Quasicrystalline-to-crystalline transformation in rapidly solidified Mg₃₂(Al, Zn)₄₉

Abstract

A ternary Mg-Al-Zn alloy, corresponding to the Mg₃₂(Al, Zn)₄₉ composition, was rapidly solidified from the liquid state by melt spinning. The as-solidified structure showed nodular morphology of the grains with a fine needle-like internal structure. The fivefold, threefold and twofold diffraction patterns unambiguously confirmed it to be the icosahedral phase. The quasilattice constant was calculated to be 0•518 nm. Fine structure of the diffraction patterns was inferred in terms of phason strains present in the quasilattice.

The formation of fine pores has been observed during transformation of the quasicrystalline to the crystalline phase. This has been explained by differences in density between the quasicrystalline and crystalline states and also by the faster diffusivity of one of the components (the Kirkendall effect). The crystal structure of the equilibrium phase has been shown to be b.c.c. with a= 1•422nm.