Retrogression and Reaging – Aluminum Alloy AA7012

Retrogression and Reaging – Aluminum Alloy AA7012 | 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 Retrogression and Reaging – Aluminum Alloy AA7012 Luiz Rosa, André Luís Moreira de Carvalho, Luis Rogerio de Oliveira Hein, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5389427/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Apr, 2025 Read the published version in Journal of Materials Science: Materials in Engineering → Version 1 posted You are reading this latest preprint version Abstract Retrogression and Reaging (RRA) is of interest to the automotive industry for manufacturing components of high-strength aluminum alloys. This study describes obtaining the Retrogression and Reaging curve for the aluminum alloy AA7012-T6 (Al-Zn-Mg-Cu) – UNS A97012. The RRA heat treatment consists of two stages: the first stage is retrogression, which was carried out on the samples in the T6 hardening condition for a time ranging from 5 seconds to 4 hours and at different temperatures: 180°C, 210°C, and 240°C. The second stage, re-aging, was conducted at 120°C for 24 hours (process parameters for obtaining the T6 temper). The RRA curve was obtained by measuring hardness Vickers (HV). The samples were also evaluated for electrical conductivity (%IACS - International Annealed Copper Standard ). The best response for the RRA curve was obtained with retrogression at 180°C/1h and re-aging at 120°C for 24 hours. The increase in hardness (HV) obtained with RRA 180°C/1h and reaged at 120°C/24h was 19%. Aluminum Alloy Retrogression Reaging AA7012 Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 1. Introduction The challenge for the 21 st century, in the development of aeronautical and automotive products, is the conjunction between the value paid for the product and the environmental impact caused by the manufacturing process of that product. Aluminum and its alloys meet the requirement of low value for money when the ratio of mechanical properties to component mass is considered. The extraction and processing of aluminum have an environmental impact, but this impact can be reduced by recycling [1]. High-strength aluminum alloys are of interest to the automotive industry because of their potential to reduce the mass of components. Generally, high-strength alloys have high Yield and Strength limits, 500 and 570 MPa, respectively, and a low density compared to steel, 2.8 g/cm 3 versus 7.7 g/cm 3 [2]. The the good corrosion resistance, excellent workability, high ratio of mechanical strength to density, and appropriate electrical and heat conductivity, classify aluminum alloys for the manufacture of industrial components and automotive components such as pistons, steering gears, engine blocks, wheels [3], and also pumpers. These components potentially can be made with AA7012 by applying the RRA heat treatment. All of these factors make aluminum alloys attractive to the automotive industry. The Retrogression and Reaging (RRA) heat treatment was introduced by Cina and his colleagues, in Israel, in the early 1970s, to improve the mechanical strength and stress corrosion cracking of AA 7075-T6, using temperatures between 200°C and 280°C and time from 1 to 30 seconds with material 2.8 mm thick [4] and [5]. Since 1980, LAR-NCR (Institute for Aerospace Research, National Research Council of Canada) has been working on the development of retrogression and reaging heat treatment technology with material up to 6.35mm thick [5]. The RRA is a two-stage heat treatment that improves the mechanical properties and stress corrosion resistance (SCC) of 7xxx series aluminum alloys. The alloy to be treated must be at T6 temper, the first stage is retrogression made to a temperature between the aging temperature and the solubilization, and the second stage is the artificial reaging - identical to the parameters to obtain T6 temper, generally 120°C for 24 hours. The schematic diagram used in this study is shown in Figure 1, including solubilization, aging, retrogression, and reaging. This study aims to determine the RRA curve for AA7012 (Al-Zn-Mg-Cu-Zr), as well as the respective process parameters. This is of interest to the automotive industry. The use of lighter materials with adequate mechanical strength has become a constant request for vehicle manufacturers. Gears, axles, and bumpers are potential components to be manufactured with AA7012 applying the RRA heat treatment. The AA7012 alloy is characterized by a Zn/Mg (mass) ratio of approximately 3, a copper content of around 1% by mass, and the presence of zirconium and manganese replacing chromium as dispersoid-forming elements. The chemical composition of the AA7012 alloy is characterized by the following parameters: i) The iron and silicon contents are reduced to the maximum permitted values, % by mass, of 0.25% and 0.15% respectively. The concentrations of α-AlFeSi, Al 7 Cu 2 Fe, Mg 2 Si, and (Fe,Cu,Mn)Al 6 are reduced, increasing the toughness value. Iron and silicon drag down magnesium and copper, reducing their contribution to age hardening. The chemical composition of the AA7012 alloy is shown in Table 1 [7] and [8]. ii) Zirconium, in a controlled percentage, replaces chromium to control recrystallization, forming the Al 3 Zr dispersoid. The removal of chromium eliminates the formation of Al 18 Cr 6 Mg 2 , which removes magnesium from the alloy, thus reducing its hardening effect on aging. iii) The percentage by mass of zinc is not less than 5.8% and the minimum percentage of copper and magnesium is 0.8% and 1.8% (by mass) respectively. iv) Presence of titanium and manganese in controlled percentages. v) The AA7012 is less sensitive to quench rate when compared with AA7075. The chemical composition of the AA7012 aluminum alloy is shown in Table 1 [6]. Table 1. Chemical Composition AA7012 (mass %) – [6] AA7012 Zn Mg Cu Ti Si Fe Mn Cr Zr Specification 5.8 –6.5 1.8 – 2.2 0.8 – 1.2 0.02 – 0.08 0.15 max 0.25 max 0.08 – 0.15 0.04 max 0.10 – 0.18 Due to the high solubility of zinc (82.8% - mass) and magnesium (14.9% - mass) in solid aluminum [7], the mechanical properties of 7xxx series alloys can be significantly increased through solubilization heat treatment and artificial aging. The increase in hardness and mechanical properties is due to the precipitates formed in the microstructure and obstructing the movement of dislocations [8]. The Liquidus and Solidus temperatures of AA7012 are 636°C and 475°C respectively [9]. The precipitation hardening induced by artificial aging of the 7xxx series aluminum alloys and accepted for the AA7012 alloy is described in Equation 1 [10] and [11]: where: a) Al αsss is the supersaturated solid solution of aluminum that is retained after cooling, usually in water. b) G-P zones are the Guinier and Preston I and II zones. c) Precipitate η': metastable phase, MgZn 2 . d) Precipitate η: equilibrium phase, MgZn 2 . During aging there is fine precipitation of the G-P Zones inside the grains, and as a consequence, there is an increase in the hardness of the alloy [12] and [13]. Buha and his colleagues [13] indicate the formation of two types of G-P Zones: 1) G-P I zones, exhibit a spherical morphology, composed of ordered and coherent layers of Zn and Mg/Al atoms on {111} Al . 