Anisotropy in flow and microstructural evolution during superplastic deformation of a layered-microstructured AA8090 Al–Li alloy
25 May 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier)-Vol. 349, Iss: 1, pp 166-182
TL;DR: In this article, the superplastic forming grade sheets of AA8090 Al-Li alloy were observed to contain layers of different microstructure and microtexture across their cross-section along the normal to the rolling direction (RD).
Abstract: The superplastic forming grade sheets of AA8090 Al–Li alloy were observed to contain layers of different microstructure and microtexture across their cross-section along the normal to the rolling direction (RD). The surface layer (SL) material contained coarse equiaxed grains and the dominance of S {1 2 3}[6 3 4] texture whereas the center layer (CL) material contained fine elongated grains and the dominance of Bs {1 1 0}[1 1 2] texture. Tensile specimens, machined to represent the SL of 0.6 mm thickness from the surface towards center (SL), the CL of 0.6 mm thickness, obtained by removing the material of 0.6 mm thickness from each surface towards center (CL), and full thickness (FL) material of 1.8 mm thick, in a sheet of AA8090 Al–Li alloy, were deformed at optimum superplastic condition of strain rate=1×10 −3 s −1 and temperature=803 K to investigate the effect of loading direction. In SL material, the specimen parallel to RD exhibited maximum and the specimen perpendicular to RD exhibited minimum flow stresses. This trend was reversed in CL material. The anisotropy in flow stress could be explained on the basis of texture in the SL material, but the contribution of grain directionality became important in the CL material. The flow behavior of FL material was found to consist of the composite-like contributions of SL and CL materials.
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TL;DR: In this article, the effect of tensile deformation at 530°C at a constant strain rate of 5 × 10−4 −1 on the microstructure, texture and mechanical characteristics of the central layer of commercially processed superplastic Al-Li alloy (AA8090) sheet has been investigated.
Abstract: The effect of tensile deformation at 530 °C at a constant strain rate of 5 × 10−4 s−1 on the microstructure, texture and mechanical characteristics of the central layer of commercially processed superplastic Al–Li alloy (AA8090) sheet has been investigated. The strain rate sensitivity remained essentially constant during straining with m ∼ 0.53, despite a progressively changing microstructure. The initial sheet had a dominant cross-rolled “brass” texture centred on { 0 1 1 } 〈 1 1 2 〉 , which became weaker during deformation, but it was also possible to identify similar orientations which remained spatially aligned in the rolling direction for strains up to unity. The changes in microstructure and texture were not compatible with relative grain translation, i.e. grain boundary sliding. Modelling studies incorporating relative grain translation together with grain growth and orientation changes reinforced that conclusion, and lead to the view that rate sensitive slip is the primary deformation mechanism.
43 citations
TL;DR: In this article, the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy were analyzed using transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations.
Abstract: Precipitate redistribution and texture evolution are usually two concurrent aspects accompanying grain refinement induced by various surface treatment. However, the detailed precipitate redistribution characteristics and process, as well as crystallographic texture in the surface refined grain layer, are still far from full understanding. In this study, we focused on the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy. With the combination of transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations, a surface ultrafine grain (UFG) layer composed of both equiaxed and lamellar ultrafine grains and decorated by high density of coarse grain boundary precipitates (GBPs) were revealed. Further precession electron diffraction (PED) assisted orientation mapping unraveled that high angle grain boundaries rather than low angle grain boundaries are the most favorable nucleation sites for GBPs. The prominent precipitate redistribution can be divided into three successive and interrelated stages, i.e. the mechanically induced precipitate dissolution, solute diffusion and reprecipitation. The quantitative prediction based on pipe diffusion along dislocations and grain boundary diffusion proved the distribution feasibility of GBPs around UFGs. Based on PED and electron backscatter diffraction (EBSD) analyses, the crystallographic texture of the surface UFG layer was identified as a shear texture composed of major rotated cube texture {001} 〈110〉 and minor {111} 〈112〉, while that of the adjoining lamellar coarse grained matrix was pure brass. The SFT induced surface severe shear deformation is responsible for texture evolution.
28 citations
TL;DR: In this article, the mechanical properties and microstructures of the extruded 2196 Al-Cu-Li alloy plates under different heat treatment parameters are tested and characterized along different directions, and it is found that the mechanical property anisotropy of 2196 al-Li Alloy is significantly affected by heat treatment.
Abstract: The mechanical properties and microstructures of the extruded 2196 Al-Cu-Li alloy plates under different heat treatment parameters are tested and characterized along different directions. It is found that the mechanical property anisotropy of 2196 Al-Li alloy is significantly affected by heat treatment. The anisotropy is mainly caused by the differences of grain morphology, microtexture, recrystallization degree and secondary particles characteristics in different directions. The specimens in 0° and 90°directions have high strength, while the specimen in 45° direction has the best ductility. The main microtexture of alloy are {111} oriented A*1 and A*2 shear textures, and aging treatment has little effect on the grain morphology and microtexture. The decrease of mechanical property anisotropy after aging treatment is mainly due to the increase of number density and distribution uniformity of T1 phase. The elimination of PFZ and the increase of grain boundary strength are also conducive to the decrease of anisotropy. The dislocations introduced by pre-stretching is beneficial to the uniform precipitation of the fine phases, resulting in the optimal mechanical property homogeneity of the alloy. The ductility in different directions is also anisotropic, and the fracture mechanism changes from ductile to intergranular and cleavage fracture modes after heat treatment.
26 citations
TL;DR: In this article, the microstructural evolution of banded 5A90 Al-Li alloy during superplastic deformation at 475 °C with an initial strain rate of 8×10−4 s−1 was studied using EBSD technique.
Abstract: The microstructural evolution of banded 5A90 Al-Li alloy during superplastic deformation at 475 °C with an initial strain rate of 8×10−4 s−1 was studied using EBSD technique. The results showed that, before deformation, the grain shape appeared to be banded, the most grain boundaries belonged to low-angle boundaries, and the initial sheet had a dominate of {110}«112» brasstexture. During deformation, there were grain growth, grain shape change, misorientation increasing and textural weakening. The fraction of high-angle boundaries increased rapidly once the flow stress reached the peak value. Corresponding deformation mechanism for various stages of deformation was suggested. Dislocation activity was the dominant mechanism in the first stage, then dynamic recrystallization occurred, and grain rotation was expected as an accommodation for grain boundary sliding (GBS). At large strains, GBS was the main mechanism.
18 citations
23 Feb 2021-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the superplastic deformation behaviors and the evolution processes of the microstructures of an Al-Mg-Li alloy with initial banded grains were studied by means of SEM, EBSD, TEM and FIB techniques.
Abstract: The superplastic deformation behaviors and the evolution processes of the microstructures of an Al–Mg–Li alloy with initial banded grains were studied by means of SEM, EBSD, TEM and FIB techniques. Furthermore, the contribution of GBS and IDS of true strain from 0.21 to 0.74 was quantitatively calculated. The results showed that during the stretching process, the initial banded grains were transformed into equiaxed grains, accompanied by dynamic recrystallization. Dynamic recrystallization refined the grain size, increased the high-angle grain boundaries and reduced the texture. The true stress-strain curve showed work hardening and strain softening. At the initial stage of superplastic deformation, dislocations accumulated obviously, which counteracted the softening effect caused by dynamic recrystallization. Moreover, in this stage, the IDS was the dominant deformation mechanism, with a maximum contribution of 62.3%. In the strain softening stage, the change of m value showed that GBS was the dominant deformation mechanism, and DC and IDS were accommodation mechanisms.
18 citations
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