Vol. 26 No. 1 2024 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases.
OBRABOTKAMETALLOV Vol. 26 No. 1 2024 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Aff airs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 26 No. 1 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Kuts V.V., Oleshitsky A.V., Grechukhin A.N., Grigorov I.Y. Investigation of changes in geometrical parameters of GMAW surfaced specimens under the infl uence of longitudinal magnetic fi eld on electric arc....................................... 6 Saprykina N.А., Chebodaeva V.V., Saprykin A.А., Sharkeev Y.P., Ibragimov E.А., Guseva T.S. Optimization of selective laser melting modes of powder composition of the AlSiMg system................................................................. 22 Gubin D.S., Kisel’ A.G. Features of calculating the cutting temperature during high-speed milling of aluminum alloys without the use of cutting fl uid............................................................................................................................................. 38 EQUIPMENT. INSTRUMENTS Borisov M.A., Lobanov D.V., Zvorygin A.S., Skeeba V.Y. Adaptation of the CNC system of the machine to the conditions of combined processing...................................................................................................................................... 55 Nosenko V.A., Bagaiskov Y.S., Mirocedi A.E., GorbunovA.S. Elastic hones for polishing tooth profi les of heat-treated spur wheels for special applications..................................................................................................................................... 66 Podgornyj Y.I., Skeeba V.Y., Martynova T.G., Lobanov D.V., Martyushev N.V., Papko S.S., Rozhnov E.E., Yulusov I.S. Synthesis of the heddle drive mechanism....................................................................................................... 80 MATERIAL SCIENCE Ragazin A.A., Aryshenskii V.Y., Konovalov S.V., Aryshenskii E.V., Bakhtegareev I.D. Study of the eff ect of hafnium and erbium content on the formation of microstructure in aluminium alloy 1590 cast into a copper chill mold............................................................................................................................................................................ 99 Zorin I.A., Aryshenskii E.V., Drits A.M., Konovalov S.V. Study of evolution of microstructure and mechanical properties in aluminum alloy 1570 with the addition of 0.5 % hafnium........................................................................... 113 Karlina Y.I., Kononenko R.V., Ivantsivsky V.V., Popov M.A., Deryugin F.F., Byankin V.E. Relationship between microstructure and impact toughness of weld metals in pipe high-strength low-alloy steels (research review)..................... 129 Patil N.G., Saraf A.R., Kulkarni A.P Semi empirical modeling of cutting temperature and surface roughness in turning of engineering materials with TiAlN coated carbide tool................................................................................. 155 Sawant D., Bulakh R., Jatti V., Chinchanikar S., Mishra A., Sefene E.M. Investigation on the electrical discharge machining of cryogenic treated beryllium copper (BeCu) alloys........................................................................................ 175 Karlina A.I., Kondratiev V.V., Sysoev I.A., Kolosov A.D., Konstantinova M.V., Guseva E.A. Study of the eff ect of a combined modifi er from silicon production waste on the properties of gray cast iron................................................. 194 EDITORIALMATERIALS 212 FOUNDERS MATERIALS 223 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Study of evolution of microstructure and mechanical properties in aluminum alloy 1570 with the addition of 0.5 % hafnium Igor Zorin 1, 2, a, *, Evgenii Aryshenskii 1, 2, b, Aleksandr Drits 1, c, Sergey Konovalov 1, 2, c 1 Samara National Research University named after S.P. Korolev, 34 Moskovskoe Shosse, Samara, 443086, Russian Federation 2 Siberian State Industrial University, 42 Kirova str., Novokuznetsk, 654007, Russian Federation a https://orcid.org/0000-0001-9349-2494, zorin.ia@ssau.ru; b https://orcid.org/0000-0003-3875-7749, arishenskiy_ev@sibsiu.ru; c https://orcid.org/0000-0002-9468-8736, alexander.drits@samara-metallurg.ru; d https://orcid.org/0000-0003-4809-8660, konovalov@sibsiu.ru Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2024 vol. 26 no. 1 pp. 113–128 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.1-113-128 ART I CLE I NFO Article history: Received: 18 October 2023 Revised: 25 October 2023 Accepted: 20 November 2023 Available online: 15 March 2024 Keywords: Aluminum alloys Scandium Hafnium Microstructure Intermetallic compounds Mechanical properties Heat treatment Transmission microscopy Funding The study was supported by a grant of the Russian Science Foundation, project No. 22-29-01506, https://rscf. ru/project/22-29-01506/ Acknowledgements The work was carried out using the equipment of the Center for Collective Use “Technologies and Materials of the National Research University “BelSU”. ABSTRACT Introduction. Aluminum alloys are in high demand with the aerospace industry. From the viewpoint of various performance characteristic combinations, high-magnesium aluminum alloys with the addition of transition metals, such as Zr and Sc, are among the most future-oriented alloys. Alloy 1570 is one of the most popular in this group. Recent studies demonstrated the positive eff ect of 0.5 % hafnium addition on as-cast structure. Study objective is to study the eff ect of the addition of 0.5% hafnium on the structure and properties of aluminum alloy 1570 during thermomechanical treatment. The study addresses the eff ect of cold rolling, homogenization, and recrystallization annealing on mechanical properties and microstructure of the specimens from alloy 1570 and similar alloy with 0.5 wt. % hafnium addition. Study methodology: for the study, ingots were cast from alloy 1570 with and without additions of 0.5 wt. % of hafnium. The resulting ingots were homogenized for 4 h at 440 °С, followed fi rst by hot rolling and then cold rolling. Cold-rolled specimens were annealed at temperatures 340 °С to 530 °С with a holding time of 3 hours. The homogenized, cold-rolled, and annealed specimens were examined using transmission and light microscopy. In addition, homogenized and cold-rolled specimens were subjected to uniaxial tensile tests to determine the mechanical properties of the studied alloy. Results and discussion. It is revealed that in an alloy containing hafnium, after homogenization annealing, there is a slight decrease in the average particle size and an increase in its total proportion in comparison with alloy 1570. In general, 0.5 % hafnium addition does not signifi cantly aff ect the mechanical properties. The number of nanoparticles in both alloys increases, as does the yield strength compared to the as-cast state. When heated, both alloys demonstrate an increase in plasticity and a decrease in strength characteristics. Studies of the annealing eff ect on the grain structure of the studied alloys showed that hafnium increases the tendency of alloy 1570 to recrystallize. However, additional research is required to determine the reasons for this phenomenon. For citation: Zorin I.A., Aryshenskii E.V., Drits A.M., Konovalov S.V. Study of evolution of microstructure and mechanical properties in aluminum alloy 1570 with the addition of 0.5 % hafnium. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 1, pp. 113–128. DOI: 10.17212/1994-6309-2024-26.1-113-128. (In Russian). ______ * Corresponding author Zorin Igor A., Master’s Degree student Samara National Research University named after S.P. Korolev, 34 Moskovskoe Shosse, 443086, Samara, Russian Federation Tel.: +7 927 731-03-85, e-mail: zorin.ia@ssau.ru
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Introduction Aluminum alloys are widely used in various industries due to its high corrosion resistance, weldability, and low density [1–5]. In particular, in the aerospace industry, Al-Mg alloys, known in foreign literature as 5XXX series of alloys, are one of the most common groups of aluminum alloys [6, 7]. These alloys are in high demand because the addition of magnesium enhances its mechanical properties through solid solution strengthening [8, 9]. The addition of scandium further improves its mechanical properties [10–12]. Scandium has low solubility in supersaturated aluminum solid solution, with a solubility of 0.35 % at equilibrium conditions and 655 °C [13]. However, if the cooling rate is high enough after casting, excess scandium can be dissolved in the aluminum matrix. Heating the alloy between 250 °C and 350°C causes the supersaturated solid solution to decompose and leads to the precipitation of Al3Sc, which has a spherical morphology with a radius ranging from 2 to 20 nm [14–16]. These particles have an L12-type lattice and minimal mismatches with the aluminum matrix, which ensures its coherence. Such nanoparticles provide strengthening, which occurs due to particles intercepting by dislocations. The strengthening eff ect is based on the Orowan mechanism when the nanoparticle sizes range from 1.5 to 4 nm [17–19]. Moreover, scandium is a potent structure modifi er, and its refi nement capability is due to the L12 structure of primary intermetallic compound Al3Sc formed in the liquid phase and the minimal mismatch between crystalline lattice and aluminum solid solution [13, 14]. It is worth noting that the modifying eff ect appears only when the scandium concentration reaches 0.6%, when primary Al3Sc particles begin to form in the liquid [14]. However, as the temperature rises to 400 °C, scandium nanoparticles formed during solid solution decomposition start coagulating and increasing in size. When particle reaches a critical diameter of 30–40 nm, it loses its coherence, and the