Structures and mechanical properties of rapidly solidified Mg-Y based alloys

Mg-Y based alloys with or without ternary additions of Ca and Zn were rapidly solidified and consolidated into P/M materials by hot extrusion. Ternary alloying additions were 3 ma.% Ca for the Mg-5ma.%Y alloy and 2 ma.% Zn for the Mg-10ma.%Y alloy. Consolidation of the flakes was carried out by cold pressing and hot extrusion. In as rapidly solidified flakes of the Mg-Y binary alloys, extended solid solution of Y was obtained in the Mg matrix. But, fine lamellar structures, the spacing of which was approximately 400 nm, were observed in rapidly solidified flakes of the ternary alloys. Rapidly solidified flakes containing 10 ma.% Y showed hardness increases after heating at 473 K presumably due to precipitation of metastable β″ phase. After consolidation, a fine dispersion of intermetallic compounds was observed in all extruded P/M materials. Those compounds consisted of Mg24Y5 in binary alloys, and Mg24Y5, Mg2Ca or Mg12YZn in the ternary alloys. As-extruded P/M materials of Mg-10ma.%Y and Mg-10ma.%Y-2ma.%Zn alloys showed no remarkable softening after annealing at 573 K. The Mg-10ma.%Y-2ma.%Zn alloy showed the highest tensile strength of 520 MPa at room temperature and 440 MPa at 473 K. However, the tensile strength of all the P/M materials dropped below 80 MPa at 573 K.