Characterization of the microstructure in Mg based alloy

Abstract

The cast products Mg–Sn based alloys are promising candidates for automobile industries, since they provide a cheap yet thermally stable alternative to existing alloys. One drawback of the Mg–Sn based alloys is their insufficient hardness. The hardenability can be improved by engineering the microstructure through additions of Zn to the base alloy and selective aging conditions. Therefore, detailed knowledge about the microstructural characteristics and the role of Zn to promote precipitation hardening is essential for age hardenable Mg-based alloys. In this work, microstructural investigation of the Mg–1.4Sn–1.3Zn–0.1Mn (at.%) precipitation system was performed using TEM. The chemical composition of the precipitates was analyzed using EDS. APT was employed to obtain precise chemical information on the distribution of Zn in the microstructure. It was found from microstructural studies that different precipitates with varying sizes and phases were present; lath-shaped precipitates of the Mg2Sn phase have an incoherent interface with the matrix, unlike the lath-shaped MgZn2 precipitates. Furthermore, nano-sized precipitates dispersed in the microstructure with short-lath morphology can either be enriched with Sn or Zn. On the other hand, APT analysis revealed the strong repulsion between Sn and Zn atoms in a portion of the analysis volume. However, larger reconstruction volume required to identify the role of Zn is still limited to the optimization of specimen preparation.