as a promising alternative for welding aluminum alloys and overcoming defects such as porosities, solidification cracking, high residual stress, etc., generally associated with fusion welding[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. FSW produces low-cost quality welds compared with other welding processes. However, the loss of strength due to heat generation at the weld zone during welding is still a major concern [\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. For example, for gas metal arc welded (GMAWed) of AA2139-T8 alloys, weld strength, and elastic elongation, which are measures of the weld quality, are only 35\u0026ndash;55% of the base material.\u003c/p\u003e \u003cp\u003eTo strengthen aluminum alloy weldments, a solution heat treatment followed by rapid water quenching is recommended [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. This solution heat treatment process results in a metallurgical structure within the alloy that enhances the strength of the weld [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The formation and distribution of precipitants depend on the solution treatment temperature and the artificial aging time levels. Si and Mg are the two major alloying elements of the 6000-aluminum series that are typically added in the proportions required for the formation of hardening precipitates of Mg\u003csub\u003e2\u003c/sub\u003eSi. Since Mg\u003csub\u003e2\u003c/sub\u003eSi constitutes the main precipitants of the 6000-aluminum alloy series, this results in making the 6000-aluminum alloy series heat treatable by solutionizing and artificial aging processes.\u003c/p\u003e \u003cp\u003eHeat treatment influences the internal microstructure and hence the mechanical properties of metals and alloys, including hardness, yield strength, ultimate tensile strength, and corrosion resistance. Metals and alloys can be processed using various heat treatment approaches, such as changing the solutionizing temperatures and using different aging time levels [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Several manufacturing industries follow ASTM B917 and ASTM B91 standards for precipitation hardening or the so-called \"T6 heat treatment\". T6 heat treatment involves a solution heat treatment at a temperature of 540\u0026deg;C with a residence duration between 6 to 12 hours, followed by artificial aging at 155\u0026deg;C between 3 to 5 hours [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Rosso and Actis suggested that solutionizing metals for 1 hour rather than 6 hours would yield significantly better tensile strength. They also concluded that further subjecting metals to 180\u0026deg;C for 4 hours using artificial aging would yield better mechanical properties [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Shivkumar et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] and Zhang et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] concluded that a solution heat treatment temperature of 540\u0026deg;C followed by the artificial aging time between 3\u0026ndash;5 hours at 155\u0026deg;C is sufficient to yield better hardness and strength. Cabibbo et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] studied the effect of post weld heat treatment (PWHT) on FSW of AA6056 alloy and reported a significant increase in the tensile strength due to the formation of high-density precipitation of Mg\u003csub\u003e2\u003c/sub\u003eSi. Jamshidi and Serajzadeh [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] also reported that artificial aging increased the hardness of the friction stir welded AA6061 alloy. Although the formation of fine recrystallized grains, the dissolution and growth of precipitates were noticed in the weld zone after FSW [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Aging resulted in the formation of hardening precipitates, which led to a full recovery of the mechanical properties. Previous studies indicated that post-artificial aging is necessary to produce sufficient strength and hardness at the weld zone of a friction stir processing of 6000 series aluminum alloys. Priya et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] investigated the PWHT on FSW AA6061-T6 and AA 2219-T6 alloys and concluded that their ultimate tensile strength was increased due to the presence of fine precipitated particles. Hu et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] performed PWHT of friction stir welded AA2024 alloys and noticed that their mechanical properties were not changed but enhanced the weld's elongation. Aydin et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] studied solution heat treatment followed by an aging process on friction stir welded AA2024-T6 alloy and reported that the mechanical properties were significantly enhanced at 190\u0026deg;C for 10h artificial aging compared to natural aging. Recently, Bhukya et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] reported the effects of using copper donor stir assisted material of FSW of AA6061‑T6 alloy on the microstructure and mechanical properties of the welded specimens but not on PWHT. The PWHT research work has been accomplished on regular FSW aluminum alloys. However, the effect of PWHT on Cu donor stir assisted FSW AA6061-T6 alloy has not yet been investigated. This study used various techniques to investigate the chemical, microstructure, and mechanical properties, including FE-SEM, XRD, SEM-EDS, optical microscopy, and nanoindentation. The samples were subjected to a solid solution heat treatment at 540\u0026deg;C for 1 hour, followed by artificial aging for 0 and 6 hours at 180\u0026deg;C.