Investigation on the Mechanical Properties of Polycrystalline Mg Using Molecular Dynamics Simulation

Abstract

Magnesium (Mg) and its composites have been widely used in different fields, but the mechanical properties and deformation mechanisms of polycrystalline Mg (polyMg) at the atomic scale are poorly understood. In this paper, the effects of grain size, temperature, and strain rate on the tensile properties of polyMg are explored and discussed by the Molecular dynamics (MD) simulation method. The calculated results showed that there exists a critical grain size of 10 nm for the mechanical properties of polyMg. The flow stress decreases with the increase of grain size if the average grain size is larger than 10 nm, which shows the Hall-Petch effect, and the deformation mechanism of large grain-sized polyMg is mainly dominated by the movement of dislocations. When the average grain size is less than 10 nm, it shows the reverse Hall-Petch effect that the flow stress decreases with the decrease of grain size, and the deformation mode of polyMg with small grain-size is the movement and deformation of atoms at the grain boundary. Due to the more active motion of atoms as the system temperature increases, the material can easily reach the plastic stage under tensile loading, and the mechanical properties of polyMg decrease at high temperatures. The strain rate has a hardening effect on the properties of composite. Based on our calculated results, it can provide theoretical guidance for the applications of Mg metal and Mg matrix composites.