Structural evolution of AL25 alloy during hot deformation

This article addresses improvement of the mechanical properties of Al–Si alloys, in particular the complex-alloyed silumin AL25, by hot deformation. The aim of the study was to assess the effect of hot-deformation temperature and strain rate on the grain size of the aluminum-based solid-solution matrix, the size of silicon and intermetallic particles, and the amount of defects in the form of microcracks and micropores in AL25 alloy. AL25 alloy billets (composition, wt. %: 12.0 Si, 3.0 Cu, 1.0 Mg, 1.2 Ni, 0.7 Mn, 0.7 Fe, balance Al) were produced by permanent-mold casting. Microstructural analysis was performed using a Neophot-2 metallographic microscope and a Tescan Mira 3LHM scanning electron microscope. The billets were deformed by upsetting between f lat dies in an isothermal die on a hydraulic press and were tensile-tested at temperatures of 350–500 °C over a strain-rate range of 10^–4–10¹ s^–1 using an Instron universal electromechanical testing machine. To evaluate the effect of deformation on the structure and properties of the alloy, the initial billets were deformed at 400–500 °C and strain rates of 10^–4 and 10^–2 s^–1. Heat treatment was carried out according to the following schedule: quenching from 515 °C and aging at 210 °C for 10 h. It was shown that, after all deformation conditions followed by quenching and aging, the solid-solution structure was fine grained and recrystallized, with an average grain size of 7–15 μm. Recrystallization occurred during heating prior to quenching when deformation was performed at 350–480 °C, and also before reheating, as observed after deformation at 500 °C. The grain structure of the solid solution was heterogeneous throughout the alloy volume because of the nonuniform distribution of silicon particles and intermetallics. The smallest grains were observed in eutectic colonies, where the alloy exhibited a microduplex-type structure. Hot upsetting of AL25 alloy caused fragmentation of silicon particles and intermetallics. This process was accompanied by crack initiation within the particles; the cracks then widened, separating the newly formed fragments. Cracks in eutectic silicon crystals and intermetallics formed at all deformation temperatures. In primary crystals, cracks were observed only at a high strain rate of – 10¹ с^–1. Fragmentation of silicon particles and intermetallics was governed mainly by the degree of deformation. The formation of defects in the form of microcracks and micropores also depended on temperature and degree of deformation. As the degree of deformation increased, the total area occupied by defects, their average area, and their total number increased. A correlation was established between alloy structure and mechanical properties. Optimal temperature–strain-rate conditions were determined that promoted microcrack healing of and increased long-term strength.

1. Trusov P.V., Ostanina T.V., Shveykin A.I. Evolution of the grain structure of metals and alloys under severe plastic deformation: multilevel models. PNRPU Mechanics Bulletin. 2022;(2):114—146. (In Russ.). https://doi.org/10.15593/perm.mech/2022.2.11

2. Zhao X., Meng J., Zhang C., Wei W., Wu F., Zhang G. A novel method for improving the microstructure and the properties of Al—Si—Cu alloys prepared using rapid solidification/powder metallurgy. Materials Today Communications. 2023;35:105802. https://doi.org/10.1016/j.mtcomm.2023.105802

3. Klassman E.Yu., Lutfullin R.Ya. Influence of the billet heating temperature before warm rolling on the structure and properties of titanium alloy VT22. Fundamental’nye problemy sovremennogo materialovedeniya. 2024;21(2): 205—211. (In Russ.). https://doi.org/10.25712/ASTU.1811-1416.2024.02.008

4. Lutfullin R.Ya. Formation of the structure and properties of titanium alloy in products made using superplastic deformation. Fundamental’nye problemy sovremennogo materialovedeniya. 2024;21(1):75—81. (In Russ.). https://doi.org/10.25712/ASTU.1811-1416.2024.01.009

5. Ganeev A.A., Valitov V.A., Mukhtarov Sh.Kh., Imayev V.M. Effect of pre-deformation and subsolvus heat treatment on microstructure and mechanical properties of a PM nickel superalloy. Materialia. 2025;42:102445. https://doi.org/10.1016/j.mtla.2025.102445

6. Mukhtarov S., Karyagin D., Ganeev A., Zainullin R., Shakhov R., Imayev V. The effect of forging and heat treatment variables on microstructure and mechanical properties of a re-bearing powder-metallurgy nickel base superalloy. Metals. 2023;13(6):1110. https://doi.org/10.3390/met13061110

7. Zainullin R.I., Mukhtarov Sh.Kh., Ganeev A.A., Shakhov R.V., Imayev V.M. Effect of hot forging on formation of a fine-grained structure and mechanical properties of a powder metallurgy nickel base superalloy. Letters on Materials. 2023;13(4s):414—419. https://doi.org/10.22226/2410-3535-2023-4-414-419

