Eutectic structure and bulk glass formation in Mg-based alloys

The glass forming abilities (GFA) of Mg65Cu25−xY10Nix alloys were investigated by copper mold casting. The evolution of microstructure of master alloys and the structures of as-cast alloys were checked by optical microscopy, X-ray diffraction and differential scanning calorimeter. It was found that the highest GFA was not exactly at the eutectic point of the Mg65Cu25Y10 alloy according to the melting temperature analyzed. Mg65Cu25Y10 revealed a dendrite microstructure while Mg65Cu22Ni3Y10 exhibited a eutectic microstructure that had a relatively high GFA. The deviation of eutectic microstructure and the deviation of the best GFA composition from the eutectic point can be explained in terms of a skewed coupled eutectic zone, and the higher glass-transition temperature on the hypereutectic side.