\u003c/p\u003e"},{"header":"2.0 Experimental Procedure","content":"\u003cp\u003eThe CDSA sample preparation is detailed in [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In this study, a base metal of extruded AA6061-T6 alloy sheets with dimensions of 304.8 mm (length)\u0026times;76.2 mm (width)\u0026times;6.35 mm (thickness) was used to fabricate the test coupons. Test coupons, with dimensions of 152.4 mm (length)\u0026times;76.2 mm (width), were sectioned from the as-received sheets, and the edges were milled along the length. A trough with dimensions of 63.5 mm (length)\u0026times;25.4 mm (width) was forged onto the workpieces for positioning the donor stir-assisted material. Before welding, the trough and the donor stir-assisted material were cut and shaped using a CNC mill. A CDSA with 20% and 60% of the AA6061-T6 alloy thickness were selected for the current investigation. Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e list the chemical composition and mechanical properties of the AA6061-T6 and Cu-110 alloys, respectively. FSW experiments were conducted in the position control mode, using a triangle tapered pin-type tool head made of H13 steel. More information about the FSW machine used in this study can be found in [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The joints were friction stir butt-welded at a translational welding speed of 1mm/s and a tool rotation of 1400 rpm.\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\u003eChemical composition of AL6061-T6 and Cu 110 alloys.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\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=\"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=\"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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAlloy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eZr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eOther\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA6061-T6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95\u0026ndash;98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.05\u0026ndash;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u0026ndash;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.01\u0026ndash;0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.8\u0026ndash;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.01\u0026ndash;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.001\u0026ndash;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.001\u0026ndash;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.001\u0026ndash;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.001\u0026ndash;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.001\u0026ndash;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCu 110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e99.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e0.005\u0026thinsp;\u0026minus;\u0026thinsp;0.004\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 \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMechanical properties of Cu 110 and Al6061-T6.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA6061-T6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCu 110\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRockwell Hardness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40\u0026ndash;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eYield strength MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e241\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e255\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUltimate strength MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e345\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThermal conductivity W/mK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e151\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e183\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMelting Point \u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e585\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1084\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\u003eThe influence of PWHT on the mechanical/structural properties was investigated by dividing the weldments into two groups: As-Welded (AW) and heat-treated (HT) samples. The heat treatment process involved solution heat treatment in the furnace at a temperature of 530\u0026deg;C for 1 hour, followed by immediate water quenching. The samples were then artificially aged inside the furnace at a temperature of 180\u0026deg;C for 0 and 6 hours. The heat-treated metallography samples were cold-mounted, ground, polished, and etched with Keller's reagent for approximately 120 seconds to reveal the grain structure. An Olympus optical microscopy with quantitative image analysis software was used for microstructure and macrostructure studies. The friction stir welded coupons were sectioned using a wire electrical discharge machine (WEDM) in the direction perpendicular to the welding direction (WD) to examine the microstructures in the weld cross-sections.\u003c/p\u003e \u003cp\u003eThe fractured surface of the friction stir welded samples were subsequently examined using a JEOL 6700 FE-SEM equipped with three-dimensional (3-D) fractographic analysis capacity.\u003c/p\u003e \u003cp\u003eIndentation experiments were conducted on the AW samples using a Nanoindenter XP with a high-load attachment for the XP head that could apply a load of up to 10 N. The standard XP head and high load attachment enabled experiments from the nano to the micro regime using a single Berkovich diamond indenter tip. The nanoindenter tip was calibrated using a standard fused silica standard. Each indentation was made using the standard NanoSuite XP continuous stiffness method (CSM) protocol with a maximum depth of 5um.