2) G-P II zones, exhibit a platelet morphology composed of layers of zinc in {111} Al . G-P II Zones form after cooling from 450°C and when aged above 70°C. On T6 temper, the aluminum alloy 7012 has a minimum Tensile (0.2%) Strength and minimum Yield Strength of 560 MPa and 520 MPa respectively, and a minimum elongation (50 mm) of 6% [9]. The typical curve resulting from RRA heat treatment (time versus hardness is shown in Figure 2 [14], [15], [16] and [17]. During retrogression, the hardness initially decreases to a minimum value until the retrogression time (TR) - Zone I, this is caused by the dissolution of the G-P and/or η' Zones formed during aging. After the TR the hardness increases again to a local maximum value - Zone II, this increase in hardness is associated with the growth of the η' phase and precipitation of the η phase [18]. After reaching the maximum local hardness there is a reduction in hardness values due to the over-aging of the alloy. The slight recovery of hardness after TR is due to the precipitation and growth of η precipitates [5]. When the time of the retrogression stage is short enough to allow only the dissolution of precipitates, the subsequent reaging at 120°C for 24 hours will bring the material back to maximum hardness [4]. The recommended retrogression time is identified by TR on Figure 2. If the alloy is retrogressed for a longer time than TR, the original hardness of the T6 hardening may not be recovered by subsequent reannealing because the solute elements agglomerate, preventing the formation of η' and η' precipitates. Feng et al. [18] indicate the occurrence of three main reactions during retrogression: 1) partial dissolution of the G-P Zones and the η' phase, which are responsible for the reduction in hardness observed in Zone I; 2) formation of growth of the η' phase, which is responsible for the increase in local hardness (Zone II), and 3) agglomeration of precipitates, which causes the reduction in hardness (Zone III). Ning et al. [19] studied the 7xxx series aluminum alloys, 6.28Zn-2.19Mg-1.6Cu-0.15Cr, solubilized at 470°C/1 hour; aged at 120°C/24h (T6 hardening) and retrograded at 200°C and reaged according to the parameters used in the T6 hardening, the retrogression time (TR) obtained was 6 minutes; for the alloy 9. 99Zn-2.5Mg-1.72Cu-0.13Zr alloy, solubilized at 450°C/2h plus 470°C/1h and retempered at 200°C and reaged according to the parameters used in the T6 tempering, the retrogression time (TR) obtained was 7 minutes. Different regression times were used for both alloys, ranging from 2 to 45 minutes. The shape of the RRA curve (HV hardness versus time in minutes) corresponds to that shown in Figure 2; there is no mention of the dimensions of the specimens used to determine the RRA curve. The aluminum alloy 9.99Zn-2.5%Mg-1.72%Cu-0.13 %Zr was also studied by Feng et al. [18], the study was carried out on samples aged at 100°C/24h (T6), retempered at 200°C/7 minutes and reaged. The samples were cylindrical, 12 mm in diameter. Park and Ardel [20] studied the AA7075 T651 alloy; the samples used to draw up the RRA curve were 0.25 mm thick. The retrogression was carried out in a salt bath at 240°C for various times up to 60 seconds and re-aged at 120°C/48h in an oil bath. The observed retorting time was 24 seconds. Ural [16] and Esmailian et al. [21] also studied the AA7075 alloy, in the first study the maximum hardness was obtained with a temperature and regression time of 200°C/40 minutes, after re-aging for 120°C/24h, in the second study, using a silicon bath, the conditions established for the RRA were 200°C / 45 - 60 minutes and re-aging at 120°C/24h, in the second study the samples were 25.4 mm thick. Crawford et al. [17] mention that using temperatures of around 180°C - 195°C prolongs the retrogression stage, making it easier to control the process. Experiments by the Institute of Aerospace Research (IAR) from Canada working with the aluminum alloy AA7075-T6511 controlled the RRA process by electrical conductivity. The better condition in terms of electrical conductivity was 38,5% IACS (International Annealed Cooper Standard [5]. Oliveira et al. [studied AA7050, 2.5 mm thick, for a retrogression time of 40 minutes and got values of 36 – 39 % IACS, the maximum value was for an aging time of 1000 minutes. 2. Materials and Methods The material used in this study was supplied by ALCOA - Brazil as an extruded AA7012 aluminum bar (15 mm diameter and 700 mm long). The AA7012 alloy was produced by the direct extrusion process, homogenized, and supplied as manufactured. The nominal composition is shown in Table 2. Table 2. Chemical Composition AA7012 (mass %) AA7012 Zn Mg Cu Ti Si Fe Mn Cr Zr Sample RRA 5.99 1.96 0.94 0.04 0.09 0.13 0.12 0,002 0.13 Note: The Zn/Mg ratio for the sample under study is 3.05. The solubilization heat treatment was carried out on 150 mm bars. The bars were cut with a hand saw and solubilized at 465°C for 2 hours in an EDG 7000/FDG 3P-S furnace, and cooled in water at 25°C with moderate stirring. The aging process was carried out in an EDG 7000/FDG 3P-S furnace, Ø 15mm and 30 mm long specimens were used for artificial aging, which was carried out at 120°C for 24 hours, cooled in still air. Three different temperatures of 180°C, 210°C and 240°C were used for the retrogression, with step times of 5s, 10s, 15s, 20s, 30s, 1min, 5min, 15min, 30min, 60min, 120min, 180min and 240 min. Retrogression was carried out in a salt bath using AS 140 salt by HEF™ DURFERRIT, Figure 3. After regression, the samples were washed in running water with neutral soap. Re-aging was carried out in an EDG 7000/FDG 3P-S oven at 120°C for 24 hours, cooled in still air. The metallographic preparation was carried out in four stages: 1) Cutting: TECHCUT 4 automatic saw - ALLIED - HIGH TECH PRODUCTS, INC. with a diamond disk at 200rpm. 2) Embedding: AROTEC hydraulic press and bakelite. 3) Sanding: METPREP 3, PH - 3 automatic polishing machine, using water as a lubricant and sandpaper of 320, 400, 600, 800, 1200, 2000 and 2400 (mesh). 4) Polishing: VIBRATORY POLISHER, PACE TECHNOLOGIES, GIGA - 0900, silica 0.02µm (50%) for 24 hours. Microstructural analysis was carried out considering the number of preciptates and their morphology and size. The following parameters were used for morphological analysis: Circularity (C) , Solidity (SOL) and Aspect Ratio (AR), for dimensional analysis the Feret Diameter was used. This analysis was carried out using a Zeiss AxioImager Z2m optical microscope. The analysis macro was created using ImageJ software (Image Processing and Analysis in Java [20]. A total of 121 regions were analyzed. ImageJ Routine is shown on Annex I. Scanning Electron Microscopy (SEM) analysis was carried out using the Zeiss EVO LS 15 SEM electron microscope and EDS (Energy Dispersive Spectroscopy) Oxford Instruments Xplore 30. Circularity is defined as C = 4.π. Area / Perimeter 2 , it is a dimensionless number defined in the interval (0,1], Solidity (SOL) is defined as the ratio between Area / Convex Area, it is a dimensionless number defined in the interval (0,1]. Aspect Ratio (AR) is defined as the ratio between width (L) and height (h). The Feret diameter is defined as the maximum distance between two parallel, tangent points on opposite sides of the image of a randomly oriented particle. The Vickers hardness measurement (HV) was evaluated at half the radius of the samples (diameter 15 mm) in a Wilson Instruments Model 401 MDV microhardness tester using a 500-gram rod with a penetration time of 15 seconds. The hardness assessment was carried out at room temperature. To measure electrical conductivity, the samples were stabilized at 20°C for 24 hours. A portable SIGNASCOPE® Fisher SERIAL 4502 conductivity meter and a 14mm diameter probe was used. The results were given in percentage according to the International Annealed Copper Standard (IACS). 3. Results The RRA curves obtained for 180°C, 210°C and 240°C retrogression, both re-aged at 120°C / 24h are illustrated in figures 5, 6 and 7 respectively. The hardness in the T6 condition was 184HV. Only the material retrogressed at 180°C/1h and reaged at 120°C/24h have a significante increse on hardnesss, i.e., from 160 HV to 220 HV, an increase of 37.5% and comparing with T6 original hardness (184 HV) and incresse of 19.5% was observed. The morphology of the precipitates were analyzed for the conditions that showed retrogressed at 180°C: i) sample reaged for 15 seconds (within Zone I), 1 hour (within Zone II - TR) and 2 hours (within Zone 3). The morphology of the precipitates is shown in Figures 8, 9 and 10. The results of the morphological and dimensional analysis are shown in Tables 3, 4 and 5. Table 3. Retrogression:180°C/15seconds – Reaging:210°C/ 24h Circularity Feret Diameter (µm) Aspect Ratio (AR) Solidity (Sol) Average 0.88 1.55 1.40 0.89 Std. Deviation 0.07 0.70 0.27 0.03 Min 0.71 0.47 1.00 0.69 Max 0.99 7.68 3.01 1.00 Precipitate 72918 Table 4 . Retrogression:180°C/1h – Reaging:210°C/24h Circularity Feret Diameter (µm) Aspect Ratio (AR) Solidity (Sol) Average 0.88 1.35 1.33 0.88 Std. Deviation 0.07 0.56 0.25 0.04 Min 0.71 0.47 1.00 0.65 Max 0.99 11.11 3.50 1.00 Precipitate 103313 Table 5. Retrogression:180°C/ 2h – Reaging:210°C/ 24h Circularity Feret Diameter (µm) Aspect Ratio (AR) Solidity (Sol) Average 0.87 1.26 1.32 0.87 Std. Deviation 0.07 0.53 0.25 0.04 Min 0.71 0.47 1.00 0.63 Max 0.99 7.37 3.50 Precipitate 95073 The quantity of precipitates are indicated in Figure 11 for Retrogression at 180°C and reaged at 120°C/24h. The results of measured electrical conductivity, are indicated in Figure 12 to Retrogression at 180°C, 210°C e 240°C, reaging at 120°C/24h. The SEM of the precipitates were analyzed for the conditions that showed retrogressed at 180°C: i) sample reaged for 15 seconds (within Zone I), 1 hour (within Zone II - TR) and 2 hours (within Zone 3). The morphology of the precipitates is shown in Figures 13, 14 and 15. 