Characterization of β precipitate phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy

As reported in our previous works, a Mg-7Gd-5Y-1Nd-0.5Zr alloy recently developed exhibited remarkable age-hardening responses and excellent mechanical properties at both room and elevated temperatures. In Mg-7Gd-5Y-1Nd-0.5Zr alloy, the β precipitate phase was assumed to be one of the main strengthening phases in peak-aged samples. This study aimed to determine the crystal structure and orientation relationship of the β precipitate phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy using transmission electron microscopy and high-resolution electron microscopy. The results indicated that the β precipitate had a face-centered cubic structure with a lattice parameter of a  =2.22 nm. The orientation relationship between the β precipitate phase and the α-Mg matrix was (1¯12)β//(1¯100)α,[110]β/[0001]α. The β plates formed on prismatic planes could play an important role in alloy strengthening by proving effective barriers to gliding dislocations. A single β plate often contained several domains of (11¯1)β twin-related variants. A composition of Mg5(Y0.4Gd0.4Nd0.2) was suggested for the β phase in Mg-7Gd-5Y-1Nd-0.5Zr alloy.

Graphical Abstract(a) HREM image of the β precipitate formed during 400°C ageing for 6 h along the [0001]α zone axis showing a single plate containing several domains of variants; (b) Corresponding SAED pattern of the β precipitate; (c) HREM image of the (11 1)β compound twinning boundaryFigure optionsDownload full-size imageDownload as PowerPoint slide