X-ray microtomography was used to observe hydrogen micropores and their growth behavior at high temperatures in several aluminum alloys. High-density micropores were observed in highpurity Al-Mg alloys, but their density and volume fraction were much lower in pure aluminum. Our results have revealed that the growth behavior of micropores is dominated by Ostwald ripening. About 53 % of hydrogen is trapped in micropores in Al-Mg alloy with low hydrogen content, making micropores the predominant hydrogen trap site. Although total hydrogen content is similar to that in the alloy, the ratio of hydrogen trapped in micropores is below 7 % in pure aluminum. This difference is attributable to the lack of hydrogen precipitation sites in pure aluminium.Although the overall amounts of hydrogen at dislocations and grain boundaries are small in all the materials, the occupancies for these trap sites were concluded to be very high.

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