A.D. Kotov

Effect of the solid-solution composition on the superplasticity characteristics of Al-Zn-Mg-Cu-Ni-Zr Alloys

The structure and superplasticity characteristics of the Al-Zn-Mg-Cu-Ni-Zr alloys with different amounts of Zn and Mg have been analyzed. It has been demonstrated that for the formation of a micrograined structure and superplasticity effects, a bimodal size distribution of particles is required, i.e., the presence of coarse eutectic particles of Al3Ni and dispersed Al3Zr particles, and also the presence of highly alloyed solid solution is obligatory. In the case of a low-alloy solid solution in the alloys of this system, the recrystallization is hampered, both at heating and at the initial stage of the alloy deformation. An increase in the amount of Zn and Mg in the aluminum solid solution stimulates the formation of finer grains, a decrease in the yield stress, an increase in the strain-rate sensitivity m, and a growth in the values of relative elongation.

Development of mathematical models of superplasticity properties as a function of parameters of aluminum alloys of Al-Mg-Si system

The article discusses the superplasticity properties and structure parameters of cold-worked alloys of a quasi-binary section of the Al-Mg-Si system with a volume fraction of eutectic particles of 0.08–0.18. Mathematical models of yield stress and effective elongation as a function of the structure and engineering parameters have been developed for alloys of this system. An analysis of the developed models shows that, in the temperature range of 520–560°C, superplastic deformation is controlled by the rate of diffusion of aluminum atoms in the grain bulk.

Effect of adding chromium on internal friction and superplasticity of alloys of the Al – Mg system

Differences are revealed in the microstructure, superplasticity, and internal friction properties of superplastic specimens of alloys Al – 4.9% Mg – 0.6% Mn and Al – 4.9% Mg – 0.6% Mn – 0.25% Cr. The dynamics of structural changes during alloy superplastic deformation are studied. Effects connected with recrystallization and grain-boundary relaxation on internal friction temperature dependences are identified.

High-strain-rate superplasticity of the Al–Zn–Mg–Cu alloys with Fe and Ni additions

During high-strain-rate superplastic deformation, superplasticity indices, and the microstructure of two Al–Zn–Mg–Cu–Zr alloys with additions of nickel and iron, which contain equal volume fractions of eutectic particles of Al3Ni or Al9FeNi, have been compared. It has been shown that the alloys exhibit superplasticity with 300–800% elongations at the strain rates of 1 × 10–2–1 × 10–1 s–1. The differences in the kinetics of alloy recrystallization in the course of heating and deformation at different temperatures and rates of the superplastic deformation, which are related to the various parameters of the particles of the eutectic phases, have been found. At strain rates higher than 4 × 10–2, in the alloy with Fe and Ni, a partially nonrecrystallized structure is retained up to material failure and, in the alloy with Ni, a completely recrystallized structure is formed at rates of up to 1 × 10–1 s–1.

Effect of Alloying on Superplasticity of Two-Phase Brasses

Superplasticity characteristics of two-component and multicomponent brasses in the temperature range 525–600°C have been investigated at tension tests under the conditions of stepwise enhancement in the strain rate and when maintaining a constant strain rate of 1 × 10–3 s–1. The effective energy for activating superplastic deformation has been determined. It has been shown that brass alloyed with aluminum, tin, and iron exhibits large elongations and less porosity due to superplastic deformation. Changes in the granular structure and sample surfaces have been analyzed after deformation, and signs of grain-boundary sliding and intragrain deformation have been revealed in the alloys studied.

Analysis of softening alloys of the Al-Ni system containing particles of variable dispersity

Regularities of the deformation strengthening and softening of aluminum alloys containing second-phase Al3Ni particles 0.3 to 2.2 μm in size with a volume fraction from 0.03 to 0.1 are investigated during cold deformation and subsequent annealing at 0.6tm. It is shown that the largest hardness increment is observed for alloys with a maximal fraction of fine particles (d = 0.3 μm) after rolling deformation larger than 0.4. Fine particles prevent the development of crystallization upon true deformation up to 2.3, thereby effectively inhibiting softening. An increase in the particle size to 1.2–2.2 μm stimulates nucleation during recrystallization, substantially accelerating this process. For example, in order to ensure recrystallization uniformly over the entire sheet volume at d = 2.2 μm, cold deformation with ɛ = 0.4 is sufficient.

Formation of micrograin structure and superplastic state in alloys of the Al–Cu–Mg–Fe–Ni system

The methods of light and scanning electron microscopy and x-ray phase and thermal analysis are used to study the effect of the special features of the production process on the characteristics of the grain structure and super-elasticity of sheets from alloys based on the Al – Cu – Mg – Fe – Ni system. It is shown that the use of annealing in saltpeter before the superplastic deformation improves the superplasticity parameters of the alloys.

Fine-Grained Structure and Superplasticity of Al – Cu – Mg – Fe - Ni Alloys

The microstructure of Al – Cu – Mg – Fe – Ni alloys with Mn and Zr additions was analyzed by optical and scanning electron microscopy, internal friction, X-ray and calorimetric analysis in order to optimize technology of superplastic alloy preparation. It is shown that the S (Al2CuMg) phase precipitates during hot rolling and dissolves during annealing. This allows to create fine-grained recrystallized structure and to achieve elongation of 320 % at the strain rate of 1×10-3 s-1 during superplasticity testing. It is shown that annealing in saltpeter before superplastic deformation improves the superplastic behavior: at the constant strain rate of 4×10-3 s-1 elongation is 500 %.

Influence of Al3Ni crystallisation origin particles on hot deformation behaviour of aluminium based alloys

Abstract Binary Al–Ni, Al–Mg and ternary Al–Mg–Ni alloys containing various dispersions and volume fraction of second-phase particles of crystallisation origin were compressed in a temperature range of 200–500 °C and at strain rates of 0.1, 1, 10, 30 s−1 using the Gleeble 3800 thermomechanical simulator. Verification of axisymmetric compression tests was made by finite-element modelling. Constitutive models of hot deformation were constructed and effective activation energy of hot deformation was determined. It was found that the flow stress is lowered by decreasing the Al3Ni particle size in case of a low 0.03 volume fraction of particles in binary Al–Ni alloys. Intensive softening at large strains was achieved in the alloy with a 0.1 volume fraction of fine Al3Ni particles. Microstructure investigations confirmed that softening is a result of the dynamic restoration processes which were accelerated by fine particles. In contrast, the size of the particles had no influence on the flow stress of ternary Al–Mg–Ni alloy due to significant work hardening of the aluminium solid solution. Atoms of Mg in the aluminium solid solution significantly affect the deformation process and lead to the growth of the effective activation energy from 130–150 kJ/mol in the binary Al–Ni alloys to 170–190 kJ/mol in the ternary Al–Mg–Ni alloy.

Formation of Fine-Grained Structure and Superplasticity in Commercial Aluminum Alloy 1565ch

A process for fabricating 5-mm-thick sheets from alloy 1565ch with recrystallized grains less than 10 μm in size is developed, which involves superplastic forming and provides elevated mechanical properties at room temperature. The parameters of superplasticity and the mechanical properties of alloy 1565ch are determined. Test forming of a dome-shape model part is performed.