Stable icosahedral phase in Mg44Zn44Gd12 alloy

The microstructure of the as-cast Mg44Zn44Gd12 alloy was investigated by using X-ray diffraction (XRD), differentical scanning (DSC), scanning electron microscopy (SEM) and a detailed transmission electron microscope. The XRD, DSC and SEM results indicated that the as-cast Mg44Zn44Gd12 alloy were mainly composed of three types of phases: the primary solidification phase, the dendritic phase and the eutectic phase. The primary solidification phase had an icosahedral structure. The dendritic phase was the W-phase, and eutectic structure phase was the Mg7Zn3 phase. Microstructures of icosahedral phase (I-phase), W-phase and Mg7Zn3 phase in Mg44Zn44Gd12 alloy were investigated. The results indicated that the I-phase in Mg44Zn44Gd12 alloy was a face-centered icosahedral quasicrystal with stoichiometric composition of Mg42Zn50Gd8 which had an excellent thermal stability up to 420 °C. The solid solution of the Gd gradually decreased during solidification, which played an important role in activating the formation of Mg7Zn3 phase and W-phase from icosahedral phases.