HIGH-STRENGTH CRYSTALLINE ALUMINUM-ALLOYS PRODUCED FROM AMORPHOUS POWDER BY A CLOSED P/M PROCESSING

A closed processing system for preparation and consolidation of amorphous alloy powders has been developed. The sequent steps can be carried out under a well-controlled atmosphere in which the oxygen and moisture components less than 1 ppm. For an Al85Ni5Y8Co2 (at%) amorphous alloy which has the highest tensile strength (1250 MPa) in the Al-based amorphous alloys, the crystallized bulks have been produced by extrusion of the amorphous powder. Their mechanical properties have been examined and compared with those produced by the ordinary processing. In the case of the ordinary processing, the tensile strength of the bulky sample produced at reduction in cross-sectional area (RA) of 90% (10:1 in extrusion ratio) is 900 Mpa at room temperature and 480 MPa at 573 K. These values are much higher than those of conventional powder metallurgy (P/M) aluminum alloys. Furthermore, the tensile strength of the bulks are improved by the closed processing due to the decrease in the thickness and the amount of residual hydrate of the surface oxide layer on the powder particles. It was found that the tensile strength of the crystallized bulk produced by extrusion at RA of 90% is 60 MPa higher at 573 K and the room-temperature tensile strength of the bulk prepared by extrusion at small RA of 60% (2.5:1 in extrusion ratio) is 240 MPa higher than that produced by the ordinary processing. It is concluded that the closed processing is useful to produce high-strength P/M alloys with a large scale by consolidation at a smaller degree of hot working, and the crystallization of an amorphous phase is effective as a structural modification method to produce high-strength materials.