Magnesium alloys have great potential as structural materials, since they are the lightest of all structural alloys used in industry. The icosahedral phase has a quasi-periodic structure, which is quite different from the crystalline phases. This phase possesses five fold symmetry and do not have the translational symmetry. In the case of the dispersed particle, this phase occurs in equilibrium with a matrix phase, showing a definite orientation relationship and with a strong interface, i.e., the formation of a coherent interface between the matrix and the particle. In the magnesium system alloys, the formation of the quasicrystal phase has been confirmed for the Mg-Zn-RE (RE = Y, Gd, Tb, Dy, Ho and Er) systems through various experiments, and this quasicrystal phase has been studied as the strengthening phase in magnesium alloys. The quasicrystal phase is dispersed as particles in the matrix by thermo-mechanical processes, such as rolling, extrusion and forging. These alloys exhibit high ductility and toughness with good strength at room temperature and a highly stable microstructure at elevated temperatures. To date, some kinds of Mg-Zn-RE alloys with dispersed the quasicrystal phase particle have been observed the superplastic behavior; however, the effect of interface between the matrix and the particle on the superplastic behavior has not been investigated. Therefore, in this study, the role of the dispersion of quasicrystal phase particle during the superplastic flow was examined using the Mg-Zn-Y alloy produced by extrusion. In addition, the possibility for the secondary forming, i.e., superplastic forging forming, was also performed in the same alloy.
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