Comparison of the Contributions of the Superplastic Deformation Mechanisms in Al-Mg-Fe-Ni-Zr-Sc Alloy with a Small Addition of Zn Processed by Rolling or Multidirectional Forging

Superplastic deformation is ensured by grain boundary sliding, which is accommodated by dislocation and diffusion creep. The contributions of these mechanisms depend on the microstructural parameters of alloys and temperature-strain rate conditions of deformation. In this work, the deformation behavior, grain structure parameters, and the contributions of the superplastic deformation mechanisms at the temperature 0.87Т_m and constant strain rate 1 × 10^–2 s^–1 were compared between the rolled Al-5Mg-0.9Fe-0.83Ni-0.14Zr-0.08Sc-0.72Zn alloy with the initial nonrecrystallized grain structure and the recrystallized alloy treated by multidirectional isothermal forging (MDF). The strain rate sensitivity coefficient was ~0.5, and the elongation reached 400–520% under the specified conditions. Superplastic deformation of the rolled alloy resulted in dynamic recrystallization providing strain weakening. In the MDF-treated alloy, deformation was accompanied by strain hardening due to grain growth. Regardless of the treatment mode, at the steady flow stage, the alloy shows similar microstructural parameters and similar contributions of the deformation mechanisms, which were determined from microstructural evolution on the surface with markers. The contribution of grain boundary sliding was ~40%, and intragranular dislocation slip/creep provided was ~20%. The remaining strain localized near transverse grain boundaries with the formation of striated zones, which were associated with grain boundary sliding and diffusion creep mechanisms.