Metallurgical Abstracts on Light Metals and Alloys vol.56

HRTEM Characterization of an Age-Hardened Mg–Ca Binary Alloy

Mariko Unekawa* and Yoshihiro Terada*
* Department of Materials Science and Engineering, Tokyo Institute of Technology

[Published in Materials Transactions, Vol. 64 (2023), pp. 613–616]

https://doi.org/10.2320/matertrans.MT-M2022039
E-mail: terada.y.ab[at]m.titech.ac.jp
Key Words: Magnesium–calcium alloy, Mg₂Ca, Aging, Coherency, HRTEM

A Mg–2.8 mass% Ca binary alloy was subjected to a homogenization treatment. The three-dimensional morphology and coherency of the Mg₂Ca phase (with C14 structure), which precipitated in the primary α-Mg dendrite, were investigated for the specimens aged at 423 K. The Mg₂Ca precipitate exhibited a hexagonal plate-like morphology, with a planar surface that is parallel to the (0001)_α basal plane and sides that are parallel to the {-1010}_α columnar plane of the α-Mg matrix. The coarsening Mg₂Ca precipitate retained coherency with the α-Mg matrix for aging time of 3 h, which corresponded to the peak-aged condition. Furthermore, during the coarsening process, misfit dislocations were introduced on the planar surface of the precipitates, and the coherent interface became a semi-coherent interface for aging time of 100 h, which corresponded to the over-aged condition. The Mg₂Ca precipitates evolved from a hexagonal plate-like morphology to a rectangular morphology and then to a polygonal morphology during aging treatment at 423 K.

Figure HRTEM image of the Mg–2.8 mass% Ca alloy aged at 423 K for 3 h, taken with B = [11-20]_α (a). The C14-Mg₂Ca precipitate was taken with B = [1-21-3]_α (b).