\u003c/p\u003e"},{"header":"3.0 Results And Discussion","content":"\u003cdiv class=\"Section2\" id=\"Sec4\"\u003e\n \u003ch2\u003e3.1. Microstructure analysis\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e(a-c) shows the microstructure of the 20% CDSA, the 0, and 6 hours solution treated AA6061-T6 samples. The samples represent the SZ location. The microstructure in the SZ consists of grains with slightly uneven boundaries, perhaps resulting from the high plastic deformation during the FSW process and the dissolution of the strengthening particles commonly occurring in the T6-treated base plate.\u003c/p\u003e\n \u003cp\u003eSmall grains were formed, and the grain size increased with the solution treatment time, Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a-b). The FE-SEM of Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb depicts smaller dark particles of the PWHT sample. These particles were not present in the FE-SEM of the AW sample PWHT precipitated strengthening particles in the SZ, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e(a). The development of the small dark particles in the PWHT is attributed to the presence of the Mg\u003csub\u003e2\u003c/sub\u003eSi intermetallic contents [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. This type of particle development can generally be found in AA6061-T6 alloy when the alloy undergoes heat treatment followed by an artificial aging process. The precipitation microstructure of Mg\u003csub\u003e2\u003c/sub\u003eSi during aging for AA 6061-T6 alloys is well documented in the literature [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. The number of intermetallic particles increases with the increase of the aging time. Equiaxed grains with fine grain size were formed and increased with the increase of the time of aging for the PWHT.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec5\"\u003e\n \u003ch2\u003e3.2. SEM, EDS observations\u003c/h2\u003e\n \u003cp\u003eSEM-EDS was used to evaluate the impact of the CDSA on the FSW AA6061-T6 alloy samples. Examination of the chemical contents of the FSW AA6061-T6 alloy samples indicated the dominance of Al (parent material), whereas CDSA was somewhat detected. The tests were performed for the base metal BM (left region), BM (right region), and the SZ zone (middle region). Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows EDS plots of the 20% and 60% CDSA, solution treated (ST), and 6 hours heat treated (HT) FSW AA6061-T6 alloy samples taken at several points at the SZ. Figures \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (a) and (b) represent the 20% and 60% ST samples, while Figs. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (c) and (d) represent the 20% and 60% 6-hour HT samples. Tables \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e (a-d) list elements\u0026apos; composition percentages at each point referenced in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Al is the major element, while other elements such as C, Fe, Mg, Mn, O, and Si exist in a small percentage. It is evident from the EDS images and the listing of the chemical elements at the SZ that the absence of the Cu element of the CDSA material is anticipated. EDS plots of FSW samples with 20% and 60% CDSA ST and 6 hours CDSA HT samples at the SZ and BM regions are shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, respectively. The plot unequivocally depicts Al as the major element in all samples. Al was also found to be the major element in the SEM-EDS analysis performed for a nanoindentation imprint in the SZ, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e. As we reported, other elements also existed but in very small percentages.\u003c/p\u003e\n \u003ctable border=\"1\" id=\"Tab3\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\" style=\"text-align: left;\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp style=\"text-align: left;\"\u003e(a) Weight % of the elements for the 20% ST CDSA at the SZ\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLocation\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt1\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e73.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt2\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.96\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt3\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.84\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt4\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt5\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;20%(1)_pt6\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003ctable border=\"1\" id=\"Tab4\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\" style=\"text-align: left;\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp style=\"text-align: left;\"\u003e(b) Weight % of the elements for the 60% ST CDSA at the SZ\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLocation\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eC\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eO\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eMg\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eAl\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eSi\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eFe\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;60%(1)_pt1\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e68.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;60%(1)_pt2\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;60%(1)_pt3\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;60%(1)_pt4\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e79.