The dynamics of recrystallized grains during static recrystallization in a hot-compressed Mg-3.2Zn-0.1Ca wt.% alloy using in-situ far field high-energy diffraction microscopy

Abstract

The poor formability of rolled magnesium (Mg) alloy sheet remains a barrier to its widespread commercial use and is attributed to the strong basal texture that occurs in most mechanically processed Mg alloys. Recent attempts to successfully weaken the texture have been made using Mg-Zn-Ca alloys in combination with post-deformation annealing. The motivation for this work is to understand the evolution of the mesoscale processes that occur during annealing (specifically, static recrystallization) and lead to this texture weakening. Toward this goal, more than 1,200 recrystallized grains were studied during in-situ annealing in an 80% hot-compressed Mg-3.2Zn-0.1Ca wt.% (ZX30) alloy using far-field high-energy diffraction (ff-HEDM). The relative volume, crystallographic orientation, and position of each recrystallized grain emerging within a 1 × 1 × 0.1 mm3vol were tracked throughout static recrystallization. These measurements were used to quantitatively measure the nucleation and growth statistics associated with recrystallized grains as a function of annealing time. The measurements reflected a highly heterogeneous process with individual grain dynamics varying wildly from the average, and they also point to relations between relative grain volume and growth rate (or more accurately, the rate of change of volume) with a peak average rate occurring early in recrystallization (at 22% recrystallized). We also explore whether a recrystallized grain's current state can be used to predict its future growth behaviors with implications for Monte Carlo simulations. Finally, we investigate whether recrystallized grains with specific orientations have preferential nucleation and/or growth, and we find that grains with a weak basal texture have a pronounced nucleation advantage that increases with annealing time, while other grain orientations have a slight growth advantage that diminishes with annealing time.