Microtexture, Grain Boundary and Grain Junction Evolution in Al-Li Sheet During Superplastic Forming

Abstract

The microtexture of superplastically deformed 8090 Al-Li sheet has been measured using electron backscatter diffraction, for true strains of 0, 0.25, 0.75, 1.5 and 2.4. The data has been interpreted in terms of individual texture variants, grain boundary types (low angle or high angle) and grain junction types (I-lines or U-lines, as defined by an extension to the O-lattice theory). A key feature of the results is that local textures tend to be dominated by only one or perhaps two orientation variants, which leads directly to the presence of a high proportion of low or medium angle boundaries and hence a high proportion of I-line grain junction types. These effects decrease with increasing superplastic strain. Since it has been previously suggested that the presence of I-lines indicates dislocation-related phenomena, and the presence of U-line grain junction types denotes diffusion-related phenomena, the proportion of each of these provides as indication of the predominant accommodation mechanism.