Phenomenological Model for the Dynamic Superplastic Deformation Mechanism in a Zn-Al Eutectoid Alloy Modified with 2 wt% Cu

In this work, superplastic behavior in tension for the Zn-21Al-2Cu alloy was reviewed as a function of: grain size, temperature and strain rate. The deformation mechanism was studied under conditions where the greatest elongation was reached, characterizing microstructural changes and analyzing the associated mechanical response such as the study of plastic stability. This analysis allowed us to propose a phenomenological model consisting of five steps for the mechanism of superplastic deformation under which dynamic conditions are involved for this alloy. In the first stage, an accommodation of the microstructure was observed, in the second stage sliding by individual grain boundaries (GBS) was activated, which provided the conditions for stationary plastic flow. In the third stage, GBS was hampered by the tendency of grain boundaries remaining from high temperature phase (FβBs) to align at 45°. This fact caused the onset of plastic instability. The fourth stage consisted of a transition in which there was competition between individual and cooperative GBS mechanisms, which increased plastic instability. In the last stage, the FβBs were aligned parallel to tensile direction, which favored the GBS, and an additional diffusion flow mechanism allowed partial recovery of stable plastic flow.

Graphical Abstract