MECHANICAL ANISOTROPY AND DEFORMATION MECHANISMS IN AN AL-CU-ZR SUPERPLASTIC ALLOY

Severe mechanical anisotropy of deformation is reported for a superplastic Al6Cu0.3Zr alloy. This anisotropy is a function of strain and strain-rate, decreasing with increasing strain and increasing with decreasing strain-rate until a certain limiting value is reached at any given strain. By use of the quantitative texture measurements reported in the preceding paper it has been possible to predict the anisotropy of deformation expected from two given slip mechanisms, and in this way to identify the operative mechanisms by a comparison with measured results. At the high strain-rates calculations based on the assumption of multiple slip lead to correctly predicted anisotropies, whilst at the lower strain-rates a progressively worsening fit is obtained. This is identified with a decreasing slip contribution to the overall strain, and with the anisotropy increasing to a value characteristic of grain boundary sliding in the banded structure. The decrease in anisotropy observed with strain is explained in terms of the break-up of this banded structure and the creation of equiaxed grains. It is thus shown for the first time that mechanical anisotropy measurements can not only indicate a change in the dominant deformation mode, but that, if coupled with accurate texture measurements, they can also assess the varying role of crystallographic slip in a deformation process. © 1979.