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

Phase compositions, lattice structures and phase equilibria of Mg-Zn-La system in Mg-rich corner at 345 degrees 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)(12)La with 0-4.96 at.% Zn. It has a body-centred tetragonal lattice structure with giant unit cell of a = b approximate to 1.032 nm and c approximate to 7.748 nm. Another linear ternary intermetallic (Mg,Zn)(11)La (Zn approximate to 8.66-43.39 at.%) has been identified too. (Mg,Zn)(11)La 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 approximate to 1.1191 nm, b approximate to 0.9701 nm and c approximate to 0.9498 nm. Both (Mg,Zn)(12)La and (Mg,Zn)(11)La are in equilibrium with Mg solid solution in their composition range. A three-phase equilibrium of Mg+(Mg,Zn)(12)La+(Mg,Zn)(11)La is also ascertained. In addition, MgZn phase containing about 1.53 at.% La is confirmed, which is in equilibrium with Mg solid solution and (Mg,Zn)(11)La at 345 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.