strengthening eff ect disappears [16]. This is a signifi cant limit for the use of scandium alloy. For example, it reduces the temperature of the homogenization and hot deformation processes, which inevitably aff ects its effi ciency and leads to higher energy costs [20]. Minor zirconium additions are used to improve the thermal stability of Al3Sc-type nanoparticles [21]. Zirconium can form a shell around Al3Sc particles as it is partially soluble in it. This shell inhibits the growth of Al3Sc nanoparticles at elevated temperatures as zirconium has a lower diff usion coeffi cient than scandium [22]. Additionally, zirconium reduces scandium concentration, which is needed to form primary Al3Sc intermetallic compounds in the liquid phase, contributing to the as-cast structure modifi cation [23, 24]. One of the classic aluminum alloys with a high Mg content and Sc and Zr additives, successfully used in industry, is 1570 alloy [25, 26]. However, even with the presence of zirconium, Al3Sc particles still do not have suffi cient thermal stability to retain its size during high-temperature homogenization and further hot deformation [20]. One way to solve this problem is to add hafnium to the 1570 alloy. Hafnium has an even lower diff usion coeffi cient than zirconium [22] and partially dissolves in Al3Sc particles [27], creating thermal stabilizing shells around it [22]. The joint addition of hafnium and zirconium is highly eff ective for thermal stabilization of Al3Sc particles [28, 29]. The eff ect of combined hafnium and zirconium additions on the thermal stabilization of Al3Sc particles has been mainly studied for lean aluminum alloys, but aluminum alloys with a high Mg content have several specifi c features. Firstly, magnesium slightly accelerates the decomposition kinetics of aluminum solid solution supersaturated with scandium [30]. Secondly, it stimulates an increase in the critical size of nanoparticles, after which its coherence is lost [13, 31]. Therefore, studying the hafnium eff ect on Al3Sc particles in commercial aluminum alloys with a high Mg content is of utmost interest. The eff ect of adding 0.5 % hafnium to the 1570 alloy was studied in the as-cast state. It was found that 0.5 % hafnium addition stimulates as-cast structure modifi cation and leads to the complete termination of discontinuous decomposition of aluminum solution supersaturated with scandium [32, 33]. Discontinuous decomposition during ingot cooling down is a negative process when Al3Sc needle-shaped precipitates are formed [34–36]. Such particles are usually semi-coherent to the aluminum matrix and do not contribute signifi cantly to strengthening compared to equiaxed dispersed phases formed during heat treatment. After discontinuous decomposition, the aluminum supersaturated solid solution contains no scandium, which is needed for Al3Sc nanoparticle formation during subsequent thermomechanical treatment [12, 34].
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Considering the ability of 0.5 % hafnium to inhibit discontinuous decomposition, it is worth investigating its eff ect on the microstructure and mechanical properties of the 1570 alloy in the as-cast state and during subsequent thermomechanical treatment. Most 1570 alloy products are thin-walled and are produced from sheets that are supplied in annealed or cold-rolled states, depending on the required properties. Therefore, it makes sense to study the eff ect of 0.5 % hafnium on the microstructure and mechanical properties of the 1570 alloy after these types of treatment. To achieve the study objective, the following tasks need to be addressed: studying nanoparticle formation during 1570 alloy homogenization annealing, as its size and number will dictate alloy structure and properties during subsequent thermomechanical treatment stages. Additionally, the eff ect of 0.5 % hafnium on mechanical properties and grain structure needs to be studied for cold-rolled and annealed states. Study methodology The study focused on the 1570 aluminum alloy and its version with the addition of 0.5 % hafnium. These alloys were chosen based on its chemical composition, which is listed in Table 1. The production of these alloys was carried out in the lab induction furnace UI-25P, and the resulting ingots had dimensions of 20×40×400 mm. Molten metal was cast into a steel chill mold with water cooling at a melt temperature of 720–740 °C. Ta b l e 1 Chemical composition of the studied alloys, % Alloy Al Si Fe Mn Mg Ti Zr Sc Hf 1570 base 0.17 0.26 0.4 6.1 0.03 0.07 0.25 – 1570 0.5Hf base 0.15 0.32 0.42 6.36 0.01 0.04 0.2 0.52 Specimens preparation technology Ingots casting Ingots weighing 5 kg each were produced; with 3 ingots cast per each chemical composition. The charge stock used included A85 grade aluminum, MG90 grade magnesium, and alloying compounds such as Al-Sc2, Al-Zr5, Al-Hf2, and Mn90Al10 tablets. The content of elements was determined according to various standards such as GOST 25086, GOST 7727, GOST 