Crystallographic Texture and Yield Behavior of Al-Cu-Li (2195) Plate
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ABSTRACT Existing experimental texture analysis capabilities allow testing of theories on plasticity using polycrystal models. Aluminum-lithium alloys, which are particularly suited for aerospace applications due to excellent strength to weight ratio, typically possess pronounced texture. AlCu-Li (2195) thick plates were deformed by cold rolling to various thickness reductions. The plates exhibit a texture gradient through the plate thickness accompanied by a variation in yield strength values. The difference in yield strength values is related to the texture variation in terms of the texture components (ideal crystallographic orientations) identified from experimental measurements. A modified Taylor-based polycrystal plasticity model developed by Kocks and his colleagues is used to predict yield surfaces by incorporating texture data. Results of this investigation show that the texture intensities measured at certain ideal orientations increase or decrease with increasing deformation. These textural changes influence the value and anisotropy of the yield strength of the alloy. INTRODUCTION Studies of the various AI-Li alloys [1-3] conclude that the various particles that form during aging provide barriers to dislocation motion during slip. The major strengthening precipitate, T1 (Al2 CuLi), forms with artificial aging only on {111 } habit planes, preferentially at dislocation sites. This impedance provides these materials with improved strength properties over conventional aluminum alloys while their chemical compositions lead to lower densities than their conventional counterparts. For this reason, Al-Li alloys are of significant interest to the aerospace industries. Al-Li alloys are typically anisotropic and they exhibit strong textures. Anisotropy of mechanical properties in different directions of measurement is a concern in the forming of metals into shapes and parts. It is tied into considerations of the yield locus. Various factors cause anisotropy in metals, including elongated grains [4] and the presence of second-phase precipitates [1,5]. Researchers agree that crystallographic textures or preferred orientations resulting from thermomechanical treatment such as hot or cold rolling or stretching are most directly responsible for anisotropy in metal alloys [6]. For Al-Li alloys, crystallographic texture may also have an indirect effect on anisotropy resulting from the heterogeneous distribution of the primary strengthening precipitates on specific habit planes [7]. For these reasons, texture analysis is important for characterization of Al-Li materials. Textures are usually presented as pole figures or orientation distribution function (ODF) plots. However they may also be represented in terms of components, thus reducing the representation of the orientation distribution into a small set of specific orientations which describe a large number of crystallites present in the specimen [8]. This is useful for relating the presence of certain texture components to material behavior. In this paper, such discussi
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