4. Discussion There is a large discrepancy in retrogression treatment time (TR) between the authors consulted. The main cause is the variation in the thickness of the specimens used in the studies, i.e. from 0.25 mm to 25.4 mm and the aluminum alloy used on the study. The retrogression temperatures reported were always higher than the aging temperature and lower than the solubilization temperature. Ning et al. [19] studied a 7xxx series (6.28Zn-2.19Mg-1.6Cu-0.15Cr) that got retrogression process parameters of 200°C/7 minutes, no reference to the specimen thickness was reported in their study. Park and Ardel [20] for the AA7075 got a retrogression parameter of 240°C/25 seconds for thin samples cut in strips of 0.25mm in thickness. Feng et al. [18] got retrogression parameters of 200°C/7minutes studying the alloy Al-9.99Zn-1.72%Cu-2.5%Mg-O1.3 %Zr, with cylindrical rods of 12 mm in diameter. Esmailian et al. [21] studied RRA for AA7055 and got the maximum strength at 40 minutes retrogression time, 200°C retrogression temperature. The curve shape, illustrated in Figures 5 and 16 (retrogression 180°C and reaged at 120°C/24h) matches in shape in references [13], [14], and [21], As the specimens are retrogressed for an increasingly longer time, there is an initial decrease in hardness (Zone I). This produces a local minimum hardness at Retrogression Time "TR". After “TR” there is a slight increase in hardness (Zone II). There is a second decrease in hardness, Zone III (overaging the material). It was observed that the alloy AA7012 aged at 120°C/24h and retrogressed at 210°C and 240°C did not retrogress appropriately. The retrogression temperature in previous studies showed a variation of 200°C to 240°C, this is a function of the chemical composition of the alloy, aging parameters (T6 temper), and dimensions of the specimens used in the experiment. Precipitates morphology analysis regarding Circularity and Roundness at different RRA times (15 seconds, 1 hour, and 2 hours) did not detect a significant variation, a range of 0.02 µm and 0.06 µm was observed respectively. The Feret Diameter showed a range of 0.19 µm. Later analysis of the Feret Diameter at RRA 180°C / 3h - 210°C / 24h was done and the mean value detected was 1,20 µm. This suggests that between Circularity, Roundness, and Feret Diameter, the last one could be a morphology parameter to evaluate the precipitate morphology after RRA heat treatment for AA7012. Beyond the automotive industry, there is a large potential field for applications of aluminum alloy AA7012 RRA, it includes the Weapon industry as tail missile component and Medical application as PTA (Progressive Tibial Alignment) - external fixation system. For the RRA180 sample, the electrical conductivity reaches a maximum value of 46% IACS at TR of 60 minutes, which also corresponds to the maximum hardness obtained in this condition. For RRA210 and RRA240 there is an increase in electrical conductivity up to a TR of 15 minutes, but without reaching the maximum value found for RRA180. The precipitates of Al-Mg-Cu-Zn and Al-Mg-Si-Cu-Zn were detected. 5. Conclusion Of the three RRA cycles studied, only retrogression at 180°C showed the RRA curve by the bibliographies consulted, see Figure 2 (theoretical curve) and Figure 4, (result of the study). The process parameters for the retrogression of the AA7012 alloy using a cylindrical specimen with a diameter of 15 mm and a height of 30 mm are: i) Solution: 465°C for 2 hours. ii) Aging: 120°C for 24 hours. iii) Retrogression: 180°C for 1 hour. iv) Reaging: 120°C for 24 hours. The electrical conductivity value showed a peak value for the condition of RRA180 for 1 hour; this peak was also observed in the microhardness evaluation. The samples treated by RRA have higher electrical conductivity than the samples in their original condition, i.e. solubilized and aged (T6 temper). The maximum precipetate quantity correspond to was detected corresponde to the maximum hardness (RRA180). Abbreviations AA Aluminum Alloy Al Aluminum ALCAN Aluminum Company of Canada ALCOA Aluminum Company of America AR Aspect Ratio IACS International Annealed Copper Standard C Circularity Cu Cooper Δ Delta, Greek letter. To express variation G-P Guinier and Preston, Zone H Hour HV Hardness, Vickers LAR-NCR Institute for Aerospace Research, National Research Council of Canada Mg Magnesium min minute RRA Retrogression and ReagingCracking SEM Scanning Electron Microscopy SOL Solidity T6 Temper T6 – Solution and Aged to maximum mechanical properties (hardness). TR Time, Retrogression UNS Unified Number System Zn Zinc Declarations Availability of data and materials: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request. Competing interests: The authors declare that they have no competing interests. Funding: This research received external funding from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Brazil – Finance Code 001. Authors’ contributions: The author’s read and corrected the manuscript. The authors read ans approved the final manuscript.. Methodology, André Carvalho, Rogerio Hein and Luiz Rosa, Validation, Marcos Ribeiro; Investigation, Luiz Rosa,Resources, André Carvalho and Luiz Hein; Data Curation, Luiz Rosa; Writing—original draft preparation, Luiz Rosa; Writing—review and editing, Luiz Rosa; Visualization, Luiz Rosa; Supervision, Marcos Ribeiro; project administration, Luiz Rosa; Funding acquisition, Marcos Ribeiro. 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Materials Science and Engineering A 379 (2004), pp. 321–326. doi:10.1016/j.msea.2004.02.052 ImageJ – Viewed on April/22 nd /2024.available at: image.net/ij/docs/index.html Supplementary Files AnnexI.docx Cite Share Download PDF Status: Published Journal Publication published 24 Apr, 2025 Read the published version in Journal of Materials Science: Materials in Engineering → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5389427","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":375504220,"identity":"4e9dfe0d-55f3-4e44-89b0-7b6ab896ec27","order_by":0,"name":"Luiz Rosa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAw0lEQVRIiWNgGAWjYBACPhiDH0onENTCBmNINpCsxeAA0VrYDz9grqiokze+kXvw4c8dDHnmDYS08KQZMJ45c9hw2428ZGPeMwzFMgcIOizBgLGx7QDjths5ZtKMbQyJMwg6jP/5B6CWOvvNM3LMf/4kSotEDsgW5sQNEjlmDLzEaXlTcLDhzOHkGWfeGEvznpEoliCkhZ8/fePDhoo62/72HMOPP3fY5BHUAgIH4CzGBqI0IAPGBlJ1jIJRMApGwUgAALjuO8pgx19uAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0009-0009-6733-9205","institution":"UNESP FEG: Universidade Estadual Paulista Julio de Mesquita Filho Faculdade de Engenharia e Ciencias","correspondingAuthor":true,"prefix":"","firstName":"Luiz","middleName":"","lastName":"Rosa","suffix":""},{"id":375504221,"identity":"66f444b4-6859-456d-9428-fbf14a9e4c0d","order_by":1,"name":"André Luís Moreira de Carvalho","email":"","orcid":"","institution":"Universidade Estadual de Ponta Grossa","correspondingAuthor":false,"prefix":"","firstName":"André","middleName":"Luís Moreira","lastName":"de Carvalho","suffix":""},{"id":375504222,"identity":"0c112e2d-229f-463f-8587-6ba0b4e77c68","order_by":2,"name":"Luis Rogerio de Oliveira Hein","email":"","orcid":"","institution":"UNESP FEG: Universidade Estadual Paulista Julio de Mesquita Filho Faculdade de Engenharia e Ciencias","correspondingAuthor":false,"prefix":"","firstName":"Luis","middleName":"Rogerio de Oliveira","lastName":"Hein","suffix":""},{"id":375504223,"identity":"bfaab4ff-a222-41a0-ab6f-7f0ef422e98c","order_by":3,"name":"Marcos Valério Ribeiro","email":"","orcid":"","institution":"UNESP FEG: Universidade Estadual Paulista Julio de Mesquita Filho Faculdade de Engenharia e Ciencias","correspondingAuthor":false,"prefix":"","firstName":"Marcos","middleName":"Valério","lastName":"Ribeiro","suffix":""}],"badges":[],"createdAt":"2024-11-04 15:45:55","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5389427/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5389427/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40712-025-00269-w","type":"published","date":"2025-04-24T15:58:27+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":69927399,"identity":"48459ed4-84fe-4303-acd0-b2d84258a967","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":37679,"visible":true,"origin":"","legend":"\u003cp\u003eRRA schematic diagram.