Low temperature rolling of magnesium alloys for hydrogen storage

Referencia Apresentador Autores
Wágner Batista Silva Silva, W.B.(Universidade Federal de São Carlos); Leiva, D.R.(Universidade Federal de São Carlos); Silva, E.P.(Universidade Federal de São Carlos); Ishikawa, T.T.(Universidade Federal de São Carlos); Botta, W.J.(Universidade Federal de São Carlos); Figueroa, S.J.(Laboratório Nacional de Luz Síncrotron); In this study, SPD was applied by low temperature rolling in order to make efficient the use of solid materials in substitution of the ground powder materials, which require hours of processing, making it expensive and subject to high reactivity when ground. We submitted samples of pure Mg, AZ91, and ZK60 + 2,5wt.% Mm to low temperature rolling (LTR). Equal channel angular pressing (ECAP) was used as a previous processing step to refine the microstructure. Some samples were submitted to rolling passes at room temperature after cooling in liquid nitrogen, until a typical thickness between 0.1 and 0.2 mm was obtained. Two different rolling conditions were applied: by cold rolling at room temperature (CR) and LTR with the immersion of the alloys in liquid nitrogen for a period of three minutes after each pass. TEM analysis revealed that the addition of Mm to ZK60 alloy has contributed to generating finer grain microstructure if compared to the pure magnesium. In the ZK60 + 2.5wt.% Mm alloy, crystallites usually are smaller than 1 ?m. X-ray microtomography results show that ECAP+LTR is more effective than ECAP+CR to generate cracks, an aspect that is useful for hydrogen storage materials. The results of XPS showed that ZK60 + 2.5% Mm exhibited better resistance to the formation of oxides and hydroxides and consequently a larger free area of these contaminants. The highly refined microstructure of the ECAP+LTR samples, combined with the presence of strong (002) texture and adequate morphology result in interesting activation kinetics at 350ºC and 20 bar of H2. The most deformed state, the greatest amount of defects and grain boundaries that is introduced with the processes of LTR guaranteed the best storage property gains in relation to capacity, activation and H2 absorption/desorption kinetics.
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