ИСТИНА

We experimentally investigated the nanostructuring effect on the elastic properties of aluminum alloy AMg6 (Al–Mg–Mn system). The n-AMg6 nanostuctured samples were prepared from a commercial polycrystalline alloy by refinement and homogenization a mixture of small chips of the alloy with the addition of 0.3 wt.% of C60 fullerite in a planetary mill. The resulting product consists of 200-500-micron agglomerates of nanoparticles. The сoherent scattering length (CSL) distribution in the powdered samples showed the mean nanoparticle size of ~ 40–60 nm. The process was conducted in a protected Ar-atmosphere; additional studies confirmed the absence of oxygen and the corresponding insertion of aluminum oxidation. Then, the milled nanopowder was pre-compacted in a cylindrical mold with a 180 mm diameter at a 250 0C temperature and a 200–300 MPa pressure. The resulting compact (preform) was subjected to extruding at a temperature of 300 0C with a reduction of cross-sectional area at least 4 times (in this case to a 90 mm diameter). The recrystallization process is hindered by grain boundary modification with a C60 fullerite; the latter plays the role of a compacted samples’ stabilizer. For the experiments, 9 samples in a cuboid shape of 20´20´40 mm size were cut from the central and peripheral parts of the n-АМg6 ingot. Three samples of the same size were made of AMg6 billet alloy. The velocities of longitudinal VL and shear VT BAWs defined with high precision allowed, in the approximation of an isotropic solid, to compute the second-order elastic constants (SOEC) Cij, the 2nd-order compliance modules Sij, Young's modulus E, bulk modulus K, and Poisson's ratio  in the samples [1]. Errors in the determination of these coefficients do not exceed 2%. To characterize the nonlinear elastic properties of solids, the third-order elastic constants (TOEC) are used. They determine the anharmonic properties of the crystal lattice, such as thermal expansion, ultrasound attenuation, and efficiency of the nonlinear interaction of elastic waves in solids. The TOECs were determined with a Thurston-Brugger method [2]. To do this, the relative changes in velocity of bulk waves depending on the applied uniaxial compression were experimentally measured in the test samples. Comparison of the determined SOECs in the АМg6 and n-АМg6 alloys showed that they are equal within the measurement errors. However, the values of TOECs vary considerably in these alloys. A similar behavior of TOEC and SOEC were previously found by us in aluminum alloy B95 and B95/Nanodiamond Composite [3]. This indicates that the TOEC is more sensitive to the composition, structure and stoichiometry of the material than the SOEC. The studies were supported by the Russian Science Foundation (project № 14-22-00042) and by the Ministry of Education and Science of the Russian Federation (grant UI RFMEFI57714X0090). References 1. R. Truell, Ch. Elbaum, and B. Chik, Ultrasonic Methods in Solid State Physics (Academic, New York, 1969). 2. R. N. Thurston and K. Brugger, Phys. Rev. [Sect.] A133, 1604 (1964). 3. A. I. Korobov, V. M. Prokhorov, and D. M. Mekhedov. Physics of the Solid State. 55, 8 (2013).