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/0fe42df71295e049eb820239.png"},{"id":69927382,"identity":"5d1ad8b5-fa34-4ae4-88d2-0d13d44a0b1b","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":51749,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of RRA. TR is retrogression time\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/ae85c5b95a1483fe84744770.png"},{"id":69928260,"identity":"9080c6e5-e113-4be1-98f7-4fab8d5e4034","added_by":"auto","created_at":"2024-11-26 16:58:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":460930,"visible":true,"origin":"","legend":"\u003cp\u003eSalt Bath Furnace used for Retrogression Heat Treatment.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/829ce7b78245346776d51bb2.png"},{"id":69927564,"identity":"4d60559a-84d4-49d0-8744-41cd04cf6452","added_by":"auto","created_at":"2024-11-26 16:50:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":310627,"visible":true,"origin":"","legend":"\u003cp\u003eConductivity meter and Probe.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/dc6a7dadbfc77f17c41b0c14.png"},{"id":69927386,"identity":"706313f9-3d43-4483-8039-2b351d23118b","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":61990,"visible":true,"origin":"","legend":"\u003cp\u003eRRA Curve, 180°C and reaged at 120°C / 24h\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/0372513db196dd2ae4db25cf.png"},{"id":69927396,"identity":"9b692eea-56b4-48e9-836d-a3335c3dada3","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":49737,"visible":true,"origin":"","legend":"\u003cp\u003eRRA Curve, 210°C and reaged at 120°C / 24h\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/a28a815b5c51ab9864400511.png"},{"id":69927388,"identity":"b28edd75-27b1-4058-ac2d-c991d57eed5e","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":41346,"visible":true,"origin":"","legend":"\u003cp\u003eRRA Curve 240°C and reaged at 120°C / 24h\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/93d6895a444345690a66150f.png"},{"id":69927401,"identity":"ff1c56bd-d159-4ce8-85e4-85f3531c3d40","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":145770,"visible":true,"origin":"","legend":"\u003cp\u003eRetrogressed at 180°C/15 seconds and Reaged at 120°C/ 24h.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/090b44fc1ad680b96f0a4f5f.png"},{"id":69927394,"identity":"f10136a9-7706-4df9-8db0-e8f761b3d694","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":54306,"visible":true,"origin":"","legend":"\u003cp\u003eRetrogressed at 180°C/1h and Reaged at 120°C/ 24h.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/e4f9bbd0fc795ba2b1b3fb65.png"},{"id":69927566,"identity":"fcd7e71c-ee83-4c3f-a57a-aee7add75511","added_by":"auto","created_at":"2024-11-26 16:50:26","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":61943,"visible":true,"origin":"","legend":"\u003cp\u003eRetrogressed at 180°C/2h and Reaged at 120°C/ 24h.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/4a224816a1761573870b8cfc.png"},{"id":69927395,"identity":"f15c398b-3d24-4736-8683-806945e2eabd","added_by":"auto","created_at":"2024-11-26 16:42:26","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":17713,"visible":true,"origin":"","legend":"\u003cp\u003eNumber of precipitates versus retrogression time. 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Retrogression at 180°C/1h and reaged at 120°C/24h. Precipitate: Mg, Cu e Zn.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-5389427/v1/b451623b1ca599225b3d0b6b.png"},{"id":69927569,"identity":"aca5216c-cc1a-445e-ab4d-9bdfe912a339","added_by":"auto","created_at":"2024-11-26 16:50:26","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":146018,"visible":true,"origin":"","legend":"\u003cp\u003eSEM. Retrogression at 180°C/1h and reaged at 120°C/24h. 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Aluminum and its alloys meet the requirement of low value for money when the ratio of mechanical properties to component mass is considered. The extraction and processing of aluminum have an environmental impact, but this impact can be reduced by recycling [1].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHigh-strength aluminum alloys are of interest to the automotive industry because of their potential to reduce the mass of components. Generally, high-strength alloys have high Yield and Strength limits, 500 and 570 MPa, respectively, and a low density compared to steel, 2.8 g/cm\u003csup\u003e3\u003c/sup\u003e versus 7.7 g/cm\u003csup\u003e3\u0026nbsp;\u003c/sup\u003e[2]. \u0026nbsp;The the good corrosion resistance, excellent workability, high ratio of mechanical strength to density, and appropriate electrical and heat conductivity, classify aluminum alloys for the manufacture of industrial components and automotive components such as pistons, steering gears, engine blocks, wheels [3], and also pumpers. These components potentially can be made with AA7012 by applying the RRA heat treatment. All of these factors make aluminum alloys attractive to the automotive industry.\u003c/p\u003e\n\u003cp\u003eThe Retrogression and Reaging (RRA) heat treatment was introduced by Cina and his colleagues, in Israel, in the early 1970s, to improve the mechanical strength and stress corrosion cracking of AA 7075-T6, using temperatures between 200\u0026deg;C and 280\u0026deg;C and time from 1 to 30 seconds with material 2.8 mm thick [4] and [5]. Since 1980, LAR-NCR (Institute for Aerospace Research, National Research Council of Canada) has been working on the development of retrogression and reaging heat treatment technology with material up to 6.35mm thick [5].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe RRA is a two-stage heat treatment that improves the mechanical properties and stress corrosion resistance (SCC) of 7xxx series aluminum alloys. The alloy to be treated must be at T6 temper, the first stage is retrogression made to a temperature between the aging temperature and the solubilization, and the second stage is the artificial reaging - identical to the parameters to obtain T6 temper, generally 120\u0026deg;C for 24 hours. The schematic diagram used in this study is shown in Figure 1, including solubilization, aging, retrogression, and reaging.\u003c/p\u003e\n\u003cp\u003eThis study aims to determine the RRA curve for AA7012 (Al-Zn-Mg-Cu-Zr), as well as the respective process parameters. This is of interest to the automotive industry. The use of lighter materials with adequate mechanical strength has become a constant request for vehicle manufacturers. Gears, axles, and bumpers are potential components to be manufactured with AA7012 applying the RRA heat treatment.\u003c/p\u003e\n\u003cp\u003eThe AA7012 alloy is characterized by a Zn/Mg (mass) ratio of approximately 3, a copper content of around 1% by mass, and the presence of zirconium and manganese replacing chromium as dispersoid-forming elements. The chemical composition of the AA7012 alloy is characterized by the following parameters:\u003c/p\u003e\n\u003cp\u003ei) The iron and silicon contents are reduced to the maximum permitted values, % by mass, of 0.25% and 0.15% respectively. The concentrations of \u0026alpha;-AlFeSi, Al\u003csub\u003e7\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eFe, Mg\u003csub\u003e2\u003c/sub\u003eSi, and (Fe,Cu,Mn)Al\u003csub\u003e6\u003c/sub\u003e are reduced, increasing the toughness value. Iron and silicon drag down magnesium and copper, reducing their contribution to age hardening. The chemical composition of the AA7012 alloy is shown in Table 1 [7] and [8].