The structure and mechanical properties of composites consisting of a metal matrix based on aluminum and its alloys of different compositions (AA-3003 and AA-5154) and graphene synthes sized in situ under a layer of molten salts were investigated depending on the chemical composition and grain size of the matrix. Aluminum matrix composites of three compositions were studied in as-cast coarse-grained, deformed fine-grained (grain size < 1 mm), and deformed sub microcrystalline (grain size < 1 μm) states in order to compare the structural characteristics of composites with different grain sizes. The composites were subjected to deformation with a split Hopkinson (Kolsky) bar and to dynamic-channel angular pressing. The hardness and dynamic mechanical properties of the composites were measured at strain rates $\dot{\epsilon }$ from 1.8 − 4.7 × 10³ to 1.6 − 2.4 × 10⁵ s⁻¹. It was found that grain refinement induced a sharp increase in the hardness of composites with various compositions (by a factor of 1.6–2.6). A correlation of the elastic-plastic properties of the aluminum matrix composites with the grain sizes and chemical compositions of the matrices was established. A transition from coarse-grained to sub microcrystalline structure was shown to improve the elastic-plastic properties on average by a factor of 1.5. It was proved that the reinforcing effect of graphene increased with the decreasing grain size of the matrix. Mechanisms of reinforcement of the aluminum matrix composites using graphene were proposed.

A number of regularities of phase and structural transitions in an economically iron and nickel doped aluminum alloy with eutectic-forming elements (nikalin) at high shear strains under...

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...

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 σ_HEL, dynamic yield stress σ_y, and the spall strength σ_SP 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 σ_HEL and σ_y of the submicrocrystalline alloy are higher than those of the coarse-grained alloy and σ_sp does not depend on the grain size. The maximum value of σ_HEL 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 σ_y = 0.31 GPa, which is higher than that of the coarse-crystalline alloy by 63%. The spall strength is σ_sp = 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.

This paper identifies the mechanisms of phase and structural transformations during severe plastic deformation by shearing under pressure (high-pressure torsion) of an Al-Zn-Mg-Fe-Ni-based aluminum alloy depending on different initial states of the material (an ingot after homogenizing annealing and a rod produced by radial-shear rolling). Scanning and transmission electron microscopy are used to determine the morphological and size characteristics of the structural constituents of the alloy after high-pressure torsion. It has been found that, irrespective of the history under high-pressure torsion, fragmentation and dynamic recrystallization results in a nanostructural alloy with a high microhardness of 2000 to 2600 MPa. Combined deformation processing (high-pressure torsion + radial-shear rolling) is shown to yield a nanocomposite reinforced with dispersed intermetallic phases of different origins, namely Al₉FeNi eutectic aluminides and MgZn₂, Al₂Mg₃Zn₃, and Al₃Zr secondary phases. The results of uniaxial tensile testing demonstrate good mechanical properties of the composite (ultimate tensile strength of 640 MPa, tensile yield strength of 628 MPa, and elongation of 5%).

Experimental evidence of deformation twinning in coarse-grained aluminium is presented for the first time using electron backscatter diffraction technique. This phenomenon occurs when using a novel method of severe plastic deformation referred to as dynamic channel angular pressing. A pressing die had two channels of equal cross-section intersecting at an angle of 90°. Special gun accelerated the sample up to the rate of 100 m s^(-1) and directed it into the die. As a result, the strain rate was about 10^5 s^(-1). Twin-oriented mesobands of 3 to 20 μm in width appear predominantly near grain boundaries after deformation. Crystallographic peculiarities of the mesobands formed in two different grains were examined in detail. Analysis of a deviation of their misorientations from the ideal twin misorientation showed that the first mesoband family could be formed at an early stage of the first pass of the dynamic channel angular pressing, while the second family – at a later stage. The mesobands were suggested to form by successive nucleation and coalescence of microscopic twins during the shear localization. Results have shown that, deformation twinning occurs in aluminum, which is characterized by higher stacking fault energy and higher dislocation mobility, only under high strain-rate dynamic deformation.