Zn segregation at precipitate/matrix interface in Mg–Sn–Zn alloys

Abstract

Magnesium-tin based alloys have received considerable attention in the past 15 years for developing high strength alloys. Mg–Sn binary alloys are precipitation hardenable, but their age-hardening response is moderate. Additions of Zn can significantly improve the age-hardening response of binary Mg–Sn alloys by refining the distribution of Mg2Sn precipitates. To understand the role of Zn in the precipitation process, Mg2Sn precipitates with different morphologies and orientations in under-, peak- and over-aged samples of a Mg–9.8Sn–1.2Zn (wt%) alloy are characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and STEM X-ray mapping. It is found that Zn atoms always segregate to the precipitate-matrix interface, irrespective of the interfacial structures and orientation relationships of the Mg2Sn precipitates. This finding provides an insightful clue to the understanding of the enhanced nucleation and thermal stability of Mg2Sn precipitates in the Mg–Sn–Zn alloys.