Prominent role of basal slip during high-temperature deformation of pure Mg polycrystals

Abstract

Several controversies regarding the mechanical behavior of Mg at moderate temperatures and quasi-static strain rates remain unsolved. In particular, the fundamental reasons behind the anomalous grain size dependence of the flow stress during power law slip-dominated creep as well as of the observed decrease in the strain anisotropy with increasing temperature are still unknown. This work aims to shed light on these two issues by bringing new experimental evidence obtained by electron backscattered diffraction-aided slip trace analysis. Two pure Mg polycrystals, with average grain sizes (d) of 36 and 19μm, and similar textures and grain boundary misorientation distributions, were prepared by rolling and annealing, then subsequently tested in tension along the rolling direction at 150 and 250°C and at 10−3s−1. Their macroscopic mechanical response is related to the corresponding microstructure and texture evolution after straining, as well as to the frequency of slip traces corresponding to basal, prismatic and pyramidal 〈c+a〉 systems. This work highlights the prominent role of basal slip during high-temperature deformation of microcrystalline pure Mg and suggests that this enhanced basal activity might be key to rationalizing the two controversies under scrutiny. Furthermore, the current study attests to the impact on slip activity of grain size–texture correlations and of percolation between grains that are favorably oriented for basal slip during high-temperature deformation of pure Mg.