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"BoldItalic\" name=\"Emphasis\" type=\"BoldItalic\"\u003eST-M\u0026nbsp;60%(1)_pt5\u003c/span\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eTable 3\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(c) Weight % of the elements for the 20% 6-hour HT CDSA at the SZ\u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eLocation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eF\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eMg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eAl\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eSi\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eMn\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003eFe\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;20%(1)_pt1\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e7.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e70.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e5.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e13.19\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;20%(1)_pt2\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e6.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e1.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e82.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e2.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e6.43\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;20%(1)_pt3\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e6.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e86.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e1.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e3.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;20%(1)_pt4\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e6.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e19.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e52.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e20.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;20%(1)_pt5\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e5.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e93.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003e0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"11.11111111111111%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eTable 3\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e(d) Weight % of the elements for the 60% 6-hour HT CDSA at the SZ\u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"1\" cellpadding=\"0\" cellspacing=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003eLocation\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eC\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eO\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eMg\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eAl\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eSi\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eK\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eFe\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;60%(1)_pt1\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e6.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e2.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e81.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e3.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e5.84\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;60%(1)_pt2\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e8.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e9.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e1.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e73.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e5.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e1.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;60%(1)_pt3\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e6.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e3.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e0.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e75.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e5.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e9.24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;60%(1)_pt4\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e11.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e13.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e65.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e7.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eHT6-M\u0026nbsp;60%(1)_pt5\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e6.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e2.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003e90.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" width=\"12.5%\"\u003e\n \u003cp\u003eND\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eND* - not detectable.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec6\"\u003e\n \u003ch2\u003e3.3. XRD analysis\u003c/h2\u003e\n \u003cp\u003eThe XRD results are presented in the plot of Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The plot includes 20%, 60% DCSA zero hours ST, 6 hours HT, and BM samples. In addition to the presence of Al at several peaks [\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2{\\theta }(^\\circ )=37.50, 64.07, 77.32, and 81.55]\\)\u003c/span\u003e\u003c/span\u003e, other elements such Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Mg\u003csub\u003e2\u003c/sub\u003eSi, Al\u003csub\u003e8\u003c/sub\u003eFe\u003csub\u003e2\u003c/sub\u003eSi, Al(FeMnCr)Si, and Al+Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e existed with smaller amounts at peaks of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2{\\theta }\\left(^\\circ \\right)=36.14, 39.54, 41.56, 42.35 and 43.51,\\)\u003c/span\u003e\u003c/span\u003e respectively.