EFFECT OF TEXTURE AND MICROSTRUCTURE ON PLASTIC ANISOTROPY OF ALUMINUM SHEET

摘要

Man recently derived formulae which delineate the effects of crystallographic texture on flow stress anisotropy and on the angular dependence of the q-value in orthorhombic sheets of cubic metals. In these formulae, q and the uniaxial flow stress sigma are given as linear combinations of explicit expressions of the texture coefficients and the angle theta that the tensile axis makes with the rolling direction of the sheet, whereas the coefficients sigma_(iso), a_i, and b_i (i = 1,2) of the linear combinations are material parameters which depend on microstructures other than texture. In a previous study Man's formulae were corroborated by experimental data on an AA5xxx hot band and its O-temper counterpart, but the aforementioned material parameters were found to assume very different values for the two hardness conditions of the aluminum alloy. Here we report on the initial findings of a further study on samples of the same alloy which resulted after the hot band was annealed at 500 deg F for 5 hours. Optical micrographs of the hot band and of the annealed sample did not reveal any observable difference in grain structure, and X-ray analysis showed that the annealing had no significant effect on the texture coefficients. Results of uniaxial tension tests indicated that the angular dependence of the q-value also remained essentially unchanged, but the material parameters which affect the directional properties of flow stress ~ were found to be much more sensitive to the heat treatment. Measurements by electron backscatter diffraction suggested that the annealing led to changes in the misorientation distribution and the emergence of subgrain structures.