Abstract
Mg alloys containing high Gd are featured by the outstanding aging hardening response. Here we conduct a systematic study on the hardening behavior and precipitation evolution in a Mg10Gd alloy during isothermal aging at 200–250 °C by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The optimum aging temperature of Mg10Gd is 200 °C with peak hardness of 102.4 HV. Hardness improvement of the aged samples at 200 °C mainly originates from precipitation strengthening, and β’ nano-precipitates with fine size of 10 nm are the main strengthening phases. The samples exhibit a certain aging hardening effect at 225 °C with peak hardness of 89.4 HV, due to the gourd-shaped β’ precipitates with coarse size of 100 nm. Furthermore, various metastable nanoscale structures (including short-range ordered GP zones, β”, βT, βM and βF′ phases) are observed in the aged samples, and their formation mechanisms are rationalized in detail.
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