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e shows the XRD patterns of the 20%, 60% DCSA zero hours ST, 6 hours HT, and BM samples. Again, the diffraction peaks are labeled in the Figure. It is also observed that the samples depicted aluminum cubic and Al, Fe, and Si systems of hexagonal crystal structure.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003e3.5. Nanohardness measurements\u003c/h2\u003e\n \u003cp\u003eThe nanoindentation plot of Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e indicated the softening effect in SZ of the 20% Cu 6 hours heat treated samples. The hardness at the SZ was measured as 0.55 GPa compared to a hardness of 0.63 GPa for the BM fat, with a depth of indentation of 4.75 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\mu m\\)\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e3.6. Fractography\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e (a-d) and Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e (a-b) show fracture surfaces of the 1400 rpm and 1 mm/s of as welded and 6 hours heat treated samples. These fractographic images include crack initiation, spherical and broken dimples, secondary cracks, tear ridges, and particles. It is noted that crack initiation occurs in the vicinity of the TMAZ/HAZ retreating side following the PWHT, Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003ea. The fracture surface presents many small spherical dimples with layered distribution, which often indicates a ductile fracture. The 20% CDSA AW samples exhibited intergranular cracking with coarser dimples. The dimples were becoming finer for the PWHT welded samples, and the emerging grains were getting smaller than the AW\u0026apos;s grain when the aging time was increased, Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003eb.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e3.7. Conclusions\u003c/h2\u003e\n \u003cp\u003eThe present research aims to investigate the microstructure, crystal structure, chemical composition, and mechanical properties of the welded joints of 20% and 60% CDSA PWHT samples. Optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation techniques were utilized. The results are as follows:\u003c/p\u003e\n \u003col\u003e\n \u003cli\u003e\n \u003cp\u003eThe SZ and the TMAZ, predominantly composed of equiaxed grains, experienced complete dynamic recrystallization. The grain size in the SZ became finer after PWHT, followed by 6 hours artificial aging process. A significant amount of strengthening intermetallic particles of Mg\u003csub\u003e2\u003c/sub\u003eSi was observed after PWHT, which changed the structure of the AA6061-T6 alloy.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eAfter the PWHT, there was a sudden increase in the hardness at the center of the weld. The SZ is softer than the BM from the nanoindentation hardness results.\u003c/p\u003e\n \u003c/li\u003e\n \u003cli\u003e\n \u003cp\u003eFractography of the AW tensile testing fractured samples exhibited intergranular cracking with large dimples. The fractured surface for the PWHT samples exhibited a ductile-like fracture with a large number of fine dimples. These dimples emerged in the ductile fractured surfaces, which only correspond to voids. For the PWHT joint, the dimples were becoming finer, and the grains that emerged were smaller than the AW when the aging time was increased.\u003c/p\u003e\u003cbr\u003e\n \u003c/li\u003e\n \u003c/ol\u003e\n\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e1. What is your main contribution to the field?\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe primary contribution of this research, entitled \u0026quot;Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Cu Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy,\u0026quot; is the analysis of the effects of post weld heat treatment on the microstructure, crystal structure, chemical composition, and mechanical properties of AA6061-T6 alloy welded joints produced using Cu donor stir assisted friction stir welding. In this research, we concluded that the stir zone exhibited grain refinement after the heat treatment and artificial aging process, which led to the formation of strengthening intermetallic particles of Mg\u003csub\u003e2\u003c/sub\u003eSi. In addition, nanoindentation test results showed that the hardness results\u0026nbsp;of the base metal (BM), which is represented by the left and right regions are consistent with the hardness of the AA6061-T6 hardness results. Furthermore,\u0026nbsp;the stir zone experienced softening as compared to the base metal. These findings offer important insights and guidelines for optimizing welding processes and post-weld heat treatments to enhance the performance and durability of welded structures made from the AA6061-T6 alloy.\u003c/p\u003e\n\u003cp\u003e2. \u003cstrong\u003eWhat is novel? In theory, in experimental techniques, or a combination of both?\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn our research on \u0026quot;Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Cu Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy,\u0026quot; The novelty lies in using high characterization techniques to identify post weld heat treatment and how it impacts the crystal structure, microstructure, chemical composition, and mechanical properties of the welded AA6061-T6 joints.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur research revealed that the stir zone exhibited grain refinement after the heat treatment and artificial aging process, leading to the formation of strengthening intermetallic particles of Mg\u003csub\u003e2\u003c/sub\u003eSi.