Texture effects and rate-dependent behaviors of notched magnesium bars

Abstract

It is known that the mechanical behavior of many hexagonal close-packed (HCP) materials is sensitive to textural variations. In the technologically important magnesium (Mg) alloys, the anisotropic plastic behaviors and their dependence on different processing-induced textures have been reasonably well studied under relatively simple stress states. However, a detailed assessment of the rate-dependent microstructure–property linkages under triaxial stress states is relatively less explored. In this work, we present a computational investigation of the role played by strain rate, texture, and stress state in the macro–micro mechanical characteristics of Mg alloys. Three-dimensional boundary value problems using smooth and notched round bar geometries subjected to tensile deformation are modeled using a crystal plasticity framework that includes slip and twinning deformation mechanisms. We examine the responses over six orders of magnitudes of strain rates, for three different initial textures that span a broad spectrum of textural strengths, and three specimen geometries that induce varying levels of stress triaxiality. The simulations reveal a remarkable transition of the tensile response from a conventional power-law type to a sigmoidal type for certain combinations of textures, stress triaxiality levels, and strain rates. While the stress response is strongly rate-dependent, the macroscopic deformation anisotropy has a negligible effect from strain rate compared to the role of the stress state and texture. We discuss the potential implications of these observations on the rate-dependent failure of Mg alloys.