HIGH MECHANICAL STRENGTHS OF MG-NI-Y AND MG-CU-Y AMORPHOUS-ALLOYS WITH SIGNIFICANT SUPERCOOLED LIQUID REGION

Mg-Ni-Y and Mg-Cu-Y alloys were found to form an amorphous solid in wide compositional ranges of 0 to 40 at%Ni or Cu and 0 to 40% Y by the melt spinning technique. These amorphous alloys exhibit a wide supercooled liquid region before crystallization and the glass transition temperature (T(g)) increases from 398 to 568 K with increasing Y content, while a minimum at about 15%Ni or Cu is seen in the changes of T(g) with Ni or Cu content. The temperature span DELTA-T(x)( = T(x)-T(g) shows a maximum around the central composition in the range where the glass transition is observed and the largest DELTA-T(x) is 41 K for Mg50Ni30Y20 and 61 K for Mg65Cu25Y10. Furthermore, the Mg-based amorphous alloys containing above about 70% Mg have a good bending ductility and the tensile fracture strength (sigma-f) reaches 830 MPa for Mg80Ni15Y5 and 800 MPa for Mg85Cu5Y10. The specific strength defined by the ratio of sigma-f to density is 3.5 x 10(5) N.m/kg for both alloys which is about 2.0 times as high as the highest value for conventional Mg-based crystalline alloys. The Mg-based amorphous alloys are attractive as a new type of high-strength material with light weight.