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Abstract: Defects and deformation structures including 0° and 60° full dislocations, 30° Shockley partials, stacking faults and deformation twins in a nanostructured Al–Mg alloy processed by high-pressure torsion were identified using high-resolution transmission electron microscopy. The twinning mechanism previously predicted by the molecular dynamics simulation, i.e., the homogeneous mechanism involving dynamic overlapping of the stacking faults inside grains, was directly verified. A four-layer twin formed by the dynamic overlapping of four stacking faults was experimentally observed. Deformation twins and stacking faults formed by partial dislocations in ultrafine grains were experimentally confirmed. These results suggest that partial dislocation emissions from grain boundaries could become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. [Copyright &y& Elsevier]

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]

Bulk nanostructured (NS) metallic materials usually have high strength but extremely low ductility. In this study, we successfully prepared a bulk NS binary Al–7 Mg alloy possessing both high strength and high uniform ductility, approaching ∼600 MPa and ∼14%, respectively, by utilizing room temperature equal channel angular pressing (ECAP) combined with inter-pass annealing. The mechanism that governs the high ductility in the alloy and especially the role of the high Mg solute concentration was explored in terms of microstructure analysis. [ABSTRACT FROM AUTHOR]

Achieving high strength and uniform deformation simultaneously in Al alloys processed by severe plastic deformation (SPD) remains a challenging task as these alloys usually possess high strength but very limited uniform deformability, i.e.<∼4%. In the present work, however, high strength (∼507 MPa) and large uniform elongation (∼11%) were achieved simultaneously in a binary Al alloy by using room-temperature equal-channel angular pressing (ECAP) and a high solute Mg content. Detailed characterization by electron backscattered diffraction (EBSD), conventional transmission electron microscopy (TEM) and delicate ASTAR-TEM orientation imaging has been carried out to reveal the microstructure evolution. It was found that it was difficult to form well-developed substructures in Al–7 Mg deformed by 1 pass or 2 passes of ECAP, in contrast to the pure Al and dilute Al–Mg alloys deformed under similar conditions, where well-aligned subgrains and cells are frequently formed. As a result, a bimodal grain structure, i.e. ultrafine/fine grains with mean sizes of < ∼500 nm were developed accompanied by micron-sized grains having a high dislocation density after 3 passes. The high strength is due to a combination of strengthening by the high density of dislocations, ultrafine grains and high solute Mg content. The high uniform elongation is due primarily to the enhanced work hardening resulted from the high solute Mg content and the bimodal grain structure, while the dynamic strain aging effect is supposed also to contribute to the high ductility. Most importantly, the present work revealed that inhomogeneous deformation during SPD introduced by high solid-solution contents can be utilized as a strategy to generate desirable bimodal grain structure, gaining both a high strength and high uniform ductility. [ABSTRACT FROM AUTHOR]

Abstract: Metallic materials processed by severe plastic deformation generally possess very high strength but a rather low uniform elongation, usually <5%. In the present Al–7Mg alloy processed by room temperature equal channel angular pressing combined with inter-pass annealing, impressive combination of high ductility (elongation~14.5%) and high strength (UTS~600MPa) was achieved. The high ductility was rationalized by an enhanced work hardening originated from the pronounced dynamic strain aging effect and a bimodal grain structure. The high strength was mainly due to a prominent grain refinement and high dislocation density. [Copyright &y& Elsevier]

Abstract: The annealing response in a binary Al–7Mg alloy processed at room temperature by equal channel angular pressing (ECAP) has been investigated via X-ray diffraction (XRD), electron-probe micro analysis (EPMA) and electron backscattering diffraction (EBSD). After ECAP and subsequent annealing, Mg remains mainly homogeneously distributed in solid solution. A bimodal structure with ultrafine grains accompanied by micrometer-sized crystallites was developed after 3 passes. Upon annealing at ~275°C for 96h, extensive recovery was observed in the as-deformed material, leading to a relatively uniform microstructure; at ~300°C a discontinuous recrystallization initiated in less than 30s with subsequent grain growth clearly evident. Such remarkable thermal stability, i.e., slower recovery and recrystallization kinetics, of the present material, in contrast to other severely deformed commercial pure Al and Al–Mg alloys, is due mainly to the presence of high Mg solid solution contents, the formation of the bimodal structure consisting of both coarse crystallites and ultrafine grains. In addition, the possible Mg-containing precipitates during annealing might also retard the recrystallization kinetics. [Copyright &y& Elsevier]