Solidification microstructure of as-cast Mg-Zn-Y alloys

Composites consisting of icosahedral (i) phase and ductile α-Mg can be fabricated by controlling the alloy composition. With increasing Mg content, the primary solidification phase changed from the i phase to the α-Mg phase and single eutectic structure can be obtained at a composition of Mg ₇₂Zn_23.5Y_3.5. The i phase showed a variation in structural order from the well-ordered icosahedral phase to the 1/1 rhombohedral approximant with lattice constants a = 27.2 Å and α = 63.43°. The structural change in the i phase can be explained by microdomain formation due to compositional change during solidification. Annealing treatment improves the structural order of the i phase by homogenization. By controlling the alloy composition, a single eutectic structure consisting of a hard i phase and a ductile α-Mg phase could be obtained.