3221, ASTM E 716, and ASTM E 1251 using an atomic emission spectrometer ARL 3460. The required concentration of stock materials, including hafnium, was calculated theoretically since there is a currently no GOST covering hafnium additive. After solidifi cation, the ingots were removed from the mold and water chilled. Homogenization annealing Homogenization annealing at 440 °C for 4 hours dissolves non-equilibrium eutectic and improves chemical homogeneity in aluminum solid solution. Uniaxial tensile tests were conducted on homogenized specimens. Rolling The studied specimens underwent a rolling process. It is important to note that the commercial production of 1570 alloy sheets involves hot rolling above the recrystallization temperature followed by cold rolling. The laboratory rolling process used the same practice in order to produce sheet material. Initially, the specimens were hot rolled in a Duo reversing mill. The process reduced the thickness from 40 mm to 5 mm at a temperature of 440 °С and a roll rotation speed of 3 m/min. After every three passes, the ingots
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 were heated back up to the initial rolling temperature. The overall reduction percentage was 88 %. It is worth mentioning that the hot rolling temperature was the same as the homogenization temperature. This is because a higher temperature may cause particle coagulation, at least in the alloy without hafnium content. Lower temperatures may result in a loss of plasticity [20]. Rolling a small ingot that has already been heated after homogenization, including its heating in the furnace, takes no more than 30 minutes. The microstructure and properties of the alloy were not examined after this operation since it was not a fi nishing operation, and short-term heating did not signifi cantly aff ect Al3Sc particles. After reaching a thickness of 5 mm, the tapes underwent cold rolling to 2 mm thick. The percentage of reduction during cold rolling was 95 %. Cold rolled tape annealing The cold-rolled tape from the tested alloys was annealed after rolling to examine how the hafnium content aff ects the recrystallization process. Furthermore, an additional series of annealing was conducted on the cold-rolled tape to investigate the mechanical properties of the alloy (Table 2). Ta b l e 2 Annealing modes of cold-rolled tape Annealing for recrystallization verifi cation Annealing for mechanical properties analysis 470 °C – 3 hours 340 °C – 3 hours 500 °C – 3 hours 440 °C – 3 hours 530 °C – 3 hours 470 °C – 3 hours 550 °C – 3 hours 530 °C – 3 hours It is worth noting that the annealing temperature for high-magnesium alloy can be chosen from a wide range of temperatures (340 to 530 °C), depending on the required mechanical properties level and the desired combination of strength and plastic properties, as well as the contents of scandium, zirconium, and hafnium. This is precisely why these temperature values were chosen for the present study. Methods for studying the microstructure and mechanical properties of specimens Transmission electron microscopy The fi ne structure of the specimens was analyzed using a JEOL analytical transmission electron microscope from Japan. The microscope had a 200 kV accelerating voltage and an INCA attachment for EDX analysis from Oxford Instruments in the UK. To achieve precision positioning of the foil specimen, a 2-axes rotation holder was used, allowing it to be tilted ±30° along each axis. For particle transmission electron microscopy (TEM) analysis, standard procedures were followed. This included preparing two 500 μm thick foil specimens, further thinning it mechanically to 120 μm, and electrolytic thinning [29]. A total of fi ve thin foil specimens were prepared for TEM analysis. For the examination of Al3Sc particles, a specimen was placed in the zone axis, and an electron diff raction pattern was taken. During the examination, a weak superstructure refl ection from the (011) α plane was detected. This method allowed the acquisition of dark-fi eld images (DF), which helped count the visible particles. To determine the particle size and density, we used a Digitizer software module. We assessed the average particle size and its fraction by studying fi ve diff erent fi elds of view for each condition. Optical microscopy Optical microscopy was performed using an Axiovert microscope, and the average grain size after recrystallization was determined using the secant method.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Mechanical properties The alloys underwent uniaxial tensile tests at room temperature using a Zwick/Roell universal testing machine in accordance with ISO 6892-1, GOST 1497-84, and GOST 11150-84 standards. At least 5 tenfold round specimens with a 10 mm diameter were tested for each analyzed state. The data from the tests performed after the specifi c specimens production process stage is presented in Table 3 below. Ta b l e 3 Technological chain of the specimens’ research Process chain stage Homogenized material Cold rolled material Test TEM Mechanical properties Mechanical properties Optical microscopy Results and discussion The structure of the as-cast material after homogenization annealing for 4 hours at 440 °C is shown in fi gure 1. b Fig. 1. Fine structure of a cast billet made of 1570 alloy after its homogenization annealing at 440 °C for 4 hours: a) microdiff raction in the zone of axis [001] α; b) DF а