\u003c/p\u003e\n\u003cp\u003eii) Zirconium, in a controlled percentage, replaces chromium to control recrystallization, forming the Al\u003csub\u003e3\u003c/sub\u003eZr dispersoid. The removal of chromium eliminates the formation of Al\u003csub\u003e18\u003c/sub\u003eCr\u003csub\u003e6\u003c/sub\u003eMg\u003csub\u003e2\u003c/sub\u003e, which removes magnesium from the alloy, thus reducing its hardening effect on aging.\u003c/p\u003e\n\u003cp\u003eiii) The percentage by mass of zinc is not less than 5.8% and the minimum percentage of copper and magnesium is 0.8% and 1.8% (by mass) respectively.\u003c/p\u003e\n\u003cp\u003eiv) Presence of titanium and manganese in controlled percentages.\u003c/p\u003e\n\u003cp\u003ev) The AA7012 is less sensitive to quench rate when compared with AA7075.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe chemical composition of the \u0026nbsp;AA7012 aluminum alloy is shown in Table 1 [6].\u003c/p\u003e\n\u003cp\u003eTable 1. Chemical \u0026nbsp;Composition AA7012 \u0026nbsp;(mass %) \u0026ndash; [6]\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"567\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 16.5785%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAA7012\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.17108%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eZn\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMg\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCu\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.4056%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eTi\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSi\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 7.93651%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFe\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.7584%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eMn\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 7.93651%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCr\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.17108%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eZr\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 16.5785%;\"\u003e\n \u003cp\u003eSpecification\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.17108%;\"\u003e\n \u003cp\u003e5.8 \u0026ndash;6.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e1.8 \u0026ndash; 2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e0.8 \u0026ndash; 1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.4056%;\"\u003e\n \u003cp\u003e0.02 \u0026ndash; 0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.34744%;\"\u003e\n \u003cp\u003e0.15 max\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 7.93651%;\"\u003e\n \u003cp\u003e0.25 max\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.7584%;\"\u003e\n \u003cp\u003e0.08 \u0026ndash; 0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 7.93651%;\"\u003e\n \u003cp\u003e0.04 max\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.17108%;\"\u003e\n \u003cp\u003e0.10 \u0026ndash; 0.18\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDue to the high solubility of zinc (82.8% - mass) and magnesium (14.9% - mass) in solid aluminum [7], the mechanical properties of 7xxx series alloys can be significantly increased through solubilization heat treatment and artificial aging. The increase in hardness and mechanical properties is due to the precipitates formed in the microstructure and obstructing the movement of dislocations [8]. The Liquidus and Solidus temperatures of AA7012 are 636\u0026deg;C and 475\u0026deg;C respectively [9]. The precipitation hardening induced by artificial aging of the 7xxx series aluminum alloys and accepted for the AA7012 alloy is described in Equation 1 [10] and [11]:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" style=\"width: 530px; height: 23.0078px;\" width=\"530\" height=\"23.0078\"\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u003c/p\u003e\n\u003cp\u003ewhere:\u003c/p\u003e\n\u003cp\u003ea) Al\u003csub\u003e\u0026alpha;sss\u003c/sub\u003e is the supersaturated solid solution of aluminum that is retained after \u0026nbsp;cooling, usually in water.\u003c/p\u003e\n\u003cp\u003eb) G-P zones are the Guinier and Preston I and II zones.\u003c/p\u003e\n\u003cp\u003ec) Precipitate \u0026eta;\u0026apos;: metastable phase, MgZn\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003ed) Precipitate \u0026eta;: equilibrium phase, MgZn\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003eDuring aging there is fine precipitation of the G-P Zones inside the grains, and as a consequence, there is an increase in the hardness of the alloy [12] and [13]. Buha and his colleagues [13] indicate the formation of two types of G-P Zones:\u003c/p\u003e\n\u003cp\u003e1) G-P I zones, exhibit a spherical morphology, composed of ordered and coherent layers of Zn and Mg/Al atoms on {111}\u003csub\u003eAl\u003c/sub\u003e.\u003c/p\u003e\n\u003cp\u003e2) G-P II zones, exhibit a platelet morphology composed of layers of zinc in {111}\u003csub\u003eAl\u003c/sub\u003e. G-P II Zones form after cooling from 450\u0026deg;C and when aged above 70\u0026deg;C.\u003c/p\u003e\n\u003cp\u003eOn T6 temper, the aluminum alloy 7012 has a minimum Tensile \u003csub\u003e(0.2%)\u003c/sub\u003e Strength and minimum Yield Strength of 560 MPa and 520 MPa respectively, and a minimum elongation\u003csub\u003e(50 mm)\u003c/sub\u003e of 6% [9]. The typical curve resulting from RRA heat treatment (time versus hardness is shown in Figure 2 \u0026nbsp;[14], [15], [16] and [17]. During retrogression, the hardness initially decreases to a minimum value until the retrogression time (TR) - Zone I, this is caused by the dissolution of the G-P and/or \u0026eta;\u0026apos; Zones formed during aging. After the TR the hardness increases again to a local maximum value - Zone II, this increase in hardness is associated with the growth of the \u0026eta;\u0026apos; phase and precipitation of the \u0026eta; phase [18]. After reaching the maximum local hardness there is a reduction in hardness values due to the over-aging of the alloy. The slight recovery of hardness after TR is due to the precipitation and growth of \u0026eta; precipitates [5]. When the time of the retrogression stage is short enough to allow only the dissolution of precipitates, the subsequent reaging at 120\u0026deg;C for 24 hours will bring the material back to maximum hardness [4].\u003c/p\u003e\n\u003cp\u003eThe recommended retrogression time is identified by TR on Figure 2. If the alloy is retrogressed for a longer time than TR, the original hardness of the T6 hardening may not be recovered by subsequent reannealing because the solute elements agglomerate, preventing the formation of \u0026eta;\u0026apos; and \u0026eta;\u0026apos; precipitates. Feng et al. [18] indicate the occurrence of three main reactions during retrogression: 1) partial dissolution of the G-P Zones and the \u0026eta;\u0026apos; phase, which are responsible for the reduction in hardness observed in Zone I; 2) formation of growth of the \u0026eta;\u0026apos; phase, which is responsible for the increase in local hardness (Zone II), and 3) agglomeration of precipitates, which causes the reduction in hardness (Zone III).\u003c/p\u003e\n\u003cp\u003eNing et al. [19] studied the 7xxx series aluminum alloys, 6.28Zn-2.19Mg-1.6Cu-0.15Cr, solubilized at 470\u0026deg;C/1 hour; aged at 120\u0026deg;C/24h (T6 hardening) and retrograded at 200\u0026deg;C and reaged according to the parameters used in the T6 hardening, the retrogression time (TR) obtained was 6 minutes; for the alloy 9. 