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Increasing the strength of metallic alloys while maintaining formability is an interesting challenge for enabling new generations of lightweight structures and technologies. In this paper, we engineer aluminium alloys to contain a hierarchy of nanostructures and possess mechanical properties that expand known performance boundaries-an aerospace-grade 7075 alloy exhibits a yield strength and uniform elongation approaching 1 GPa and 5%, respectively. The nanostructural architecture was observed using novel high-resolution microscopy techniques and comprises a solid solution, free of precipitation, featuring (i) a high density of dislocations, (ii) subnanometre intragranular solute clusters, (iii) two geometries of nanometre-scale intergranular solute structures and (iv) grain sizes tens of nanometres in diameter. Our results demonstrate that this novel architecture offers a design pathway towards a new generation of super-strong materials with new regimes of property-performance space.

The influence of additional deformation heat treatments (DHTs), implemented by two regimes: (1) annealing and small additional deformation by high-pressure torsion (HPT) at room temperature (RT) and (2) HPT at elevated temperature to 10 turns and small additional HPT at RT, has been studied on the microstructure, mechanical properties and electrical conductivity of ultrafine-grained (UFG) Al-0.53Mg-0.27Zr (wt.%) alloy structured by HPT to 10 turns at RT. As is shown, both types of additional DHT lead to a substantial increase in plasticity (2–5 times) while maintaining high electrical conductivity (~53% IACS) and strength comprising 75–85% of the value in the pre-DHT state of the UFG alloy. The possible physical reasons for the revealed changes in the physical and mechanical properties are analyzed. Comparison of the strength and plasticity changes with the microstructure evolution after DHT of both types indicates that the increase in the density of introduced grain boundary dislocations is the most probable factor providing a tremendous increase in plasticity while maintaining a high level of strength in the UFG alloy under study. An outstanding combination of high strength (370 MPa), high elongation to failure (~15%) and significant electrical conductivity (~53% IACS) was achieved for the Al-Mg-Zr alloy. This combination of properties exceeds those obtained to date for this system, as well as for a number of other commercial conductor alloys based on the Al-Zr system. [ABSTRACT FROM AUTHOR]

This paper presents an overview of fundamentals and potential applications of ultrafine-grained Al-based conductors developed with the help of severe plastic deformation (SPD) techniques. Based on deliberate formation of nanoscale features (such as nanoprecipitates, segregation of solutes along crystallographic defects and so on) within ultrafine grains, it is possible to optimise their mechanical and functional performance enhancing the combination of strength and electrical conductivity to produce advanced lightweight conductors required by modern industries. Guidelines related to SPD-driven development of Al alloys with properties superior to those exhibited by traditionally processed conductors are discussed. [ABSTRACT FROM AUTHOR]

This paper features the changes in microstructure and properties of an Al–Fe alloy produced by casting with different solidification rates followed by severe plastic deformation and rolling. Particularly, different states of the as-cast Al–1.7 wt.% Fe alloy, obtained by conventional casting into a graphite mold (CC) and continuous casting into an electromagnetic mold (EMC), as well as after equal-channel angular pressing and subsequent cold rolling, were studied. Due to crystallization during casting into a graphite mold, particles of the Al6Fe phase are predominantly formed in the cast alloy, while casting into an electromagnetic mold leads to the formation of a mixture of particles, predominantly of the Al2Fe phase. The implementation of the two-stage processing by equal-channel angular pressing and cold rolling through the subsequent development of the ultrafine-grained structures ensured the achievement of the tensile strength and electrical conductivity of 257 MPa and 53.3% IACS in the CC alloy and 298 MPa and 51.3% IACS in the EMC alloy, respectively. Additional cold rolling led to a further reduction in grain size and refinement of particles in the second phase, making it possible to maintain a high level of strength after annealing at 230 °C for 1 h. The combination of high mechanical strength, electrical conductivity, and thermal stability can make these Al–Fe alloys a promising conductor material in addition to the commercial Al–Mg–Si and Al–Zr systems, depending on the evaluation of engineering cost and efficiency in industrial production. [ABSTRACT FROM AUTHOR]