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 The average size of the particles in the specimen is 11.4 nm with a density of f = 2.2×1010 cm−2 as analyzed through transmission electron microscopy (DF) in fi g. 1. The homogenization annealing process resulted in particles mostly ranging from 1.6 nm to 13.3 nm, indicating a prevalence of fi ne phases in the specimen. However, there are also some coarse particles exceeding 25 nm in size. In fi gure 1 a one can clearly observe superstructural refl ections L12; this fact, according to [32], indicates the presence of Al3Sc particles in aluminum alloys containing scandium. The size range of particles in the 1570 0.5Hf alloy is dominated by particles that are between 5.2 and 14.5 nm in size (as shown in fi gure 2, b). However, particles larger than 25 nm are also identifi ed in DF images. The average particle size in this alloy is 10.5 nm, with a particle distribution density of 2.6×1010 cm−2. It is observed that the non-uniformity of particle distribution inside the grain volume was reduced when compared to the 1570 alloy. Although superstructure refl ections are present (as shown in fi gure 2, a), it is relatively weak compared to the original 1570 alloy. This means that a smaller amount of dispersed phases is formed. It is important to note that previous studies showed that in the as-cast 1570 alloy, discontinuous decomposition resulted in the formation of some 7–10 nm Al3Sc nanoparticles. However, discontinuous decomposition is not observed in the alloy with hafnium addition, and Al3Sc particle formation does not occur. By comparing the study results for the as-cast state and after homogenization with the data presented in the paper [29], it can be concluded that heating at 440 °С for 4 hours increases the general number of nanoparb Fig. 2. Fine structure of the cast billet made of alloy 1570 0.5Hf after its homogenization annealing at 440 °C for 4 hours: а) microdiff raction in the zone of axis [001] α; b) DF а
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 Fig. 3. Mechanical properties of studied as-cast alloys after homogenization annealing at 440°C – 4 hours ticles in the 1570 alloy. In an alloy with hafnium additives, all particles are formed during heat treatment. However, fi nally, after thermal treatment, Al3Sc nanoparticles in both alloys generally have approximately equal size and number. The 1570 aluminum alloy and its modifi ed version with 0.5 % hafnium addition exhibit almost identical strength in a homogenized state (fi gure 3). After analyzing post-heat treatment strength properties and as-cast state data from the paper [33], it is evident that heating has minimal eff ect on ultimate strength (fi gure 3), showing only a slight increase. The infl uence of particles on the increase in yield stress is explained primarily by the degree of infl uence of dispersed phases. The greater the number of particles of the dispersed phase released, the more diffi cult it is for dislocations to move along planes and, as a consequence, when the movement of dislocations is diffi cult, the yield strength increases. On the other hand, several factors such as metal porosity, presence of coarse intermetallic compounds, etc., aff ect the ultimate strength. Therefore, the ultimate strength remains at the same level. The homogenized state of both alloys exhibits similar strength parameters primarily associated with similar particle numbers and sizes. Figure 4 shows the eff ects of cold rolling and annealing at diff erent temperatures on the alloys. During cold rolling, the alloys form a fi ber structure (as shown in fi gure 4), and black dots visible in the grain structure depict coarse intermetallic compounds. The size, chemical composition and morphology of these alloys have been already studied [32, 33]; therefore, its analysis by scanning microscopy methods was not carried out in the current paper. At temperatures up to 440 °С, cold-rolled sheets maintain a non-recrystallized structure. This shows that the Al3Sc particles effi ciently inhibit the recrystallization process [37]. In the 1570 alloy, new grain nuclei only appear during annealing at 500 °С for 3 hours, and only with an increase in annealing temperature to 530 °С, a mixed structure with an approximate ratio of 1:1 can be observed. The alloy with 0.5 % hafnium addition is more susceptible to recrystallization. After annealing at 500 °С and soaking for 3 hours, a mixed structure with predominantly recrystallized grains is observed in the 1570 alloy with 0.5 wt% Hf. If the annealing temperature is further increased to 530 °С, a fully recrystallized structure is observed in the alloy containing 0.5 % hafnium. It is worth noting that in hafnium-containing alloys, the resultant microstructure has a smaller grain size due to recrystallization than the as-cast state. The causes of accelerated recrystallization in the 1570 alloy with hafnium addition require further investigation.