99Zn-2.5Mg-1.72Cu-0.13Zr alloy, solubilized at 450\u0026deg;C/2h plus 470\u0026deg;C/1h and retempered at 200\u0026deg;C and reaged according to the parameters used in the T6 tempering, the retrogression time (TR) obtained was 7 minutes. Different regression times were used for both alloys, ranging from 2 to 45 minutes. The shape of the RRA curve (HV hardness versus time in minutes) corresponds to that shown in Figure 2; there is no mention of the dimensions of the specimens used to determine the RRA curve. The aluminum alloy 9.99Zn-2.5%Mg-1.72%Cu-0.13 %Zr was also studied by Feng et al. [18], the study was carried out on samples aged at 100\u0026deg;C/24h (T6), retempered at 200\u0026deg;C/7 minutes and reaged. The samples were cylindrical, 12 mm in diameter. Park and Ardel [20] studied the AA7075 T651 alloy; the samples used to draw up the RRA curve were 0.25 mm thick. The retrogression was carried out in a salt bath at 240\u0026deg;C for various times up to 60 seconds and re-aged at 120\u0026deg;C/48h in an oil bath. The observed retorting time was 24 seconds. Ural [16] \u0026nbsp;and Esmailian et al. [21] also studied the AA7075 alloy, in the first study the maximum hardness was obtained with a temperature and regression time of 200\u0026deg;C/40 minutes, after re-aging for 120\u0026deg;C/24h, in the second study, using a silicon bath, the conditions established for the RRA were 200\u0026deg;C / 45 - 60 minutes and re-aging at 120\u0026deg;C/24h, in the second study the samples were 25.4 mm thick. Crawford et al. [17] mention that using temperatures of around 180\u0026deg;C - 195\u0026deg;C prolongs the retrogression stage, making it easier to control the process.\u003c/p\u003e\n\u003cp\u003eExperiments by the Institute of Aerospace Research (IAR) from Canada working with the aluminum alloy AA7075-T6511 controlled the RRA process by electrical conductivity. The better condition in terms of electrical conductivity was 38,5% IACS (International Annealed Cooper Standard [5]. Oliveira et al. [studied AA7050, 2.5 mm thick, for a retrogression time of 40 minutes and got values of 36 \u0026ndash; 39 % IACS, the maximum value was for an aging time of 1000 minutes.\u0026nbsp;\u003c/p\u003e"},{"header":"2.\tMaterials and Methods","content":"\u003cp\u003eThe material used in this study was supplied by ALCOA - Brazil as an extruded AA7012 aluminum bar (15 mm diameter and 700 mm long). The AA7012 alloy was produced by the direct extrusion process, homogenized, and supplied as manufactured. The nominal composition is shown in Table 2.\u003c/p\u003e\n\u003cp\u003eTable 2. Chemical \u0026nbsp;Composition AA7012 \u0026nbsp;(mass %)\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"567\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 16.0777%;\"\u003e\n \u003cp\u003eAA7012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003eZn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.0707%;\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.12721%;\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.424%;\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.54064%;\"\u003e\n \u003cp\u003eCr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.0106%;\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 16.0777%;\"\u003e\n \u003cp\u003eSample \u0026nbsp;RRA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003e5.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003e1.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.0707%;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.18728%;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 8.12721%;\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 10.424%;\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.54064%;\"\u003e\n \u003cp\u003e0,002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 9.0106%;\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eNote:\u003c/strong\u003e The Zn/Mg ratio for the sample under study is 3.05.\u003c/p\u003e\n\u003cp\u003eThe solubilization heat treatment was carried out on 150 mm bars. The bars were cut with a hand saw and solubilized at 465\u0026deg;C for 2 hours in an EDG 7000/FDG 3P-S furnace, and cooled in water at 25\u0026deg;C with moderate stirring. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe aging process was carried out in an EDG 7000/FDG 3P-S furnace, \u0026Oslash; 15mm and 30 mm long specimens were used for artificial aging, which was carried out at 120\u0026deg;C for 24 hours, cooled in still air.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThree different temperatures of 180\u0026deg;C, 210\u0026deg;C and 240\u0026deg;C were used for the retrogression, with step times of 5s, 10s, 15s, 20s, 30s, 1min, 5min, 15min, 30min, 60min, 120min, 180min and 240 min. \u0026nbsp; Retrogression was carried out in a salt bath using AS 140 salt by HEF\u0026trade; DURFERRIT, Figure 3.\u003c/p\u003e\n\u003cp\u003eAfter regression, the samples were washed in running water with neutral soap. Re-aging was carried out in an EDG 7000/FDG 3P-S oven at 120\u0026deg;C for 24 hours, cooled in still air.\u003c/p\u003e\n\u003cp\u003eThe metallographic preparation was carried out in four stages: 1) Cutting: TECHCUT 4 automatic saw - ALLIED - HIGH TECH PRODUCTS, INC. with a diamond disk at 200rpm. 2) Embedding: AROTEC hydraulic press and bakelite. 3) Sanding: METPREP 3, PH - 3 automatic polishing machine, using water as a lubricant and sandpaper of 320, 400, 600, 800, 1200, 2000 and 2400 (mesh). 4) Polishing: VIBRATORY POLISHER, PACE TECHNOLOGIES, GIGA - 0900, silica 0.02\u0026micro;m (50%) for 24 hours.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Microstructural analysis was carried out considering the number of preciptates and their morphology and size. The following parameters were used for morphological analysis: Circularity (C) , Solidity (SOL) and Aspect Ratio (AR), for dimensional analysis the Feret Diameter was used. This analysis was carried out using a Zeiss AxioImager Z2m optical microscope. The analysis macro was created using ImageJ software (Image Processing and Analysis in Java [20]. A total of 121 regions were analyzed. ImageJ Routine is shown on Annex I. Scanning Electron Microscopy (SEM) analysis was carried out using the Zeiss EVO LS 15 SEM electron microscope and EDS (Energy Dispersive Spectroscopy) Oxford Instruments Xplore 30.\u003c/p\u003e\n\u003cp\u003eCircularity is defined as C = 4.\u0026pi;. Area / Perimeter\u003csup\u003e2\u003c/sup\u003e, it is a dimensionless number defined in the interval (0,1], Solidity (SOL) is defined as the ratio between Area / Convex Area, it is a dimensionless number defined in the interval (0,1]. Aspect Ratio (AR) is defined as the ratio between width (L) and height (h). The Feret diameter is defined as the maximum distance between two parallel, tangent points on opposite sides of the image of a randomly oriented particle. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe Vickers hardness measurement (HV) was evaluated at half the radius of the samples (diameter 15 mm) in a Wilson Instruments Model 401 MDV microhardness tester using a 500-gram rod with a penetration time of 15 seconds. The hardness assessment was carried out at room temperature.\u003c/p\u003e\n\u003cp\u003eTo measure electrical conductivity, the samples were stabilized at 20\u0026deg;C for 24 hours. A portable SIGNASCOPE\u0026reg; Fisher SERIAL 4502 conductivity meter and a 14mm diameter probe was used. The results were given in percentage according to the International Annealed Copper Standard (IACS).\u003c/p\u003e"},{"header":"3.\tResults","content":"\u003cp\u003eThe RRA curves obtained for 180\u0026deg;C, 210\u0026deg;C and 240\u0026deg;C retrogression, both re-aged at 120\u0026deg;C / 24h are illustrated in figures 5, 6 and 7 respectively. The hardness in the T6 condition was 184HV. Only the material retrogressed at 180\u0026deg;C/1h and reaged at 120\u0026deg;C/24h have a significante increse on hardnesss, i.e., from 160 HV to 220 HV, an increase of 37.5% and comparing with T6 original hardness (184 HV) and incresse of 19.5% was observed.\u003c/p\u003e\n\u003cp\u003eThe morphology of the precipitates were analyzed for the conditions that showed retrogressed at 180\u0026deg;C: i) sample reaged for 15 seconds (within Zone I), 1 hour (within Zone II - TR) and 2 hours (within Zone 3). The morphology of the precipitates is shown in Figures 8, 9 and 10.\u003c/p\u003e\n\u003cp\u003eThe results of the morphological and dimensional analysis are shown in Tables 3, 4 and 5.