| Yield strength has been measured in multiple orientations for several regions in each of three aluminum alloy extrusions which contain distinct textures and microstructures. In some cases, the experimental yield anisotropy does not correspond to the Taylor factor variation predicted by the specimen texture. This indicates that slip system orientation is not the only factor influencing the plastic anisotropy. The two primary objectives of this research were to isolate and identify any additional causes of yield strength anisotropy, and to develop a quantitative model that incorporates the anisotropic strengthening effect of these other factors. An anisotropic strengthening contribution due to plate-shaped precipitates was determined to be the principal cause of the inability of the Taylor factor to adequately describe the yield anisotropy.; Yield strength models incorporating matrix and precipitate effects were developed for plastically-deforming and elastical-deforming precipitates. In all tested regions, these models predicted the experimental yield strength variation more accurately than the Taylor factor model. Generally, precipitates on (100) habit planes, {dollar}thetaspprime{dollar}, are predicted to minimize the anisotropy due to texture; precipitates on (111) habit planes, T{dollar}sb1{dollar}, are predicted to accentuate the anisotropy due to texture; and spherical precipitates, {dollar}deltaspprime{dollar}, are predicted to mimic the anisotropy due to texture.; A series of yield strength measurements for several heat treatments was performed to observe the increased effect of precipitates on the yield anisotropy. As the volume fraction of T{dollar}sb1{dollar} precipitates increased with increased aging time, the magnitude of the experimental yield anisotropy increased in agreement with model predictions. Yield strength measurements from previously untested out-of-plane orientations were performed to fully characterize the deformation behavior of the extrusions. |
