Evolution of phase morphologies, compositions, structures of Mg-Y-Nd system with Sm addition

Abstract

In this study, the evolution of phase morphologies, compositions, structures of Mg-Y-Nd system with Sm addition were investigated. The microstructure of the as-cast alloy consists of a Mg-matrix, Mg24Y5 (bcc structure, a = 1.1250 nm), and Mg5(Y0.7Nd0.1Sm0.2) (fcc structure, a = 2.2472 nm) phases. After a solution treatment, the eutectic phases are substantially dissolved into the Mg-matrix. A large amount of β′ precipitates are dispersed and precipitated in the grain after a T6 heat treatment, and the orientation relationships between β′ precipitates and Mg-matrix are (0 0 1)β′ || (0 0 0 1)Mg, (0 2 0)β′ || (101¯0)Mg, [1 0 0]β′ || [011¯0]Mg. Furthermore, the quadrate phases indexed as Mg6Y3(Nd0.8Sm0.2)1, Mg6Y3(Nd0.2Sm0.8)1, and Mg10Y5(Nd0.2Sm0.8)1 are observed in various heat treatment states, which are fcc structures and their lattice parameters are a = 0.5318 nm, a = 0.5319 nm, a = 0.9894 nm, respectively. Keywords: Mg-Y-Nd-Sm-Zr, Phase evolution, TEM