AlNiY chill-zone alloys with good mechanical properties

Using cold graphite mold casting method, Al-based chill-zone alloys cylinders of millimeter scale thickness [Y. Li, K. Georgarakis, S.J. Pang, A. LeMoulec, T. Zhang, A.R. Yavari, unpublished research.] were prepared. Using high-resolution scanning electron microscopy (HRSEM), it was found that hard submicron crystalline surface layers of thickness about 200 μm form when the melt can be undercooled. The structure and the thermal properties of the chill-zone alloy were examined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). A metastable phase Al₁₉Ni₅Y₃ nucleated during cooling then transformed to equilibrium intermetallics after annealing. The chill-zone alloy shows high mechanical strength in excess of 1 GPa at high ambient temperatures and good plasticity. The combination of high strength and good plasticity will be discussed in relation to the special structure of the chill-zone alloy.