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 a b c d Fig. 4. Microstructure of sheets after cold rolling with 90 % deformation and subsequent annealing of alloys 1570 (left) and 1570-0.5Hf (right): a) after cold rolling; b) after annealing at 470 °C for 3 hours; c) after annealing at 500 °C for 3 hours; d) after annealing at 530°C for 3 hours It should also be emphasized that recrystallization in hafnium-containing alloys should not be interpreted as an entirely negative process. The occurrence of a super-fi ne as-cast structure and the possibility of modifi cation during recrystallization can create conditions for obtaining grain with suffi cient sizes for superplastic fl ow. This is facilitated by the fact that, according to [32], hafnium additives contribute to the modifi cation of the cast structure in 1570 alloy. In the case of recrystallization after annealing at 530 °C for 3 hours, the grain size is 25 μm. Therefore, by increasing the overall degree of cold rolling in an alloy containing hafnium and introducing several intermediate recrystallization annealing, each of which will cause a refi nement of the structure, it is possible to achieve an average grain size of up to 8 μm. This grain size is suffi cient for superplastic fl ow in aluminum alloys with high magnesium content [38]. Figure 5 depicts the mechanical properties of the alloys after undergoing diff erent treatment modes, as shown in fi gure 4. The yield strength values of the studied alloys are generally similar (fi gure 5, а). In both cases, the yield strength of the alloys dropped from 460 MPa in the cold-rolled state to around 150 MPa after being annealed at the highest temperature of 530 °С and soaked for 3 hours. This decrease is due to the recovery and dislocation annihilation that occur during the low-temperature thermal treatment. Consequently, the strength parameters after annealing at 530 °С and 3 hour soaking are almost the same as the parameters observed in the as-cast state [33]. As the temperature and soaking time increase, the ultimate strength of both alloys changes in a manner similar to the yield strength values (fi gure 5, b). The plasticity of the alloys increases, which is related to a decrease in the number of linear defects and hardening degree (fi gure 5, c). In general, the 15700.5Hf alloy has lower plasticity than the original alloy. This is due to the formation of coarse primary Al3Sc intermetallic compounds caused by the hafnium content in 1570-0.5Hf [32]. Thus, the hafnium content does not have a signifi cant eff ect on either the number of Al3Sc nanoparticles or the increase in strength properties caused by it. Separately, it is worth saying that the past recrystallization does not have a signifi cant eff ect on the strength properties. This is explained by the fact that in 1570 alloy the grain remains deformed even during
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 c Fig. 5. Mechanical properties of 1570 and 1570–0.5Hf sheets: а) yield strength, σ0.2, MPa; b) ultimate strength, σв, MPa; c) relative elongation, δ, % a b annealing at a temperature of 530 °C (fi gure 4), which improves the mechanical properties. On the other hand, in an alloy with hafnium after recrystallization, a decrease in the average grain size is observed, which also has a benefi cial eff ect on strength. Conclusion After conducting the study, the following conclusions can be made: 1. The TEM results after homogenization showed that annealing in a 1570-0.5Hf alloy led to a reduction in the average size of nanoparticles and an increase in its overall portion compared to the 1570 alloy. However, this does not have a signifi cant eff ect on the diff erence in mechanical properties in homogenized states. 2. The addition of 0.5 wt. % hafnium content increases the tendency of the 1570 alloy to recrystallize during high-temperature treatment. However, further studies are required to understand the causes of this eff ect. Regardless of whether there is recrystallization in the 1570-0.5Hf alloy, both studied alloys demonstrate similar strengthparameters associatedwith the average grain size decrease after recrystallization. Recrystallization can also have an additional modifying eff ect on the size of the cast structure. References 1. Kaibyshev R., Avtokratova E., Sitdikov O. Mechanical properties of an Al-Mg-Sc alloy subjected to intense plastic straining. Materials Science Forum, 2010, vol. 638–642, pp. 1952–1958. DOI: 10.4028/www. scientifi c.net/MSF.638-642.1952.
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