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Dendritic evolution during coarsening of Mg-Zn alloys via 4D synchrotron tomography

Guo, E; Phillion, AB; Cai, B; Shuai, S; Kazantsev, D; Jing, T; Lee, PD; (2017) Dendritic evolution during coarsening of Mg-Zn alloys via 4D synchrotron tomography. Acta Materialia , 123 pp. 373-382. 10.1016/j.actamat.2016.10.022. Green open access

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Abstract

The scale of solidification microstructures directly impacts micro-segregation, grain size, and other factors which control strength. Using in situ high speed synchrotron X-ray tomography we have directly quantified the evolution of dendritic microstructure length scales during the coarsening of Mg-Zn hcp alloys in three spatial dimensions plus time (4D). The influence of two key parameters, solute composition and cooling rate, was investigated. Key responses, including specific surface area, dendrite mean and Gauss curvatures, were quantified as a function of time and compared to existing analytic models. The 3D observations suggest that the coarsening of these hcp dendrites is dominated by both the re-melting of small branches and the coalescence of the neighbouring branches. The results show that solute concentration has a great impact on the resulting microstructural morphologies, leading to both dendritic and seaweed-type grains. It was found that the specific solid/liquid surface and its evolution can be reasonably scaled to time with a relationship of ∼ t−1/3. This term is path independent for the Mg-25 wt%Zn; that is, the initial cooling rate during solidification does not greatly influence the coarsening rate. However, path independence was not observed for the Mg-38 wt%Zn samples because of the seaweed microstructure. This led to large differences in the specific surface area (Ss) and its evolution both between the two alloy compositions and within the Mg-38 wt%Zn for the different cooling rates. These findings allow for microstructure models to be informed and validated to improve predictions of solidification microstructural length scales and hence strength.

Type: Article
Title: Dendritic evolution during coarsening of Mg-Zn alloys via 4D synchrotron tomography
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.actamat.2016.10.022
Publisher version: http://dx.doi.org/10.1016/j.actamat.2016.10.022
Language: English
Additional information: Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Keywords: Magnesium alloy, Semi-solid, X-ray tomography, Coarsening, Dendrite
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10049108
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