Solidification of Mg28Zn2Y and Icosahedral quasicrystal morphology evolution

Applying XRD, OM, SEM and TEM techniques, an investigation on the solidification of Mg28Zn2Y quasicrystal alloy was carried out. It is found that alpha-Mg phase, Mg7Zn3 phase and icosahedral quasicrystal phase coexist in the as-solidified morphology. A perfect five-branch icosahedral quasicrystal morphology was observed. It is attributed to the icosahedral quasicrystal free growth with preferred growth direction of five-fold symmetry axes resulting in five-branch morphology. Furthermore, the effect of cooling rate on the quasi-crystal morphology was also studied. High cooling rate leads to rapid solidification, and in turn, petal-like quasi-crystal morphology is reserved. On the other hand, slow cooling rate favors coarsening and branching of the quasi-crystal, and subsequently, subjected to long curing time, the formation of polygonal quasi-crystals driven by the action of interface energy.