Mechanical mixing of Mg and Zn using high-pressure torsion

Abstract

High-pressure torsion (HPT) processing has proved to be a powerful tool to consolidate metallic particles and fabricate nanostructured metal-matrix composites with a wide range of compositions. In this study, HPT was used to fabricate different Mg-Zn composites at room temperature, and the evolution of microstructure and mechanical properties were analyzed by x-ray diffraction, scanning and transmission electron microscopy, dynamic hardness and Vickers microhardness tests. The results show that ultrafine-grained microstructures were achieved in all composites compositions. Smaller grain sizes are observed in Mg-rich phases near areas with significant segregations of Zn. The Mg-rich phase appears to retain less deformation than the Zn-rich phase. Bending and vortex phenomena, that are usually reported in microscale for materials mixed by HPT, are observed in nanoscale in this work. There is evidence of the MgZn2 intermetallic phase with a morphology that varies with composition. Higher levels of deformation imposed by HPT leads to an increase in hardening and a decrease in strain-rate sensitivity which are attributed to the tendency to form intermetallics and Zn segregations that prevent grain boundary sliding. Moreover, a model is proposed to explain the mixing of phases in microscale and its relation to the evolution of mechanical properties.