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alloys cylinders of millimeter scale thickness [Y. Li, K. Georgarakis, S.J. Pang, A. LeMoulec, T. Zhang, A.R. Yavari, unpublished research] were prepared.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 mu m 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 (C) 2008 Elsevier B.V. All rights reserved.