Hall-Petch relationship and deformation mechanism of pure Mg at room temperature

Abstract

According to the well-known Hall-Petch theory, grains refinement is one of the most effective routes to improve the mechanical properties of Mg. Understanding the Hall-Petch relationship of Mg can provide guidance for improving the mechanical strength of Mg through grain refinement. In this study, pure Mg samples with average grain sizes ranging from 9.8 µm to 31 nm were prepared, and the grain size dependence of the deformation microstructure, dislocation density, strain rate sensitivity, activation volume and mechanical properties were investigated. Moreover, the Hall-Petch relationship of pure Mg and the mechanism that caused the transformation of the Hall-Petch relationship were explored. It is found that there are three Hall-Petch relationships for pure Mg: positive correlation with large stress concentration factor and the dominated deformation mechanism of twin (>2.4 µm), positive correlation with small stress concentration factor and the dominated deformation mechanism of dislocation (between 2.4 µm and 93 nm) and an inverse correlation with negative stress concentration factor and the dominated deformation mechanism of GB motion (<93 nm). • Pure Mg with grain sizes ranging from 9.8 µm to 31 nm was prepared. • The Hall-Petch curve of pure Mg can be divided into three regions according to the slope and two critical grain sizes. • Three micromechanics are dominating the deformation of pure Mg at room temperature.