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 paper, the Zn-1.1% Al alloy with a strong rolling texture has been tested under the conditions of superplasticity, and the samples were cut from a sheet 5 mm thick at an angle of 20° with the sheet plane.
Abstract: The Zn-1.1% Al alloy with a strong rolling texture has been tested under the conditions of superplasticity. The samples were cut from a sheet 5 mm thick at an angle of 20° with the sheet plane. The material in the initial state was characterized by the absence of a texture gradient over the sample thickness. Deformation led to a substantial weakening of texture maxima inside the sheet and their retention at the surface. Estimate of intragrain slip revealed that the contribution from slip was greater in deeper layers and smaller at the sheet surface. The effect was explained by different conditions of accommodation of grain-boundary sliding at the surface and inside the sheet.
TL;DR: In this paper , the effect of preliminary 3% tension and artificial ageing regimes on the structure and properties of Al-Li alloy 2A93-T3 sheet is studied, and EBSD analysis of the alloy are conducted.
Abstract: The effect of preliminary 3% tension and artificial ageing regimes on the structure and properties of Al – Li alloy 2A93-T3 sheet is studied. Tensile tests and EBSD analysis of the alloy are conducted. Fracture surfaces are analyzed, and chemical element distribution within the structure is determined. It is established that preliminary tension facilitates failure of coarse T2 and R phases within the structure and formation of fine hardening -phase, a large number of low-angle boundaries and a new S-texture, which increase alloy strength after ageing. Amore effective two-stage artificial ageing regime is proposed.
01 May 2023-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper , the microstructure evolution and superplastic deformation mechanisms of a 2A97 Al-Cu-Li alloy with initial banded grains were studied by using electron backscatter diffraction and focused ion beam techniques.
Abstract: The microstructure evolution and superplastic deformation mechanisms of a 2A97 Al–Cu–Li alloy (Al-3.4Cu-1.5Li-0.5Zn-0.4Mg-0.3Mn-0.15Zr) with initial banded grains were studied by using electron backscatter diffraction and focused ion beam techniques. The uniaxial superplastic tensile tests were carried out at a temperature of 430 °C and an initial strain rate of 2 × 10−3 s−1. The surface studies under a large true strain range (0–1.61) were achieved to investigate the superplastic deformation mechanisms. The results showed that the banded grains transformed into equiaxed grains due to dynamic recrystallization during deformation, accompanied by texture spreading, misorientation distribution randomization, and dislocation density reduction. The superplastic deformation process can be divided into two stages according to the microstructure characteristics and deformation mechanisms. In the primary deformation stage, the alloy was mainly composed of banded-grained structures, the intragranular dislocation slip (IDS) dominated the deformation and accounted for 54.1% contribution to the total deformation. When the true strain raised to 1.1, the deformation entered the second stage where the equiaxed grains became dominant, the grain boundary sliding became the main deformation mechanism and accounted for 54.4% contribution to the total deformation. A modified Ashby−Verrall model accompanied by IDS is suggested, which plays a crucial role in the superplastic deformation of the studied alloy.
TL;DR: In this paper, in situ tensile tests of extruded 1420 Al-Li alloy were investigated in field emission scanning electron microscope, and the fracture process is as follows: in the initial stage of tension, the dislocation begins to move, and pile up when meeting strengthening phases; the dislocations cuts through the strengthening phases, and induces their break; the subsequent dislocation moves through the broken strengthening phases leading to the initiating and propagating fast of the cracks; with opening of small cracks produced at multiple sites, the longer cracks form and keep the propagating, at last
Abstract: In-situ tensile tests of extruded 1420 Al-Li alloy were investigated in field emission scanning electron microscope. Results show that the fracture process is as follows: in the initial stage of tension, the dislocation begins to move, and pile up when meeting strengthening phases; the dislocation cuts through the strengthening phases, and induces their break; the subsequent dislocation moves through the broken strengthening phases, leading to the initiating and propagating fast of the cracks; with opening of small cracks produced at multiple sites, the longer cracks form and keep the propagating, at last the main crack form, result in the fracture of the sample. The fracture mode of extruded 1420 alloy is mixture of ductile and transgranular fracture. The weak texture of extruded 1420 sample transformed from texture {001} to {018} similar to texture {001} of cubic system after tension fracture
References
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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.
1,251 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.
702 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.
598 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.
188 citations