Effects of grain shape and crystallographic texture on plastic anisotropy of aluminum alloy sheets

Plastic anisotropy of aluminum alloy sheets significantly affects the forming process and product performance. This dissertation addresses the quantitative effects of grain shape and crystallographic texture on plastic anisotropy of aluminum alloy sheets. The main goal is to extend Man's formula on q-value, which delineates the texture dependence of q-value, to one that considers also the influence of grain shape. Grain shape here is described by a second order tensor or a truncated expansion of the mean linear intercept function in spherical harmonics. Texture is represented by Roe's texture coefficients in the orientation distribution function. To examine the validity of the new formula and of Man's formulae on flow stress and q-value, uniaxial tensile tests were conducted to determine the angular dependence of flow stress and contraction ratio q in three batches of aluminum alloy samples. Texture coefficients were calculated from the pole figure data measured with X-ray diffraction. Orientation imaging microscopy and image processing analysis delivered the main experimental data on grain shape. The new formula, with texture coefficients truncated at l = 6, was shown to describe effectively the grain shape and texture dependence of the q-value that pertains to a commercial AA5754 CC aluminum O-temper material. Applying this formula to an AA5754 CC aluminum hot band and an AA3105 CC aluminum O-temper sample, however, suggested that for these materials the q-value was strongly influenced by some other microstructure (e.g., dislocations in the hot band). Moreover, this microstructural effect might have formally led to the same expression in the new formula because its influence on the q-value was also realized through a second order tensor similar to that which was used to describe grain shape.