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

Abstract

A solid torsion sample made from AlMg3 (single phase Al alloy with 3 wt.% 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 {h k l} 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 {2 2 0} 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.