8. Khina B.B., Pokrovsky A.I., Zhang Shi-Hong, Xu Yong, Chen Da-Yong, Marysheva А.А. Effect of strain rate on the microstructure and mechanical properties of AA2B06-O aluminum alloy of the Al—Cu—Mg system. Russian Journal of Non-Ferrous Metals. 2021;62(5):545— 553. https://doi.org/10.3103/S1067821221050060

9. Timoshkin I.Y., Nikitin K.V., Nikitin V.I., Deev V.B. Influence of treatment of melts by electromagnetic acoustic fields on the structure and properties of alloys of the Al—Si system. Russian Journal of Non-Ferrous Metals. 2016; 57(5):419—423. https://doi.org/10.3103/S1067821216050163

10. Padalko A.G., Pyrov M.S., Karelin R.D., Yusupov V.S., Talanova G.V. Barothermal treatment, cold plastic deformation, microstructure and properties of binary silumin Al—8 at % Si. Russian Metallurgy (Metally). 2021;2021(9):1155—1164. https://doi.org/10.1134/S0036029521090123

11. Prudnikov A.N., Popova M.V., Prudnikov V.A. Effect of deformation on the structure and properties of silumins. Vestnik Sibirskogo gosudarstvennogo industrial’nogo universiteta. 2017;3(21):11—17. (In Russ).

12. Murashkin M.Yu., Zainullina L.I., Motkov M.M., Medvedev A.E., Timofeev V.N., Enikeev N.А. Microstructure, mechanical properties and heat resistance of AL30 piston alloy produced via electromagnetic casting. Materials Physics and Mechanics. 2024;52(1):81—94. http://dx.doi.org/10.18149/MPM.5212024_8

13. Золоторевский В.С., Белов Н.А. Металловедение литейных алюминиевых сплавов. М.: МИСИС, 2005. 376 с.

14. Белов Н.А., Савченко С.В., Белов В.Д. Атлас микроструктур промышленных силуминов. М.: Изд. дом МИСиС, 2009. 204 с.

15. Chen C.L., Tan M.J. Effect of grain boundary character distribution (GBCD) on the cavitation behavior during superplastic deformation of Al 7475. Materials Science and Engineering, A. 2002;338(1—2):243—252. https://doi.org/10.1016/S0921-5093(02)00083-7

16. Kral P., Dvorak J., Kvapilova M., Horita Z., Sklenicka V. Microstructure changes in superplastically deformed ultrafinegrained Al—3Mg—0.2Sc alloy. Letters on Materials. 2015;5(3):306—312. https:/doi.org/10.22226/2410-3535-2015-3-306-312

17. Yakovtseva O.A., Mikhailovskaya A.V., Kotov A.D., Medvedeva S.V., Irzhak A.V. Comparison of contributions of the mechanisms of the superplastic deformation of binary and multicomponent brasses. Physics of Metals and Metallography. 2020;121(6):582—589. https://doi.org/10.31857/S0015323020060182

18. Yakovtseva O.A., Kaboyi P.K., Irzhak A.V., Mikhailovskaya A.V. Effect of a small aluminum additive on the features and mechanisms of superplastic deformation of a Cu–Zn alloy with a microduplex structure. Physical Mesomechanics. 2023;26(3):62—71. (In Russ). https://doi.org/10.55652/1683-805X-2023-21-3-62

19. Yakovtseva O.A., Mikhailovskaya A.V., Kotov A.D., Mamzurina O.I., Portnoy V.K. Effect of the strain and strain rate on microstructure evolution and superplastic deformation mechanisms. Physics of Metals and Metallography. 2019; 120(1):87—94. https://doi.org/10.1134/S0031918X18110224

20. Li H., Liu X., Sun Q., Ye L., Zhang X. Superplastic deformation mechanisms in fine-grained 2050 Al—Cu— Li alloys. Materials (Basel). 2020;13(12):2705. https://doi.org/10.3390/ma13122705

21. Chokshi A.H. Grain boundary processes in strengthening, weakening, and superplasticity. Advanced Engineering Materials. 2020;22(1):1—9. https://doi.org/10.1002/adem.201900748

22. Korznikova G.F., Khalikova G.R., Mironov S.Yu., Aletdinov A.F., Korznikova E.A., Konkova T.N., Myshlyaev M.M. Superplastic behavior of fine-grainted Al—Mg—Li alloy. Physical Mesomechanics. 2022;25(2):47—55. (In Russ). https://doi.org/10.55652/1683-805X_2022_25_2_47