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The peculiarities of the superplasticity effect of the aluminium Al-Zn-Mg-Cu-Zr system alloy with two types of initial grain structure are considered. For the first type of structure, the large grains are predominant, and submicrocrystalline grains take up less volume. Another type of grain microstructure is that of large grains, rounded by small submicrocrystalline grains, which occupy a significantly larger relative volume. Samples with both types of microstructure exhibit superplastic properties, however, the range of flow stresses and strain rates in which the alloy samples are superplastic is much wider for a microstructure where submicrocrystalline grains predominate. For both types of microstructure, deformation processes are mainly localized in those volumes of samples where submicrocrystalline grains were concentrated. However, large grains change their shape during superplastic deformation. The reason for this may be the manifestation of the hydrodynamic flow during the process of deformation.

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З метою підвищення показників надпластичности алюмінійового стопу системи Al-Zn-Mg-Cu-Zr було проведено його термомеханічне оброб-лення, яке включало відпал і вальцювання зразків. Це уможливило ство-рення в стопі замість бімодальної структури однорідної субмікрокриста-лічної структури, хоча і з переважаючою кількістю малокутових меж зе-рен. Однак, таке оброблення дало змогу значно підвищити показники надпластичности даного стопу, зокрема, видовження до зруйнування зро-сло майже в два рази.

The article discusses the effect of preliminary high-temperature homogenization annealing on the microstructural changes in alloy 1933 and their correlation with the superplasticity and microsuperplasticity of the alloy. The research shows that annealing of alloy 1933 at 520 °C for 2 h leads to the dissolution and melting of the -phase particles (MgZn2), T-phase particles (Mg3Zn3Al2), and S-phase particles (Al2CuMg), which are present in the initial microstructure of the alloy. The annealing results in a redistribution of the crystallographic orientations of the crystallites of the -solid solution based on aluminum and the removal of internal microstresses in the volume of the alloy. It is found that preliminary heat treatment slightly affects the mechanical behavior of alloy 1933 under conditions of superplastic deformation. Fibrous structures, the process of the formation and development of which is called microsuperplasticity, are observed both in the samples that have not undergone preliminary homogenization annealing and in the annealed samples. The concentration of Mg atoms in the fibers is higher than their average concentration in the alloy. At the same time, the concentration of Zn and Cu atoms in the fibers is almost two times lower than their concentration in the alloy. The authors propose the mechanism of fiber formation and development, where fiber nucleation is caused by viscous flow of the material formed by melting of -magnesium enriched solid solution based on alumina, and further fiber growth is carried out by the complex of deformation mechanisms operating during the superplastic flow of the alloy.