Effect of long-term room-temperature storage on the structure and properties of glassy melt-spun Mg-Al-Ca alloys

The effects of 48 months storage at room temperature on the structure and properties of glassy melt-spun Mg-Al-Ca alloys has been determined. The results show that while Knoop hardness does not differ significantly from values obtained shortly after melt spinning, x-ray diffraction (XRD) shows considerably stronger signals from αMg present in the glassy matrix, detected only for the most dilute glass forming composition some months after melt spinning. High-resolution electron microscopy (HREM) studies show the presence of nanocrystallites in the glassy matrix with interplanar spacings matching αMg, and energy-dispersive spectroscopy (EDS) indicates the presence of Al and Ca within these nanocrystallites. Differential scanning calorimetry (DSC) studies at 20, 40, and 80 K/min show evidence of two-stage crystallization with the first stage starting at approximately 120 deg with a peak at approximately 150 °C and the second stage peaking at approximately 250 °C. The significance of these results is discussed.