Study of intermetallics and phase equilibria of Mg–Zn–La system in Mg-rich corner at 345 °C

Abstract

Phase compositions, lattice structures and phase equilibria of Mg–Zn–La system in Mg-rich corner at 345°C have been investigated by equilibrated alloy method and diffusion couple technique. The results show that a binary solid solution of Mg12La is confirmed as (Mg,Zn)12La with 0–4.96at.% Zn. It has a body-centred tetragonal lattice structure with giant unit cell of a=b≈1.032nm and c≈7.748nm. Another linear ternary intermetallic (Mg,Zn)11La (Zn≈8.66–43.39at.%) has been identified too. (Mg,Zn)11La has a C-centred orthorhombic structure, and the unit cell of which becomes smaller with the increase of Zn content. The smallest lattice parameters of it are a≈1.1191nm, b≈0.9701nm and c≈0.9498nm. Both (Mg,Zn)12La and (Mg,Zn)11La are in equilibrium with Mg solid solution in their composition range. A three-phase equilibrium of Mg+(Mg,Zn)12La+(Mg,Zn)11La is also ascertained. In addition, MgZn phase containing about 1.53at.% La is confirmed, which is in equilibrium with Mg solid solution and (Mg,Zn)11La at 345°C. This result indicates that it is impossible for Mg17Zn21La2 reported in literature to be in equilibrium with Mg solid solution as a stable phase at this temperature.