\u003c/p\u003e\n\u003cp\u003eTable 3. \u0026nbsp;Retrogression:180\u0026deg;C/15seconds \u0026ndash; Reaging:210\u0026deg;C/ 24h\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCircularity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeret Diameter\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;(\u0026micro;m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAspect Ratio (AR)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolidity (Sol)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eAverage\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eStd. Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e7.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e3.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003ePrecipitate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 453px;\"\u003e\n \u003cp\u003e72918\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTable 4 . \u0026nbsp; Retrogression:180\u0026deg;C/1h \u0026ndash; Reaging:210\u0026deg;C/24h\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCircularity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeret Diameter\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;(\u0026micro;m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAspect Ratio (AR)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolidity (Sol)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eAverage\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.88\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eStd. Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e11.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e3.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003ePrecipitate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 453px;\"\u003e\n \u003cp\u003e103313\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTable 5. \u0026nbsp; Retrogression:180\u0026deg;C/ 2h \u0026ndash; Reaging:210\u0026deg;C/ 24h\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCircularity\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eFeret Diameter\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;(\u0026micro;m)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAspect Ratio (AR)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eSolidity (Sol)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eAverage\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eStd. Deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003eMax\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e7.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e3.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 113px;\"\u003e\n \u003cp\u003ePrecipitate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"4\" valign=\"top\" style=\"width: 453px;\"\u003e\n \u003cp\u003e95073\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe quantity of precipitates are indicated in Figure 11 for Retrogression at 180\u0026deg;C and reaged at 120\u0026deg;C/24h.\u003c/p\u003e\n\u003cp\u003eThe results of measured electrical conductivity, are indicated in Figure 12 to Retrogression at 180\u0026deg;C, 210\u0026deg;C e 240\u0026deg;C, reaging at 120\u0026deg;C/24h.\u003c/p\u003e\n\u003cp\u003eThe SEM of the precipitates were analyzed for the conditions that showed retrogressed at 180\u0026deg;C: i) sample reaged for 15 seconds (within Zone I), 1 hour (within Zone II - TR) and 2 hours (within Zone 3). The morphology of the precipitates is shown in Figures 13, 14 and 15.\u003c/p\u003e"},{"header":"4.\tDiscussion","content":"\u003cp\u003eThere is a large discrepancy in retrogression treatment time (TR) between the authors consulted. The main cause is the variation in the thickness of the specimens used in the studies, i.e. from 0.25 mm to 25.4 mm and the aluminum alloy used on the study. The retrogression temperatures reported were always higher than the aging temperature and lower than the solubilization temperature.\u003c/p\u003e\n\u003cp\u003eNing et al. [19] studied a 7xxx series (6.28Zn-2.19Mg-1.6Cu-0.15Cr) that got retrogression process parameters of 200\u0026deg;C/7 minutes, no reference to the specimen thickness was reported in their study. Park and Ardel [20] for the AA7075 got a retrogression parameter of 240\u0026deg;C/25 seconds for thin samples cut in strips of 0.25mm in thickness. Feng et al. [18] got retrogression parameters of 200\u0026deg;C/7minutes studying the alloy Al-9.99Zn-1.72%Cu-2.5%Mg-O1.3 %Zr, with cylindrical rods of 12 mm in diameter. \u0026nbsp;Esmailian et al. [21] studied RRA for \u0026nbsp;AA7055 and got the maximum strength at 40 minutes retrogression time, 200\u0026deg;C retrogression temperature.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe curve shape, illustrated in Figures 5 and 16 (retrogression 180\u0026deg;C and reaged at 120\u0026deg;C/24h) matches in shape in references [13], [14], and [21], As the specimens are retrogressed for an increasingly longer time, there is an initial decrease in hardness (Zone I). This produces a local minimum hardness at Retrogression Time \u0026quot;TR\u0026quot;. After \u0026ldquo;TR\u0026rdquo; there is a slight increase in hardness (Zone II). There is a second decrease in hardness, Zone III (overaging the material). It was observed that the alloy AA7012 aged at 120\u0026deg;C/24h and retrogressed at 210\u0026deg;C and 240\u0026deg;C did not retrogress appropriately.\u003c/p\u003e\n\u003cp\u003eThe retrogression temperature in previous studies showed a variation of 200\u0026deg;C to 240\u0026deg;C, this is a function of the chemical composition of the alloy, aging parameters (T6 temper), \u0026nbsp;and dimensions of the specimens used in the experiment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePrecipitates morphology analysis regarding Circularity and Roundness at different RRA times (15 seconds, 1 hour, and 2 hours) did not detect a significant variation, a range of 0.02 \u0026micro;m and 0.06 \u0026micro;m was observed respectively. The Feret Diameter showed a range of 0.19 \u0026micro;m. Later analysis of the Feret Diameter at RRA 180\u0026deg;C / 3h - 210\u0026deg;C / 24h was done and the mean value detected was 1,20 \u0026micro;m. This suggests that between Circularity, Roundness, and Feret Diameter, the last one could be a morphology parameter to evaluate the precipitate morphology after RRA heat treatment for AA7012.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBeyond the automotive industry, there is a large potential field for applications of aluminum alloy AA7012 RRA, it includes the Weapon industry as tail missile component and Medical application as PTA (Progressive Tibial Alignment) - external fixation system.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the RRA180 sample, the electrical conductivity reaches a maximum value of 46% IACS at TR of 60 minutes, which also corresponds to the maximum hardness obtained in this condition. For RRA210 and RRA240 there is an increase in electrical conductivity up to a TR of 15 minutes, but without reaching the maximum value found for RRA180. The precipitates of Al-Mg-Cu-Zn and \u0026nbsp;Al-Mg-Si-Cu-Zn were detected.\u003c/p\u003e"},{"header":"5.\tConclusion","content":"\u003cp\u003eOf the three RRA cycles studied, only retrogression at 180\u0026deg;C showed the RRA curve by the bibliographies consulted, see Figure 2 (theoretical curve) and Figure 4, (result of the study). The process parameters for the retrogression of the AA7012 alloy using a cylindrical specimen with a diameter of 15 mm and a height of 30 mm are:\u003c/p\u003e\n\u003cp\u003ei) Solution: 465\u0026deg;C for 2 hours.\u003c/p\u003e\n\u003cp\u003eii) Aging: 120\u0026deg;C for 24 hours.\u003c/p\u003e\n\u003cp\u003eiii) Retrogression: 180\u0026deg;C for 1 hour.\u003c/p\u003e\n\u003cp\u003eiv) Reaging: 120\u0026deg;C for 24 hours.\u003c/p\u003e\n\u003cp\u003eThe electrical conductivity value showed a peak value for the condition of RRA180 for 1 hour; this peak was also observed in the microhardness evaluation. The samples treated by RRA have higher electrical conductivity than the samples in their original condition, i.e. solubilized and aged (T6 temper).\u003c/p\u003e\n\u003cp\u003eThe maximum precipetate quantity correspond to was detected corresponde to the maximum hardness (RRA180).