Low temperature tensile and impression creep tests were carried out on an ultrafine-grained 7xxx series Al–4.8Zn–1.2 Mg–0.14Zr (wt%) alloy, which can be deformed for maximum elongation of about 200% at 150 °C. The characteristics of the deformation process, such as the strain rate sensitivity (SRS) and activation energy (Q) were determined by considering also the effect of threshold stress. Relatively high SRS of ∼ 0.35 and low activation energy of ∼ 92 kJ/mole were obtained, confirming the super ductility of the investigated ultrafine-grained alloy in the low temperature region between 140 and 160 °C. [ABSTRACT FROM AUTHOR]

The important benefits of ultrafine-grained (UFG) alloys for various applications stem from their enhanced superplastic properties. However, decreasing the temperature of superplasticity and providing superplastic forming at lower temperatures and higher strain rates is still a priority. Here, we disclose, for the first time, the mechanism by which grain boundary sliding and rotation are enhanced, when UFG materials have grain boundary segregation of specific alloying elements. Such an approach enables achieving superplasticity in commercial Al alloys at ultralow homologous temperatures below 0.5 (i.e. below 200°C), which is important for developing new efficient technologies for manufacturing complex-shaped metallic parts with enhanced service properties. For the first time, ultralow-temperature superplasticity is found in commercial 7xxx Al alloy. This discovery enables the development of new technologies for the superplastic forming of complex-shaped products with enhanced service properties. [ABSTRACT FROM AUTHOR]

Al-based immiscible systems, such as Al-RE (rare earth), seem to be promising materials for high conductivity conductors as RE alloying elements have zero solubility in Al and thus are less detrimental for electrical conductivity. The intermetallic phases, precipitated as small particles and uniformly distributed in the alloy's volume, may significantly increase the mechanical strength and thermal stability of alloy. However, the immiscible element compound concentration should be controlled as an excessive amount might result in a loss of electrical conductivity. Therefore, the optimization of RE concentration to obtain the best combination of mechanical strength and electrical conductivity is considered in this research. It focuses also on the effect of high-pressure torsion (HPT) and post deformation annealing temperature on mechanical and electrical properties of Al-RE (La + Ce) alloy. Alloys with total Ce and La concentrations of 2.5, 4.5 and 8.5 wt % are subjected to HPT at room temperature and subsequent annealing in the range of temperatures 230–400 °C. The optimal concentration of RE and processing parameters for enhancement of both mechanical strength and electrical conductivity are defined. [ABSTRACT FROM AUTHOR]

This paper investigates a dynamic aging effect induced by severe plastic deformation (SPD) and subsequent artificial aging on structure and mechanical properties of aluminum Al-Mg-Si alloys. Application of optimal processing parameters of SPD via equal-channel angular pressing with parallel channels and subsequent artificial aging ensures simultaneous enhancement of strength and ductility in the processed alloys. Ultrafine-grained microstructures with strengthening metastable β' and β'' precipitates generated during SPD processing and subsequent artificial aging provide enhanced strength due to significant grain boundary hardening and precipitation hardening. [ABSTRACT FROM AUTHOR]

Microstructural features and mechanical properties of an Al-Mg-Si alloy processed by high-pressure torsion (HPT) have been investigated using transmission electron microscopy, X-ray diffraction, three-dimensional atom probe, tensile tests and micro-hardness measurements. It is shown that HPT processing of the Al-Mg-Si alloy leads to a much stronger grain size refinement than of pure aluminium (down to 100 nm). Moreover, massive segregation of alloying elements along grain boundaries is observed. This nanostructure exhibits a yield stress even two times higher than that after a standard T6 heat treatment of the coarse-grained alloy. [ABSTRACT FROM AUTHOR]

This study focuses on the difference in microstructural features and physical properties of Al-2Fe and Al-4Fe alloys subjected to large plastic straining. The difference in the intermetallic particle morphology in the initial state is shown to be a key parameter influencing the particle and grain fragmentation process and, as a result, the properties of these two alloys. We demonstrate that the shape and average size of Al-Fe intermetallic particles provide stronger effect on the microstructure evolution during high pressure torsion (HPT) than their volume fraction. The formation of Fe supersaturated solid solution in Al in these two alloys during deformation is discussed in connection to the morphology of the intermetallic phase. The major microstructural attributes, responsible for the solid solution formation, are highlighted. [ABSTRACT FROM AUTHOR]

