Crystal-plasticity simulation of the correlation of microtexture and roping in AA 6xxx Al-Mg-Si sheet alloys for automotive applications

The occurrence of roping in Al-alloy sheet for car body applications is caused by the collective deformation of band-like clusters of grains with similar crystallographic orientation. Large-scale orientation maps obtained by electron backscattered diffraction (EBSD) are input into a visco-plastic, self-consistent, crystal-plasticity model to analyse the strain anisotropy caused by the spatial distribution of the recrystallization texture components and, in turn, its correlation with roping. Two versions of the crystal-plasticity roping model are devised and tested against two AA 6016 sheets distinguished by different levels of roping. (i) EBSD orientation maps are acquired at low magnification in the standard sheet plane. The roping tendency is derived from the local dispersion in through-thickness strain rate for the full EBSD map by means of a single-crystal plasticity version of the model. This enables study of the influence of orientation topography on surface appearance and assessment of the impact of the recrystallization texture orientations on roping. (ii) A second set of measurements are carried out in the short transverse section of the sheets to get information on the distribution and morphology of orientation clusters through the sheet thickness. Here, a consecutive series of narrow bands in the EBSD maps are considered, and the variation in macroscopic strain response from band to band is determined with a polycrystal-plasticity model. For a given deformation of the sample, these simulations yield quantitative information on the level of roping of Al-alloy sheet for car body applications. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.