STRUCTURES AND PROPERTIES OF RAPIDLY SOLIDIFIED MG-CA BASED ALLOYS

With the aim of developing new light weight and high strength materials, rapidly solidified flakes of Mg-Ca based alloys with or without ternary additions such as Zn, Si and Ce were produced by atomizing the alloy melt and subsequent splat-quenching on a water-cooled copper roll. The flakes were consolidated by hot extrusion. Metallographic structures and constituent phases were examined for both rapidly solidified flakes and powder metallurgical (PM) materials, and mechanical properties were evaluated for PM materials. The rapidly solidified flakes show fine dendritic cell structures with the cell size ranging from 0.2 to 2 mum. Hardness increased on heating the flakes of Mg-Ca binary alloys at 373-473 K, presumably due to precipitation Of Mg2Ca from extended solid solution of Ca in Mg. No such hardness increase is observed in the ternary alloys. After consolidation, fine grained structures with fine dispersions of intermetallic compounds are observed in all extruded PM materials. The highest tensile strength of 483 MPa was obtained in Mg-5mass%Ca-5mass%Zn PM material with 2% tensile elongation. The tensile strength decreases and elongation increases significantly with rising test temperature. At elevated temperatures. A PM material of Mg-Ca binary alloys shows lower tensile strength than alloys with ternary additions. Nearly superplastic elongation of 200% is observed in Mg-5mass%Ca-5mass%Zn PM materials at 573 K.