Lath-like phases formed at an extremely high temperature in a Mg-RE(RE=rare earth)-Al alloy

Thermal stable intermetallic particles are important for the heat resistance of magnesium（Mg）alloys.In this work,many lath-like particles formed in α-Mg grains of a Mg-8Gd-3Sm-0.7Al casting alloy when heat-treated at 873 K.Atomic-resolution high-angle annular dark field scanning transmission electron microscopy（HAADF-STEM） characterizations indicate that most of them are Mg-containing Al2（Gd,Sm）,with the atomic ratio of Mg:Al:（Gd,Sm） being ～1:1:1;a small part of them with relatively wider thickness are long-period stacking ordered（LPSO） phases simultaneously containing both 14H and 18R structures.Both followed common orientation relationships with Mg matrix as those reported in previous work.In addition,many Mg laths were observed in the primary blocky Al2（Gd,Sm） phase at grain boundaries,where the atomic ratio of Al:（Gd,Sm） in the Al2（Gd,Sm） matrix was 2:1.Finally,density functional theory（DFT） calculations illustrated the detail structure of the re-constructed Mg/Al2RE interface and simultaneously deduced the underlying reason for the re-dissolution of the newly formed Mg-containing Al2（Gd,Sm） plates in α-Mg matrix.