MG-CU-Y AMORPHOUS-ALLOYS WITH HIGH MECHANICAL STRENGTHS PRODUCED BY A METALLIC MOLD CASTING METHOD

A low pressure casting of Mg-Cu-Y melts into copper molds was found to cause amorphous bulks in a cylindrical form. The maximum diameter of the amorphous cylinder (D(c)) shows a significant compositional dependence and reaches a maximum value of 4.0 mm for Mg65Cu25Y10. The compositional dependence of the D(c) is similar to that for the temperature span of the supercooled liquid region, DELTA-T(x)(= T(x)-T(g)). The similarity is presumably because the alloy with large DELTA-T(x) has a high resistance against the nucleation and growth of a crystalline phase resulting from the formation of a disordered structure with a more dense random packing and an optimum bonding states. The compressive proof stress at an elongation of 0.2% (sigma-p) for the Mg80Cu10Y10 cylinder was 822 MPa at room temperature and the fracture occurred along the shear plane. The sigma-p remains unchanged up to 350 K and then decreases significantly with increasing temperature, accompanied by the change in the deformation mode from inhomogeneous to homogeneous type. There is no appreciable difference in the features of mechanical strengths and deformation behavior between the bulk and ribbon samples, indicating the similarity of the disordered structure.