Comparative studies of grain refinement of commercial purity Mg by CaO and Ca addition

ABSTRACT

The comparative studies of grain refinement of commercial purity Mg by CaO/Ca addition have been investigated by using TP-1 tests, optical microscope, XRD characterisation and TEM (STEM) observation along with EDX analysis. Experimental results showed that Ca/CaO addition significantly refines the grain structure of commercial purity Mg. Compared with Ca addition, CaO exhibits finer grain size and the average grain size remains invariable with further CaO addition. CaO addition is readily reduced to Ca by Mg melt and forms Mg₂Ca on the surface of MgO particles. First-principle calculations were used to understand the nucleation of Mg₂Ca layer by a coherent interface model calculating the work of adhesion and the interface energy between Mg₂Ca and α-Mg. The combination of experiments and calculations showed that the formation of Mg₂Ca layer on MgO facilitates the nucleation of α-Mg and then refines the grain structure by Ca or CaO addition.

KEYWORDS:

• Heterogeneous nucleation
• magnesium
• grain refinement
• Ca
• CaO

Acknowledgements

This work is financially supported by Anhui Provincial Natural Science Foundation (1808085ME123), the Projects of International Cooperation and Exchanges in Anhui Provincial Key Project of Research and Development Plan (1804b06020363), the Key University Science Research Project of Anhui Province (KJ2017A054), Priority Funding Scheme for Innovative Projects for Overseas Chinese Students in Anhui Province, EPSRC under grant numbers of EP/H026177/1 for the EPSRC Centre – LiME and EP/I038616/1 for the TARF-LCV programme.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the University Natural Science Research Project of Anhui Province [1808085ME123].