A Promising Approach to Solid-State Hydrogen Storage: Mechanical Nanostructuring Synthesis of Magnesium by High Pressure Torsion Extrusion

Abstract

This article presents an investigation into the impact of High Pressure Torsion Extrusion (HPTE) on the microstructural features, hardness and hydrogen storage, focusing on pure magnesium. HPTE is a modern mechanical nanostructuring technique that can refine the microstructural properties and subsequently affects the mechanical and functional properties of the materials. Two HPTE regimes were used in this study: (1) Direct Extrusion without rotation (DE), and (2) an extrusion speed of 6 mm/min along with a rotational speed of 1.8 rpm (v6w1.8). One sample in as-received conditions was also tested as a reference. Results showed increased hardness in the material after HPTE processing, with the DE sample reaching 60 HRB and the v6w1.8 sample exhibiting a gradient distribution of hardness from 71 to 83 HRB. X-ray diffraction analysis revealed significant microstructural refinement in the v6w1.8 sample. Results of hydrogenation kinetics showed that the DE sample absorbed up to 1.2 wt.% of hydrogen, while the v6w1.8 sample displayed 7.2 wt.% of hydrogen absorption, approaching the theoretical hydrogen storage capacity for magnesium (7.6 wt.%). These findings highlight the positive effects of HPTE on microstructural refinement and hydrogen storage, showcasing its potential for advancements in materials science and hydrogen-based energy technologies.