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Mechanical properties at 77 K and 295 K and surface characteristics of an AA6060 alloy have been studied. The alloy exhibited significant differences in mechanical properties and fracture mechanisms at 77 K in comparison with that at 295 K. When the temperature decreases, the yield strength, the ultimate tensile strength and ductility to fracture are drastically increased from 217.2 MPa, 252.4 MPa, 14.5% to 251.6 MPa, 335.9 Mpa, 21.5% respectively, and the average diameter of dimples decreases from ~8 µm to ~3 µm. It is proposed that the changed behavior at cryogenic temperature can be attributed to an increased accumulation of dislocations at low temperature. Detailed inspections of the deformed polished sample surfaces show that slip localization in wide slip-bands is not promoted at 77 K, indicating that crystallographic slip is homogeneous, while activation of surface slip systems forming wide slip bands is much easier at 295 K and therefore the surfaces were deformed more in-homogeneously and localized. The homogeneity in slip behavior introduced more topography at 77 K than observed at 295 K and the enhanced topography might be due to more 3-dimensional (3D) lattice rotation in grains having a high Schmid factor, hence introducing more accumulation of local displacements in the thickness direction. [ABSTRACT FROM AUTHOR]

The PLC band parameters are studied in an AA2219 aluminium alloy using a newly developed laser speckle technique for the direct observation of PLC bands. It is observed that though the magnitude of serration is larger in the solution treated condition, the PLC bands are brighter and sharper in the as-received condition. The band multiplicity is much greater, and band width and band velocity are much lower in the as-received condition as compared to the solution-treated condition. Band angle is not affected by the specimen condition. The specimen orientation, on the other hand, does not make much difference in the mechanical properties, serration characteristics and PLC band parameters of the AA2219 alloy tested in the solution-treated condition. The serration characteristics and PLC band behaviour are also found to be similar in the AA5082, AA7020 and AA2219 alloys tested in the solution-treated condition. These various effects are explained by solute content and microstructure of the material. [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]

Peak-aged AA6082 flat extrusions were cryorolled at liquid nitrogen temperature to three different thickness reductions, the reductions were 21%, 42% and 85%, respectively. Microstructure and plastic deformation behaviors of the initial as well as the rolled materials were studied by means of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests at room temperature. The initial material showed fibrous grain structure. After cryorolling to 21% thickness reduction, grains in the alloy were obviously elongated and importantly, microband traces were detected in selected grains. More detailed information was obtained in the alloy after 42% thickness reduction. Here, numerous microbands aligned along slip planes with the highest resolved shear stress, producing fragmentation of grains, while rests of elongated grains were microband-free. A cryorolling strain of 85% has been found to be desirable for producing a hierarchical microstructure in the materials volume, featuring nano- and ultrafine grains with size <100 nm coexisted with micro-sized grains. The development of hierarchical microstructure could be considered as a consequence of the intersection between families of microbands. As a result, both the strength and uniform elongation of the severely cryorolled alloy, i.e. 85% thickness reduction, were more superior to other rolled alloys. Therefore, this study revealed that the single processing procedure, i.e., cryorolling, can be utilized to tailor for desired properties in favor of both strength and ductility for peak-aged AA6082 extrusions. [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 evolution of microstructure and texture of an extruded GW102K Mg alloy processed by cyclic extrusion and compression (CEC) at 450°C were investigated. Tensile tests were performed at room temperature and strain rate 5×10−3 s−1. The results show that the microstructure was effectively refined, and the initial fiber texture became disintegrated and developed a new texture after 14 CEC passes. It was found that the strength and ductility were simultaneously increased compared with the as-extruded alloy. In particular, the elongation and yield strength were related in a line relationship having a positive slope. As the texture changed and texture intensity decreased, substantial grain refinement was observed. The hard second-phase particles were considered to be responsible for the uncommon properties of the GW102K alloy processed by CEC. [Copyright &y& Elsevier]