Correlation of milling time with phase evolution and thermal stability of Mg-25 wt%Sn alloy

Abstract Mg-25Sn (wt%) mixtures were prepared by mechanical alloying (MA), and then cold-compacted into preforms. Correlation of milling time with phase evolution during MA and their thermal stability in the subsequent heating-up process was investigated. The raw nano-sized Sn powder is conductive to the accelerated synthesis of Mg2Sn phase, by which nano cubic and hexagonal Mg2Sn could be obtained after 5 h and 20 h MA, respectively. During the heating process, the residual Sn in the short-time ball milling (5 h, 10 h) transforms mainly into Mg2Sn bulk through melting and subsequent diffusion reactions. However, the 20 h MAed mixture has experienced inverse eutectic and subsequent thixotropic reactions, in which metastable-to-equilibrium transition of Mg2Sn occurs. Mg2Sn phase formed in the two cases are nanosized. A uniform dispersion of fine Mg2Sn phase and the retention of inverse eutectic liquid phase primarily account for the improvement in mechanical properties of the sintered material.