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.
Citations
More filters
[...]
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.
31 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.
21 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.
14 citations
[...]
TL;DR: In this paper, the formation mechanism of the gradient particles was discussed and the results showed that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles of the SL is higher than that in the CL.
Abstract: Fine-grained 01420 Al-Li alloy sheets were produced by thermo-mechanical processing based on the mechanism of particle stimulated nucleation of recrystallization. The thermo-mechanically processed sheets were observed to contain layers of different microstructures along the thickness. The precipitate behavior of the second phase particles and their effects on the distribution of dislocations and layered recrystallized grain structure were analyzed by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffractometry(XRD). The formation mechanism of the gradient particles was discussed. The results show that after aging, a gradient distribution of large particles along the thickness is observed, the particles in the surface layer(SL) are distributed homogeneously, whereas those in the center layer(CL) are mainly distributed parallel to the rolling direction, and the volume fraction of the particles in the SL is higher than that in the CL. Subsequent rolling in the presence of layer-distributed particles results in a corresponding homogeneous distribution of highly strained regions in the SL and a banded distribution of them in CL, which is the main reason for the formation of layered grain structure along the thickness in the sheets.
12 citations
[...]
TL;DR: In this paper, a superplastic bulge forming of commercial grade AA8090 Al-Li alloy sheet was done, where three layers of distinct microstructural features along thickness direction were obtained from the as-received sheet.
Abstract: Superplastic bulge forming of commercial grade AA8090 Al–Li alloy sheet was done. The sheet contained three layers of distinct microstructural features along thickness direction. In order to understand the effect of such microstructure on the forming parameters, the blanks of three different layers, viz. surface layer, middle layer and composite layer, comprising of different microstructures, were obtained from the as-received sheet. Three different forming pressures—low, intermediate and high, corresponding to initial strain rates of 4 × 10 −4 , 1 × 10 −3 and 5 × 10 −3 s −1 , respectively, were employed for forming of each layer. The superplastic forming characteristics, including thickness and bulge profile, of surface layer were found to be superior to middle layer. It is interesting to find that the composite layer also exhibited better bulge profile and more uniform thickness distribution than middle layer. The difference in forming characteristics among different layers can be attributed to the presence of favorable equiaxed microstructure in the surface layer and unfavorable elongated grains in the middle layer.
10 citations
References
More filters
[...]
TL;DR: In this paper, a general relationship between stress and plastic strain in polycrystalline aggregate is derived for any metal in which individual crystals deform by slipping over preferred planes under a critical shear stress.
Abstract: Summary A general relationship between stress and plastic strain in a polycrystalline aggregate is derived for any metal in which individual crystals deform by slipping over preferred planes under a critical shear stress. Full account is taken of the non-uniform distortion due to mutual constraints between the grains of an aggregate. It is shown that a plastic potential exists which is identical with the yield function. Upper and lower bounds are obtained for an approximate calculation of this function for any applied system of combined stresses.
1,212 citations
[...]
TL;DR: In this paper, it was shown that the work-hardness of an isotropic aggregate of face-centred cubic crystals is a function only of the total plastic work if the grains hardened equally.
Abstract: Summary In continuation of a previous paper (Bishop and Hill 1951) it is conjectured that the work done in plastically deforming a polycrystal is approximately equal to that which would be done if the grains were free to deform equally. In conjunction with the principle of maximum plastic work, this enables the yield function of an aggregate to be calculated. This is done for an isotropic aggregate of face-centred cubic crystals, following a determination of the stresses needed to produce multi-slip. The theoretical yield criterion lies between those of Tresca and von Mises, in good agreement with observaton for copper and aluminum. It is shown further that the work-hardening of an aggregate would be a function only of the total plastic work if the grains hardened equally ; the departure from this functional relation is expressed explicitly in terms of the non-uniform hardening.
677 citations
Book•
[...]
01 Jan 1985
TL;DR: In this article, Wenk et al. describe the symmetry of pole figures and textures and their relationship to the texture of the textured surfaces of a porphyrias.
