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Image, graphical abstract The aluminum-zirconium (Al-Zr) alloys are of interest because of their superior thermal stability and good electrical conuctivity, but their main drawback is their rather low hardness (<75 Hv) even after severe plastic deformation (SPD). These alloys, which are actually composites of Al and Al 3 Zr intermetallics (D0 23 tetragonal structure), do not show age-hardening behavior due to the immiscibility of Zr in Al. In this study, ultra-SPD with shear strains up to 40,000, realized by high-pressure torsion (HPT), is employed to generate supersaturated solid solution in an Al-Zr alloy. Subsequent aging leads to unusual precipitation of AlZr precipitates at grain boundaries (Bf orthorhombic structure) and of coherent metastable Al 3 Zr precipitates within grain interiors (L1 2 cubic structure). It is found that the supersaturation of Zr in Al by ultra-SPD is controlled by an ultrafast dynamic diffusion which is comparable to surface diffusion, while the formation of precipitates by static aging is controlled by lattice and pipe diffusions. These microstructural features provide exceptional increase in hardness up to 148 Hv, great thermal stability up to 523 K and reasonable electrical conductivity up to 35 %IACS. Detailed analysis shows that ~30% of this hardening is caused by precipitation strengthening, while extra hardening is achieved due to nanograin formation, grain-boundary segregation and dislocation accumulation. This study introduces a rational approach to produce novel age-hardenable Al alloys with high thermal stability and reasonable electrical conductivity by application of ultra-SPD. [ABSTRACT FROM AUTHOR]

Abstract Al-Mg alloys are a series of low cost and low density Al alloys, which show remarkable strengthening during deformation. In this work, study of commercial purity Al, Al-0.5Mg and Al-4.1Mg alloys was carried out to investigate the effect of Mg on materials strengthening. Slight solid solution strengthening by Mg addition is found in the as-cast alloys. While further significant strengthening effect is achieved in the alloys produced by high pressure torsion. An extraordinarily high strength of ~800 MPa is achieved in the Al-4.1Mg alloy, as a result of deformation induced ultrafine grains, high density stacking faults and Mg segregation. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Combining transmission Kikuchi diffraction, high resolution transmission electron microscopy and atom probe tomography, we investigated an Al-Zn-Mg-Cu alloy (AA7075) processed by high-pressure torsion (HPT) at room temperature and 200 °C, with an objective to reveal the deformation-induced precipitation and segregation of elements at grain boundaries, and to study their appearance at different processing regimes. Although HPT processing at the two temperatures both induced the formation of ŋ phase, ŋ precipitates formed at the two temperatures have different chemical compositions. The increase of the HPT processing temperature increased significantly segregation of Mg and Cu at grain boundaries. The HPT–induced segregation and decomposition of the alloy have a significant effect on its mechanical strength. Our results open a way for achieving advanced mechanical properties in nanostructured metals and alloys by designing their precipitation and segregation through the control of SPD processing regimes. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Exploring the redistribution mechanism of Mg from the perspective of experimental observation has been a long-term yet challenging attempt in Al-Mg alloys. Here we demonstrate a simple but effective approach to obtain non-uniform Mg solute distribution (i.e., Mg-enriched/depletion zones) around typical grain boundaries (GBs) in a nanocrystalline Al-8 Mg alloy. This abnormal segregation was detected by both high-angle annular dark-field scanning transmission electron microscopy and atom probe tomography. The results show that local strain and GB migration during deformation leads to spatially inhomogeneous Mg solute distribution around the GBs. Both the non-uniform distribution and the broadened GBs can hinder GB migration and dislocation motion, thus enhance the strength. An inhomogeneous solute distribution mechanism of Mg atoms is proposed based on the extensive investigations. This study may help with developing new strengthening mechanisms of nanocrystalline materials. [Display omitted] • Atomic-scale non-uniform Mg solute distribution near typical GBs successfully explored in a nanocrystalline Al-8 Mg alloy. • Both local strain and GB migration lead to spatially inhomogeneous Mg solute distribution around the GBs. • The non-uniform Mg solute distribution (i.e., Mg-enriched/depletion zones) expands the width of GBs. • Both the non-uniform distribution and the broadened GBs hinder GB migration and dislocation motion thus enhance the strength. • A new inhomogeneous solute distribution mechanism of Mg around the GBs proposed. [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]