Amorphous magnesium-rich alloys Mg y X 1Ϫy (X ϭ Ni or Cu and 0.82 Ͻ y Ͻ 0.89) have been produced by melt spinning. The crystallization kinetics of these alloys have been determined by in situ X-ray diffraction (XRD) and isothermal and isochronal differential scanning calorimetry (DSC) combined with ex situ XRD. Microstructure analysis has been performed by means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Crystallization of the Mg-Cu alloys at high temperature takes place in two steps: primary crystallization of Mg, followed by simultaneous crystallization of the remaining amorphous phase to Mg and Mg 2 Cu. Crystallization of the Mg-Cu alloys at low temperatures takes place in one step: eutectic crystallization of Mg and Mg 2 Cu. Crystallization of the Mg-Ni alloys for a Mg content, y Ͼ 0.85, takes place in two steps: primary crystallization of Mg and of a metastable phase (Mg ϳ5.5 Ni, with Mg content y ϭ 0.85), followed by the decomposition of Mg ϳ5.5 Ni. Crystallization of the Mg-Ni alloys for a Mg content y Ͻ 0.85 predominantly takes place in one step: eutectic crystallization of Mg and Mg 2 Ni. Within the experimental window applied (i.e., 356 K Ͻ T Ͻ 520 K and 0.82 Ͻ y Ͻ 0.89), composition dependence of the crystallization sequence in the Mg-Cu alloys and temperature dependence of the crystallization sequence in the MgNi alloys has not been observed.

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