Herein, the characterization of microstructures and mechanical properties of Al–Zn alloys ultrafine‐grained (UFG) by using high pressure torsion (HPT) is surveyed. Emphasis is placed on the decomposition of the solid solution structures due to the HPT process, leading to unique mechanical and plastic properties of the UFG alloys. The decomposed microstructures, the grain boundaries wetted by Zn‐rich layers, as well as the softening, grain boundary sliding (GBS) with usually high strain rate sensitivity and super‐ductility of the HPT‐processed samples are described and discussed. Furthermore, the innovation potential of intensive GBS at room temperature is briefly considered. [ABSTRACT FROM AUTHOR]

Herein, the ultrafine‐grained (UFG) 7xxx series alloy Al–4.8Zn–1.2Mg–0.14Zr demonstrates superplasticity at unusually low temperatures of 120–170 °C while maintaining its high‐strength state. The UFG structure is formed by high pressure torsion (HPT) at room temperature (RT), which leads to a considerable increase in the strength characteristics by ≈60% compared with the material after conventional heat treatment T6. It is found that the UFG alloy exhibits thermostability when testing or annealing up to 170 °C. Deforming by tensile test at a strain rate of 10−4 s−1 and 10−3 s−1, the elongation to failure at 120 and 170 °C exceeds 250% and 500%, respectively, whereas the strain rate sensitivity reaches 0.45, which is a typical value characterizing superplastic deformation. After superplastic deformation, the UFG alloy maintains 25–50% higher strength characteristics at RT than that after conventional heat treatment T6. The origin of such superior behavior of the UFG alloy is discussed. [ABSTRACT FROM AUTHOR]

Superplastic deformation of polycrystalline materials is usually accommodated by diffusion-assisted grain boundary (GB) sliding at high temperatures. Lowering the temperature requirement for commercial superplastic forming enables green and cost-effective manufacturing. Recently, room-temperature (RT) superplasticity was realized in ultrafine-grained Al–Zn based alloys, but the underlying mechanism remains unclear. Here, we conducted in-situ tensile straining and post-mortem electron microscopy characterization, and atomistic density functional theory simulation to understand the RT superplasticity of an Al–15 Zn (at%) alloy. Results showed that the superplasticity is achieved by GB sliding and grain rotation, assisted by the continuous diffusion of Zn. In-situ observations showed Zn atoms diffusing from within grains to GBs, resulting in a Zn nanolayer at the GBs that acts as a solid lubricant to decrease the energy barrier of GB sliding. This research advances our understanding of diffusion-assisted deformation mechanism that is a prerequisite for the rational design of new materials with RT superplasticity. [Display omitted] [ABSTRACT FROM AUTHOR]

This research addresses fundamentals regarding the temperature-dependent composition of η phase in Al-Zn-Mg-Cu alloys under high pressure torsion (HPT) to uncover kinetics and thermodynamics governing the η phase composition evolution. Two-stage HPT experiments are deployed to study the stability of the high-temperature η under low-temperature processing. The first-stage HPT on a solid-solution-treated Al-Zn-Mg-Cu alloy (AA7075) at 200 ℃ for 10-revolutions is to get the high-temperature η, and the second-stage HPT is performed at either 100 ℃ or RT. Atom probe tomography reveals that the high-temperature η phase becomes chemically unstable during the low-temperature processing and its chemistry evolves towards low-temperature values. Surprisingly, a high-Mg Al-Mg phase is, for the first time, observed to form in the alloy under the 2nd-stage HPT processing, in correlation with the decomposition of the high-temperature η phase under the low-temperature processing. Unlike the 1st-stage HPT processed alloy, the 2nd-stage HPT processed alloy develops the segregation of Zn with other elements at grain boundary, accompanied with the chemical modification of the high-temperature η phase. The thermodynamics driving η phase composition variation with temperature provides the Al alloys with temperature variable for multi-stage treatments to engineer precipitation for optimised properties. [Display omitted] [ABSTRACT FROM AUTHOR]