\u0026nbsp;We measured the hardness of the base metal (BM), left and right regions as\u0026nbsp;~\u0026nbsp;6.5 GPa, whereas at the SZ, the hardness is\u0026nbsp;~\u0026nbsp;5.5 GPa at a depth of indentation of 4.7 \u0026micro;m.\u003c/p\u003e\n\u003cp\u003e3. \u003cstrong\u003eDoes your paper have industrial applications? If yes, who are the likely user?\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe research findings and recommendations could be advantageous to industries such as transportation, aviation, maritime, and civil engineering by providing insights to enhance welding processes and post-weld heat treatment procedures. This, in turn, could contribute to the improvement of performance and longevity of welded joints made from AA6061-T6 and other alloys. As a result, the intended users of this research include materials engineers, industrial specialists, and fabrication professionals working across these various sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors express their gratitude for the funding support from NASA (grant ID: 80NSSC20M0015). ZW appreciates the support from ONR (grant ID: N00014-19-1-2728). This document\u0026apos;s perspectives, discoveries, deductions, or suggestions belong to the author(s) and do not necessarily represent NASA and ONR\u0026apos;s viewpoints. The authors acknowledge the Commonwealth Center for Advanced Manufacturing (CCAM) and Amsted Rail for making available the infrastructure required for specimen evaluation. Finally, the valuable contribution of Mr. Geoff Widman in carrying out the experiments is acknowledged and appreciated.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea. Funding:\u0026nbsp;\u003c/strong\u003eThe authors would like to acknowledge support from NASA (award number: 80NSSC20M0015). The author ZW also acknowledges support from ONR (award number: N00014-19-1-2728). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NASA and ONR.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb. Competing Interests\u003c/strong\u003e:\u0026nbsp;The authors have no relevant financial/non-financial interest neither conflict of interest to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec. Author Contributions:\u0026nbsp;\u003c/strong\u003eMr. A. H. Al-Allaq performed XRD characterization and wrote/revised the manuscript. \u0026nbsp;Dr. S. Bhukya carried out experimentation and data analysis for the CDSA and revised the manuscript. Dr. A.A. Elmustafa conceptualized the research and wrote/revised the manuscript. Dr. Z. Wu secured the funding. Mr.\u003csup\u003e\u0026nbsp;\u003c/sup\u003eM. Ojha performed the SEM-EDS and Dr. Y. Mohammed performed the nanoindentation testing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eGrujicic M, Arakere G, Pandurangan B, et al (2011) Development of a Robust and Cost-Effective Friction Stir Welding Process for Use in Advanced Military Vehicles. J Mater Eng Perform 20:11\u0026ndash;23. https://doi.org/10.1007/s11665-010-9650-0\u003c/li\u003e\n\u003cli\u003eThomas WM, Nicholas ED, Needham JC, et al. (1995) Friction welding\u003c/li\u003e\n\u003cli\u003eKallee SW, Nicholas D (2006) Friction stir welding at TWI. The Welding Institute (TWI): Cambridge, England\u003c/li\u003e\n\u003cli\u003eThomas WM, Dolby RE (2003) Friction stir welding developments. Proceedings of the sixth international trends in welding research 203\u0026ndash;211\u003c/li\u003e\n\u003cli\u003eJata K v., Semiatin SL (2000) Continuous dynamic recrystallization during friction stir welding of high strength aluminum alloys. Scr Mater 43:743\u0026ndash;749. https://doi.org/10.1016/S1359-6462(00)00480-2\u003c/li\u003e\n\u003cli\u003eLakshminarayanan ak, Balasubramanian V (2008) Process parameters optimization for friction stir welding of RDE-40 aluminum alloy using Taguchi technique. Transactions of Nonferrous Metals Society of China 18:548\u0026ndash;554. https://doi.org/10.1016/S1003-6326(08)60096-5\u003c/li\u003e\n\u003cli\u003eValery IR, Don L, Raymond C (2002) Handbook of Induction Heating: Manufacturing Engineering and Materials Processing\u003c/li\u003e\n\u003cli\u003eDavis JR (1993) Aluminum and aluminum alloys. ASM International\u003c/li\u003e\n\u003cli\u003eMenargues S, Mart\u0026iacute;n E, Baile MT, Picas JA (2015) New short T6 heat treatments for aluminum silicon alloys obtained by semisolid forming. Materials Science and Engineering: A 621:236\u0026ndash;242\u003c/li\u003e\n\u003cli\u003eRosso M, Actis Grande M (2006) Optimization of heat treatment cycles for automotive parts produced by rheocasting process. In: Solid State Phenomena. Trans Tech Publ, pp 505\u0026ndash;508\u003c/li\u003e\n\u003cli\u003eShivkumar S, Ricci S, Steenhoff B, et al. (1989) An experimental study to optimize the heat treatment of A356 alloy. AFS Transactions 97:791\u0026ndash;810\u003c/li\u003e\n\u003cli\u003eZhang DL, Zheng LJ (1996) The quench sensitivity of cast Al-7 wt pct Si-0.4 wt pct Mg alloy. Metallurgical and Materials Transactions A 27:3983\u0026ndash;3991\u003c/li\u003e\n\u003cli\u003eCabibbo M, McQueen HJ, Evangelista E, et al. (2007) Microstructure and mechanical property studies of AA6056 friction stir welded plate. Materials Science and Engineering: A 460\u0026ndash;461:86\u0026ndash;94. https://doi.org/https://doi.org/10.1016/j.msea.2007.01.022\u003c/li\u003e\n\u003cli\u003eJamshidi Aval H, Serajzadeh S (2014) A study on natural aging behavior and mechanical properties of friction stir-welded AA6061-T6 plates. The International Journal of Advanced Manufacturing Technology 71:933\u0026ndash;941. https://doi.org/10.1007/s00170-013-5531-7\u003c/li\u003e\n\u003cli\u003ePriya