Revisiting tension-compression asymmetry in a Mg alloy: insights from statistical strain partitioning and intra-/inter-granular mechanisms at the nanoscale

Abstract

Tension-compression asymmetry (TCA) is a fundamental mechanical characteristic in Mg alloys. However, its underlying integrated intra- and inter-granular deformation modes and the corresponding nanoscale strain partitioning remain unclear. In this work, the nanoscale strain partitioning together with the activity of both the individual slip modes and apparent grain boundary sliding/shear (GBS), in terms of tangential displacement along the grain boundaries (GBs), were quantitatively and statistically investigated based on approximately 200 grains analyzed for an aged, twin-free Mg-10Y sheet during tension and compression. This was accomplished using multimodal analysis of high-resolution digital image correlation (HRDIC) and electron backscattered diffraction (EBSD) data. The results revealed that strain partitioning exhibited pronounced TCA, where the mean and maximum effective shear strain (ε_eff) values of both slip bands (SBs) and the grain mantle (GM, the region near grain boundary) for tension were larger than that for compression, implying more intensive strain localization in tension. TCA was also evident from analysis of the relative slip activity for the various slip modes, where pyramidal 〈c + a〉 slip was barely activated during tension, but it exhibited a relatively high activity during compression. The GBS activity, which was quantified in terms of both the apparent GBS displacement and the participation rate, was higher for tension compared with compression. This work, which provided experimental and quantitative evaluation of asymmetric strain partitioning and GBS for the first time, adds valuable information useful for a more complete understanding of TCA in polycrystalline Mg alloys.