The optical micrographs of the as-c

The optical micrographs of the as-cast (A), (B) and (C) alloys are shown in Fig. 1. It reveals that most precipitates distributed along the grain boundaries. The grain sizes of these alloys decrease with increasing Gd content. The average grain size of (C) alloy is 30–40 m, it is about half of (A) alloy. The XRD results of the as-cast alloys are shown in Fig. 2. It indicates that the (A), (B) and (C) alloys contain -Mg and -phase. In the previous work [10], it has been reported that the -phase is a stable phase and has been found in WE type alloys after solid solution treatment and a long time aging at over 250 ◦C. The -phase is eutectic phase and exists in both as-cast state and heat treatment and has fcc crystalline structure isomorphous with the Mg5Gd type.