\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Aluminum Alloy\u003c/p\u003e\n\u003cp\u003eAl\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Aluminum\u003c/p\u003e\n\u003cp\u003eALCAN\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Aluminum Company of Canada\u003c/p\u003e\n\u003cp\u003eALCOA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Aluminum Company of America\u003c/p\u003e\n\u003cp\u003eAR\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Aspect Ratio\u003c/p\u003e\n\u003cp\u003eIACS \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;International Annealed Copper Standard\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eC\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Circularity\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCu\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Cooper\u003c/p\u003e\n\u003cp\u003e\u0026Delta;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Delta, Greek letter. To express variation\u003c/p\u003e\n\u003cp\u003eG-P \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Guinier and Preston, Zone \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eH\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Hour\u003c/p\u003e\n\u003cp\u003eHV\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Hardness, Vickers\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLAR-NCR \u0026nbsp; \u0026nbsp; Institute for Aerospace Research, National Research Council of \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Canada\u003c/p\u003e\n\u003cp\u003eMg\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Magnesium\u003c/p\u003e\n\u003cp\u003emin\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;minute\u003c/p\u003e\n\u003cp\u003eRRA\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Retrogression and ReagingCracking\u003c/p\u003e\n\u003cp\u003eSEM\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Scanning Electron Microscopy\u003c/p\u003e\n\u003cp\u003eSOL\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Solidity\u003c/p\u003e\n\u003cp\u003eT6\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Temper T6 \u0026ndash; Solution and Aged to maximum mechanical properties (hardness).\u003c/p\u003e\n\u003cp\u003eTR\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Time, Retrogression\u003c/p\u003e\n\u003cp\u003eUNS\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Unified Number System\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eZn \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Zinc\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and materials:\u0026nbsp;\u003c/strong\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research received external funding from Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior (CAPES) \u0026ndash; Brazil \u0026ndash; Finance Code 001.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions:\u0026nbsp;\u003c/strong\u003eThe author\u0026rsquo;s read and corrected the manuscript. The authors read ans approved the final manuscript..\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMethodology, Andr\u0026eacute; Carvalho, Rogerio Hein and Luiz Rosa, Validation, Marcos Ribeiro; \u0026nbsp;Investigation, Luiz Rosa,Resources, Andr\u0026eacute; Carvalho and Luiz Hein;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData Curation, Luiz Rosa; Writing\u0026mdash;original draft preparation, Luiz Rosa; Writing\u0026mdash;review and editing, Luiz Rosa; Visualization, Luiz Rosa; Supervision, Marcos Ribeiro; project administration, Luiz Rosa; Funding acquisition, Marcos Ribeiro.\u003c/p\u003e\n\u003cp\u003eAll authors have read and agreed to the published version of the manuscript.\u0026nbsp;\u003c/p\u003e "},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWilliams, J. C and Starke Jr, E. A. Progress in structural materials for aerospace systems. 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A research on the effect of retrogression and re-aging heat treatment on hot tensile Properties of AA7075 aluminum alloys. Journal of Manufacturing Science and Engineering. January 2022, Vol. 144 / 011055-1https://doi.org/10.1115/1.4051436\u003c/li\u003e\n\u003cli\u003eHydro \u0026ndash; Ligas e T\u0026ecirc;mperas de Extrus\u0026atilde;o. Perf\u0026iacute;s dExtrudados de Alum\u0026iacute;nio. Cat\u0026aacute;logo de Ligas e T\u0026ecirc;mperas de Extrus\u0026atilde;o \u0026ndash; Edi\u0026ccedil;\u0026atilde;o 01, pp. 46 \u0026ndash; 47.https://www.hydro.com/globalassets/08-about-hydro/hydro-orldwide/brasil/extrudados/materiais-tecnicos/catalogo-ligas-e-temperas_a4_220322.pdf\u003c/li\u003e\n\u003cli\u003eHou, L. G.; Yu, H.; Wang, Y. W.; You, L.; He, Z. B.; Wu, C. M., Eskin, D. G.; Katgerman, L.; Zhuang, L. Z.; and Zhang, J. S. Tailoring precipitation/properties and related mechanisms for a high-strength aluminum alloy plate via low-temperature retrogression and re-aging processes. 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Metallurgical Transactions A, Volume 15A, August 1984, pp. 1531- 1543.https://link.springer.com/article/10.1007/BF02657792\u003c/li\u003e\n\u003cli\u003eM. Esmailian, M. Shakouri, A. Mottahedi, S.G. Shabestari, Effect of T6 and re-aging heat treatment on mechanical properties of 7055 aluminum alloy. World Academy of Science, Engineering and Technology International Journal of Materials and Metallurgical Engineering Vol: 9, No:11, 2015, pp. 1303 \u0026ndash; 1306. \u003cu\u003escholar.waset.org/1307-6892/10002916\u003c/u\u003e\u003c/li\u003e\n\u003cli\u003eOliveira Jr, A. F.; Barros, M. C.; Cardoso, K. R; and Travessa, D. N. The effect of RRA on the strength and SCC resistance on AA7050 and AA7150 aluminium alloys. Materials Science and Engineering A 379 (2004), pp. 321\u0026ndash;326. doi:10.1016/j.msea.2004.02.052\u003c/li\u003e\n\u003cli\u003eImageJ \u0026ndash; Viewed on April/22\u003csup\u003end\u003c/sup\u003e/2024.available at: image.net/ij/docs/index.html \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":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Aluminum Alloy, Retrogression, Reaging, AA7012 ","lastPublishedDoi":"10.21203/rs.3.rs-5389427/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5389427/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Retrogression and Reaging (RRA) is of interest to the automotive industry for manufacturing components of high-strength aluminum alloys. This study describes obtaining the Retrogression and Reaging curve for the aluminum alloy AA7012-T6 (Al-Zn-Mg-Cu) – UNS A97012. The RRA heat treatment consists of two stages: the first stage is retrogression, which was carried out on the samples in the T6 hardening condition for a time ranging from 5 seconds to 4 hours and at different temperatures: 180°C, 210°C, and 240°C. The second stage, re-aging, was conducted at 120°C for 24 hours (process parameters for obtaining the T6 temper). The RRA curve was obtained by measuring hardness Vickers (HV). The samples were also evaluated for electrical conductivity (%IACS - International Annealed Copper Standard ). The best response for the RRA curve was obtained with retrogression at 180°C/1h and re-aging at 120°C for 24 hours. The increase in hardness (HV) obtained with RRA 180°C/1h and reaged at 120°C/24h was 19%.","manuscriptTitle":"Retrogression and Reaging – Aluminum Alloy AA7012","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 16:42:21","doi":"10.21203/rs.3.rs-5389427/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"08b51e98-17ce-4024-b19d-0e01248bec85","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-04-28T16:04:30+00:00","versionOfRecord":{"articleIdentity":"rs-5389427","link":"https://doi.org/10.1186/s40712-025-00269-w","journal":{"identity":"journal-of-materials-science-materials-in-engineering","isVorOnly":true,"title":"Journal of Materials Science: Materials in Engineering"},"publishedOn":"2025-04-24 15:58:27","publishedOnDateReadable":"April 24th, 2025"},"versionCreatedAt":"2024-11-26 16:42:21","video":"","vorDoi":"10.1186/s40712-025-00269-w","vorDoiUrl":"https://doi.org/10.1186/s40712-025-00269-w","workflowStages":[]},"version":"v1","identity":"rs-5389427","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5389427","identity":"rs-5389427","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}