CONSOLIDATION AND MECHANICAL-PROPERTIES OF ATOMIZED MG-BASED AMORPHOUS POWDERS

The newly developed ''clean process'' enabled safe atomization and consolidation of fine Mg-based alloy powders. An Mg85Cu5Y10 powder atomized at 923 K exhibited an amorphous phase in the particle size range smaller than 25 mum. A fully dense bulk amorphous Mg85Cu5Y10 alloy in the cylindrical form 6 mm in diameter was obtained by extrusion at 373 K below T(x). Amorphous Mg87.5Cu5Y7.5 powders (smaller than 25 mum) extruded at 673 K above T(x) had a mixed structure consisting of Mg24Y5 and Mg2Cu dispersed in an h.c.p. Mg matrix. The tensile strength for the bulk Mg87.5CuY7.5 alloy is 740 MPa at 298 K which is about twice as high as the highest value for conventional Mg alloys. The high strength is presumably due to the formation of the fine microstructure consisting of nanoscale intermetallic compound particulates homogeneously embedded in the Mg matrix with a fine grain size. The oxygen content of this alloy bulk produced by the ''clean process'' is 0.085 mass% which is half as low as the value for the bulk produced by the ordinary process in which the powders are exposed once in air. The tensile strength of the bulk extruded at an area reduction of 60% by the ''clean process'' is also about 43% as high as that for the bulk produced by the ordinary process. These data allow us to expect that the newly developed Mg-based alloys will proceed hereafter as a new type of high specific strength material.