Effect of the addition of 1.5 wt.% of mischmetal in the ZK60 alloy processed by Friction Stir Process (FSP) followed by filing on the H-absorption/desorption kinetics

Abstract

This work investigates the application of Friction Stir Process (FSP) to the ZK60 alloy enhanced with 1.5 % mischmetal (ZK60–1.5 wt% Mm) combined with manual filing to achieve significant improvement in the hydrogen storage properties of this alloy. Addition of 1.5 wt% Mm to the ZK60 alloy yields a matrix with high thermal stability, attributable to the formation of high melting point intermetallic phases. Post FSP, the ZK60–1.5 wt% Mm material shows a refined, pulverized, and recrystallized structure. Such a structure allows the acquisition of filings with nanometric particle sizes and even more pulverized intermetallic phases post-FSP. This synergistic approach produces a significantly homogeneous microstructure morphology, facilitating the study of the catalytic role Mm plays in the hydrogen storage kinetics of the ZK60 alloy at 350 °C. Currently, among all Severe Plastic Deformation (SPD) techniques, only FSP followed by manual filing has demonstrated a capacity to provide a nanometric, homogeneous microstructure that significantly enhances hydrogen storage kinetics and cycling properties. Additionally, the combination of FSP and manual filing is an industrialization process that can be easily implemented, offering reliability, controllability, and cost-effectiveness compared with alternative methods like High-energy Ball Milling (HEBM). Experimental kinetic data for (de)hydrogenation reactions were analyzed using the Luus-Jaakola optimization method, underscoring the potential applicability of the FSP-manual filing route for hydrogenation temperatures <350 °C.