A comparative study of hydrogen storage properties of AZ31 and AZ91 magnesium alloys processed by different methods

We studied the hydrogen storage properties of commercial AZ31 and AZ91 magnesium alloys with refined microstructure. Various processing techniques, such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM), were utilized to modify the microstructure and phase composition of the alloys. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical digital microscopy (ODM) were utilized to characterise the microstructure and phase transformations during the hydrogen absorption/ desorption processes. The isothermal kinetics are measured by a Sieverts'-type apparatus at the tempera-ture of 350 celcius. In the ECAP process, the AZ31 alloy had a slightly higher storage capacity and faster ab-sorption kinetics, absorbing 6.0 wt% (6.6 wt% -maximum) of hydrogen in less than 12 min. In the HEBM process, AZ91 absorbed 6.5 wt% of hydrogen and desorbed it in 347 +/- 13 s, a faster rate than AZ31. The pressure-composition isotherms of all studied alloys at a temperature of 300 degrees C were determined. The processed alloys exhibited no pressure hysteresis. The microstructure of bulk samples and the morphology of prepared powders were shown to affect their hydrogenation behaviour. The activation energies for hy-drogen desorption were 119 +/- 2 kJ/mol for AZ31 alloy processed by ECAP and 128 +/- 3 kJ/mol for AZ91 alloy processed by HEBM, which are significantly lower than the activation energy values of pure Mg hydride. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the hydrogen storage properties of commercial AZ31 and AZ91 magnesium alloys with refined microstructure. Various processing techniques, such as equal channel angular pressing (ECAP) and high energy ball milling (HEBM), were used to modify the microstructure and phase composition of the alloys. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical digital microscopy (ODM) were employed to characterize the microstructure and phase transformations during hydrogen absorption/desorption processes. The results show that the processed alloys have enhanced hydrogen storage capacity and absorption/desorption kinetics. The isothermal kinetics of the alloys were determined using a Sieverts'-type apparatus at a temperature of 350 degrees Celsius.