A. N. Petrova

Evolution of the structure of V95 aluminum alloy upon high-pressure torsion

The effect of the degree of deformation upon torsion under quasi-hydrostatic pressure on the structural and phase transformations in the V95 alloy has been studied by the methods of electron microscopy and X-ray diffraction. It has been found that, upon severe plastic deformation, a nanocrystalline structure with a hardness of 2.5 GPa is formed. The nanostructure with a minimum average grain size of 55–80 nm is being formed at e = 5.5–6.4. It has been shown that during dynamical strain aging at e ≥ 4.8, a hardening metastable phase MgZn2 precipitates from the supersaturated α solid solution, and the quantity of this phase increases with increasing degree of deformation.

Resistance of submicrocrystalline aluminum alloys to high-rate deformation and fracture after dynamic channel angular pressing

A comparative study of the deformation behavior of submicrocrystalline (formed by dynamic channel angular pressing) and coarse-grained commercial aluminum alloys (AMts and V95), and commercial aluminum A7 has been performed under impact compression conditions. Dynamic elastic limit (Hugoniot elastic limit) σHEL, yield strength Y, and spall strength σsp at a deformation rate of (1.2–3) × 105 s−1 were determined by analyzing the experimental velocity profiles of the free surface of samples. It has been found that the dynamic elastic limit and yield strength increase after all the materials studied have transformed into a submicrocrystalline state (crystallite size of 200–700 nm). Submicrocrystalline alloy V95 has the highest value of Y and submicrocrystalline aluminum A7 has the lowest one. The effect of grain size on spall strength is ambiguous. The values of σsp for submicrocrystalline alloys are 1.32–1.36 GPa. The submicrocrystalline V95 alloy and commercial A7 aluminum demonstrate a decrease in the spall strength, whereas the spall strength of the alloy AMts slightly increases with decreasing grain size.

Phase and structural transformations in the aluminum amts alloy upon severe plastic deformation using various techniques

The paper presents experimental data on the structure formation in the commercial aluminum alloy of grade AMts subjected to severe plastic deformation using dynamic channel-angular pressing and torsion under high quasi-hydrodynamic pressure in Bridgman anvils. The dependences of the structural characteristics and hardness on the degree, rate, and scheme of deformation have been analyzed.

Structure of an AMts aluminum alloy after high-pressure torsion in liquid nitrogen

We have presented the experimental data on the structure formation in commercial AMts aluminum-manganese alloy subjected to severe plastic deformation by torsion under high quasi-hydrostatic pressure in Bridgman anvils. The dependences of structural characteristics and hardness on the degree of deformation at room temperature and the temperature of liquid-nitrogen have been analyzed.

Comparing specific features of the structural formation of aluminum alloys during severe and intense plastic deformation

We compare the deformation behavior and specific features of the structural formation of two aluminum alloys, AMTs and V95, upon megaplastic (MPD) and severe plastic (SPD) deformation. It is established that upon SPD by dynamic channel angular pressing, a submicron crystalline structure is formed with grain sizes of 200 to 600 nm; and that upon MPD by high quasi-hydrostatic pressure shearing, a nanostructure is formed with grain sizes of 55 to 100 nm. The sequence of the phase and structure transition is established for an increase in the rate of deformation and velocity of the materials. Mechanisms of elastic energy relaxation are determined as a function of the extent of dislocation mobility.

Mechanical properties and energy dissipation in ultrafine-grained AMts and V95 aluminum alloys during dynamic compression

The thermomechanical characteristics of ultrafine-grained AMts and V95 aluminum alloys with an average crystallite size of 200–600 nm are experimentally studied during dynamic compression. The alloys are fabricated by dynamic channel angular pressing. It is found that the deformation history of the alloys and the initial characteristics of their structural state affect the subsequent plastic deformation and the dissipation of applied energy. The studies of the thermodynamics of deformation in combination with structural investigations before and after dynamic compression allowed us to reveal the main structural relaxation mechanisms in the materials during dynamic compression and to determine the dissipation abilities of various defect structures.

Influence of grain size on the mechanism of fracture of the aluminum alloy V95

Mechanical behavior and mechanisms of fracture of the ultrafine-crystalline (UFC) and the coarse-crystalline (CC) aluminum alloy V95 (Al-6.0 Zn-2.3 Mg-2.0 Cu-0.4 Mn (wt %)) manufactured via using severe plastic deformation, namely, by dynamic equal-channel angular pressing (DCAP), have been studied. It has been demonstrated that the UFC material exhibits improved mechanical properties in comparison with the CC analog. A correlation analysis of fracture surfaces and the determination of the Hurst exponent have made it possible to perform a comparative estimation of the uniformity of the fracture structure and of the fractions of ductile and brittle fractures in the samples with the structure-scale characteristics different in value.

Influence of megaplastic deformation on the structure and hardness of Al–Cu–Mg alloy after aging

Methods of electron microscopy and X-ray diffraction have been used to investigate structural and phase transformations in the aluminum alloy of grade A2024 (Al–4.5 Cu–1.37 Mg–0.61 Mn–0.07 Si–0.27 Fe–0.02 Zn–0.02 Ti (wt %)) after aging and deformation by shear under high quasi-static pressure. It has been shown that the combination of two-stage aging with megaplastic deformation leads to the refinement of the structure to a nanolevel and to strengthening of the alloy (to an increase in the microhardness to 3000 MPa). The values of true deformation at which the deformation-induced dissolution of the particles of the strengthening S phase occurs have been determined.

Measuring the nanohardness of commercial submicrocrystalline aluminum alloys produced by dynamic pressing

The nanohardness of submicrocrystalline aluminum alloys produced by dynamic channel angular pressing has been measured. It has been shown that the nanohardness of the severely deformed material depends on the characteristics of its structural state. Grain refinement and changes in the density of dislocations have an ambiguous effect on the nanohardness of the alloys. The nanohardness variation is explained based on the current views on the mechanisms of the severe plastic deformation of alloys.

Strength properties and structure of a submicrocrystalline Al-Mg-Mn alloy under shock compression

The results of studying the strength of a submicrocrystalline aluminum A5083 alloy (chemical composition was 4.4Mg–0.6Mn–0.11Si–0.23Fe–0.03Cr–0.02Cu–0.06Ti wt % and Al base) under shockwave compression are presented. The submicrocrystalline structure of the alloy was produced in the process of dynamic channel-angular pressing at a strain rate of 104 s–1. The average size of crystallites in the alloy was 180–460 nm. Hugoniot elastic limit σHEL, dynamic yield stress σy, and the spall strength σSP of the submicrocrystalline alloy were determined based on the free-surface velocity profiles of samples during shock compression. It has been established that upon shock compression, the σHEL and σy of the submicrocrystalline alloy are higher than those of the coarse-grained alloy and σsp does not depend on the grain size. The maximum value of σHEL reached for the submicrocrystalline alloy is 0.66 GPa, which is greater than that in the coarse-crystalline alloy by 78%. The dynamic yield stress is σy = 0.31 GPa, which is higher than that of the coarse-crystalline alloy by 63%. The spall strength is σsp = 1.49 GPa. The evolution of the submicrocrystalline structure of the alloy during shock compression was studied. It has been established that a mixed nonequilibrium grain-subgrain structure with a fragment size of about 400 nm is retained after shock compression, and the dislocation density and the hardness of the alloy are increased.