R, Subramanya Sarma V, Prasad Rao K (2009) Effect of post weld heat treatment on the microstructure and tensile properties of dissimilar friction stir welded AA 2219 and AA 6061 alloys. Transactions of the Indian Institute of Metals 62:11\u0026ndash;19. https://doi.org/10.1007/s12666-009-0002-4\u003c/li\u003e\n\u003cli\u003eHu Z, Yuan S, Wang X, et al. (2011) Effect of post-weld heat treatment on the microstructure and plastic deformation behavior of friction stir welded 2024. Mater Des 32:5055\u0026ndash;5060. https://doi.org/https://doi.org/10.1016/j.matdes.2011.05.035\u003c/li\u003e\n\u003cli\u003eAydın H, Bayram A, Durgun İ (2010) The effect of post-weld heat treatment on the mechanical properties of 2024-T4 friction stir-welded joints. Materials \u0026amp; Design (1980-2015) 31:2568\u0026ndash;2577. https://doi.org/https://doi.org/10.1016/j.matdes.2009.11.030\u003c/li\u003e\n\u003cli\u003eBhukya SN, Wu Z, Maniscalco J, Elmustafa A (2022) Effect of copper donor material-assisted friction stir welding of AA6061-T6 alloy on downward force, microstructure, and mechanical properties. The International Journal of Advanced Manufacturing Technology 119:2847\u0026ndash;2862. https://doi.org/10.1007/s00170-021-08390-8\u003c/li\u003e\n\u003cli\u003eASTM Standard Test Methods for Tension Testing of Metallic Materials, ASTM E8\u003c/li\u003e\n\u003cli\u003eKhalili V, Heidarzadeh A, Moslemi S, Fathyunes L (2020) Production of Al6061 matrix composites with ZrO2 ceramic reinforcement using a low-cost stir casting technique: Microstructure, mechanical properties, and electrochemical behavior. Journal of Materials Research and Technology 9:15072\u0026ndash;15086. https://doi.org/10.1016/J.JMRT.2020.10.095\u003c/li\u003e\n\u003cli\u003eKhalil O, Mingareev I, Bonhoff T, et al. (2014) Studying the effect of zeolite inclusion in aluminum alloy on measurement of its surface hardness using laser-induced breakdown spectroscopy technique. Optical Engineering 53:014106. https://doi.org/10.1117/1.OE.53.1.014106\u003c/li\u003e\n\u003cli\u003eWoo W, Ung\u0026aacute;r T, Feng Z, et al. (2010) X-Ray and Neutron Diffraction Measurements of Dislocation Density and Subgrain Size in a Friction-Stir-Welded Aluminum Alloy. Metallurgical and Materials Transactions A 41:1210\u0026ndash;1216. https://doi.org/10.1007/s11661-009-9963-5\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Friction stir welding, Micro-structured/surface characterization, Heat treatment processes","lastPublishedDoi":"10.21203/rs.3.rs-2720330/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2720330/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePost weld heat treated AA6061-T6 alloy resulted from the application of a Cu donor stir assisted (CDSA) friction stir welding (FSW) material was examined for crystal structure and mechanical properties. CDSA FSW samples were tested at a constant tool rotational speed of 1400 rpm and a welding translational speed of 1 mm/s. CDSA samples of 20% and 60% thickness of the AA6061-T6 base alloy were selected to assist the FSW joining at the plunge stage. The FSW AA6061-T6 samples were solid solution treated at 540 °C for one hour, followed by quenching in water at room temperature. The samples were then artificially aged at 180 °C for 6 hours, respectively, followed by air cooling. The samples were tested for microstructure, crystal structure, chemical composition, and mechanical properties using optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation. The microstructure shows the additional grain refinement in the stir zone (SZ) due to recovery and recrystallization with increasing aging time. Examination of the chemical contents of the FSW AA6061-T6 alloy samples using scanning electron microscopy with energy dispersive spectroscopy (EDS) revealed Al (parent material) as the predominant element, while Cu (CDSA) was minimally present as expected. XRD results of the CDSA FSW samples depicted crystal orientations similar to the orientations of the AA6061-T6 alloy. Nanoindentation tests revealed softening effects due to the dissolution of hardening precipitates at the SZ. The hardness of the base metal (BM), left and right regions, is reported as ~ 6.5 GPa, whereas at the SZ, the hardness is ~ 5.5 GPa at a depth of indentation of 4.7 µm.\u003c/p\u003e","manuscriptTitle":"Post Weld Heat Treatment Effects on Microstructure, Crystal Structure, and Mechanical Properties of Donor Stir Assisted Friction Stir Welding Material of AA6061-T6 Alloy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-03-30 15:34:00","doi":"10.21203/rs.3.rs-2720330/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2023-04-20T14:13:26+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2023-03-29T00:11:54+00:00","index":0,"fulltext":""},{"type":"editorAssigned","content":"","date":"2023-03-27T08:29:23+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2023-03-24T10:34:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"58038186-9e2f-4389-bb95-5bb6eee16bc0","owner":[],"postedDate":"March 30th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T15:05:57+00:00","versionOfRecord":{"articleIdentity":"rs-2720330","link":"https://doi.org/10.1007/s00170-023-12407-9","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2023-10-10 15:02:33","publishedOnDateReadable":"October 10th, 2023"},"versionCreatedAt":"2023-03-30 15:34:00","video":"","vorDoi":"10.1007/s00170-023-12407-9","vorDoiUrl":"https://doi.org/10.1007/s00170-023-12407-9","workflowStages":[]},"version":"v1","identity":"rs-2720330","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2720330","identity":"rs-2720330","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}