Abstract: L.E. Weiss and H.-R. Wenk, An Introduction. H.-R. Wenk, Measurement of Pole Figures. L.E. Weiss and H.-R. Wenk, Symmetry of Pole Figures and Textures. H.J. Bunge, Representation of Preferred Orientations. H.J. Bunge and C. Esling, The Harmonic Method. H. Schaeben, A. Vadon, and H.-R. Wenk, Vector Method. S. Matthies and H.-R. Wenk, ODF Reproduction with Conditional Ghost Correction. D.J. Barber, Dislocations and Microstructures. G. Gottstein and H. Mecking, Recrystallization. T.G. Langdon, Regimes of Plastic Deformation. P. Van Houtte and F. Wagner, Development of Textures by Slip and Twinning. G. Oertel, Reorientation due to Grain Shape. H. Mecking, Textures of Metals. J. Hirsch and K. L cke, Interpretation of the Copper*b1Brass Texture Transition by Quantitative ODF Analysis. H. Kern and A. Richter, Microstructures and Textures in Evaporites. H. Siemes and Ch. Hennig-Michaeli, Ore Minerals. H.-R. Wenk, Carbonates. G.P. Price, Preferred Orientations in Quartzites. J.-C.C. Mercier, Olivine and Pyroxenes. G. Oertel, Phyllosilicate Textures in Slates. J.L. Rosenfeld, Schistosity. B.E. Hobbs, The Geological Significance of Microfabric Analysis. H.C. Heard, Experimental Determination of Mechanical Properties. H.J. Bunge, Physical Properties of Polycrystals. P.R. Morris and J.W. Flowers, Texture and Magnetic Properties of Metals. H. Kern and H.-R. Wenk, Anisotropy in Rocks and the Geological Significance. References. Index.
588 citations
[...]
TL;DR: The importance attached to the development of aluminum-lithium based alloys may be deduced from the fact that over the past seven years four major international conferences (1-4) have been devoted to these materials: The first was held at Stone Mountain, Georgia, in 1980 (1), and the most recent was in Paris in 1987 (4) as discussed by the authors.
Abstract: The importance attached to the development of aluminum-lithium based alloys may be deduced from the fact that over the past seven years four major international conferences (1-4) have been devoted to these materials: The first was held at Stone Mountain, Georgia, in 1980 (1), and the most recent was in Paris in 1987 (4). This rapid sequence of conferences reflects intense research and devel opment activity within the laboratories of the aerospace companies, the aluminum companies, many universities, research institutes, and govern ment research establishments. One reason for this activity was the need for more fuel efficient aircraft because of escalating fuel prices during the 1970s: the addition of lithium to aluminum simultaneously reduces the density and increases the elastic modulus of the resultant alloy. A second and continuing impetus for the development of these materials comes from the requirements of military aircraft.
294 citations
[...]
TL;DR: In this paper, the subgrain growth kinetics of a high purity Al-0.05% Si single-phase aluminium alloy were investigated at room temperature and 350°C.
Abstract: Single crystals of orientation {110}〈001〉 of a high purity Al–0.05% Si single-phase aluminium alloy have been deformed in channel die plane strain compression at room temperature and 350°C. The specimens were annealed at temperatures between 250 and 400°C and detailed measurements have been made of the extensive subgrain growth which occurs in these crystals. It was found that subgrain growth tended to be discontinuous, confirming earlier experimental and theoretical work, and showing that subgrain growth is quite different from normal grain growth. The mean misorientation between subgrains decreased during annealing and this was shown to have a strong effect on the kinetics of subgrain growth. The mobilities of low angle boundaries (2.6°<θ<5.6°) at temperatures between 250 and 400°C were determined from the subgrain growth kinetics and the activation energies for migration found to be consistent with control by lattice diffusion of solute. The boundary mobilities were found to increase rapidly with increasing misorientation and the results have been compared with the predictions of current theories.
170 citations