1151 ISSN 1063-7842, Technical Physics, 2019, Vol. 64, No. 8, pp. 1151–1154. © Pleiades Publishing, Ltd., 2019. Russian Text © The Author(s), 2019, published in Zhurnal Tekhnicheskoi Fiziki, 2019, Vol. 89, No. 8, pp. 1219–1222. Inelasticity and Nanostructured Dislocation Deformation of Aluminum–Silicon Alloy with a Supermodified Eutectic Structure S. P. Nikanorov a, *, B. K. Kardashev a , V. N. Osipov a , V. V. Kaminskii a , and N. V. Sharenkova a a Ioffe Institute, St. Petersburg, 194021 Russia *e-mail: s.nikanorov@mail.ioffe.ru Received February 28, 2019; revised February 28, 2019; accepted March 11, 2019 Abstract—Young’s modulus and the logarithmic decrement of oscillations at a frequency of ~100 kHz as well as the subgrain size and residual stresses in the strontium modified alloy of aluminum with 15 wt % silicon have been studied. The alloy was obtained with a solidification rate of 1 mm/s at the shifted eutectic point. The dependence of inelastic dislocation deformation on the applied oscillating stress has been obtained and analyzed. The effect of strontium modification on the microstrain diagram can be accounted for by transfor- mation of the lamellar fiber structure of eutectic silicon into a superfine fiber structure. DOI: 10.1134/S1063784219080164 Cast aluminum–silicon alloys are widely used for construction purposes in building and car production, naval and air industries, and as parts and items of internal combustion and diesel engines. The reasons is the high specific strength of alloys with respect to their weight, high thermal conductivity, and high corrosion and wear resistance at a low thermal expansion coeffi- cient. At present, the effect of different chemical ele- ments on the microstructure of eutectic (11–12.5 wt % Si) and hypereutectic alloys are intensively studied. An increase in the grain size leads to an increase in the strength and some unpredictable influence on other properties. It is known that a substantial increase in the solidi- fication rate causes a decrease in the microstructural grain size as well as an appreciable increase in porosity. It was shown in [1] that an increase in the solidifica- tion rate led to a simultaneous shift of an alloy eutectic point towards an increase in the silicon content and corresponding increase in the maximum time tensile strength. The Al–15 wt % Si alloy in the eutectic point shifted towards higher concentrations was obtained in [2] at moderately increased rate of directed solidifica- tion (1 mm/s). The alloy was characterized by a fiber eutectic structure without initial silicon crystals, which corresponds to a rating of 5 of the structure according to the American Foundry Society (AFS) [3], and increased ultimate strength. When 0.01 wt % of Sr was added, the supermodified eutectic structure with high strength and record high plasticity, which corresponds to rating of 6 in the AFS system, was obtained. However, other physical and mechanical properties of that unusual cast alloy with the hypereu- tectic composition and completely eutectic structure without silicon were not studied. In this study, the microstructure, residual stresses, dislocation defects of Young’s modulus, internal fric- tion, as well as the inelastic deformation diagram of Al–15 wt % Si–0.01 wt % Sr alloy with the supermod- ified structure have been studied. The alloy was obtained by directed crystallization when pulling a tape with dimensions of 1000 × 15 × 3 mm from melt through an air-cooled former by the Stepanov method [1]. The melt temperature was 660°C, the pulling rate was 1 mm/s. The temperature gradient was about 12 K/mm. The initial materials had a purity of 99.9 wt % for Al and Sr and 99.8 wt % for Si. The stud- ied samples in the form of rods with a length of 27 mm and cross-section of 6 mm 2 were cut from a crystal- lized tape by the electric-spark method. The studied alloy consisted of α-Al solid solution of silicon in aluminum and silicon crystals. The X-ray diffraction analysis showed that α-Al was character- ized by a subgrain structure. The subgrain size in α-Al solid solution was determined by sizes of regions of X-ray coherent scattering. X-ray diffraction analysis was carried out using the DRON-2 diffractometer goniometer based on the diffraction patterns (θ–2θ scanning) obtained in K α -radiation of a copper anode. The size of coherent scattering regions (CSRs) was SOLID STATE