MG-CU-Y BULK AMORPHOUS-ALLOYS WITH HIGH-TENSILE STRENGTH PRODUCED BY A HIGH-PRESSURE DIE-CASTING METHOD

Amorphous Mg-Cu-Y alloys with diameters (or thicknesses) ranging from 1 to 7 mm were formed in cylinder and sheet forms by using a high-pressure die casting process. The maximum diameter (or thickness) for formation of an amorphous phase was strongly dependent on composition and the largest value was obtained for Mg65Cu25Y10. There is a tendency for the maximum diameter to increase with-an increase in the supercooled liquid region. The glass transition temperature, crystallization temperature and heat of crystallization are independent of sample diameter in the range below 7 mm while the heat of relaxation decreases with increasing sample diameter, indicative of the formation of a more relaxed atomic configuration in the thicker samples. The tensile strength (sigma(f)) of the cast Mg80Cu10Y10 alloy is 630 MPa at room temperature (RT), remains almost unchanged in the range below 353 K and then decreases to 395 MPa at 423 K, accompanying the significant increase in elongation. The sigma(f) at RT is about 80% as high as that for the corresponding melt-spun ribbon and the difference is presumably due to the existence of pores which are evaluated to be about 17%. It is thus concluded that the application of the high-pressure die casting technique to the alloys with large glass-forming ability is useful for the formation of the bulk amorphous alloys with high tensile strength.