Determination of the radial crystallite microstrain distribution within an AlMg3 torsion sample using monochromatic synchrotron radiation

A solid torsion sample made from AlMg3 (single phase Al alloy with 3wt.% Mg) is strongly plastically deformed in three steps of Δγ1=1.5, Δγ2=1, and Δγ3=1 to a total deformation of γ=3.5. The low speed deformation is carried out at room temperature with free ends. After each deformation step, the residual strain and texture within the sample are characterized non-destructively by a three-dimensional diffraction technique using monochromatic high energy synchrotron radiation.

The macrostrain tensor is determined as a function of the radial position and the deformation by fitting the distortion of complete diffraction rings. Systematic deviations of the {hkl} specific diffraction ring distortions from the fit are interpreted as crystallite microstrains. These strains are in the order of (480–1550)×10−6.

A comparison to results from crystallite microstrain measurements on uni- and bi-axially deformed samples shows that particularly the Al {220} reflection exhibits dramatically higher crystallite microstrains for tri-axial deformation obtained by solid torsion. This proves that crystallite microstrains cannot be neglected when deformations are bi- or tri-axial.

In the deformation-dependent texture development, an increasing dominance of ideal torsion texture orientation A1* over A2* is observed. No evidence is found for ideal orientation B.