Precipitates in a Mg–Zn–Y alloy reinforced by an icosahedral quasicrystalline phase

The precipitation behavior under various heat treatment conditions in the as-cast and hot-rolled Mg–Zn–Y alloy has been investigated. While MgZn2 precipitates are distributed in the α-Mg matrix at 190 °C, in the temperature range of 350–420 °C, polygon-shaped icosahedral phase (I-phase) precipitates are mainly formed. The precipitated I-phase is mostly found to be localized near the eutectic region in the as-cast ingot, but it is randomly distributed throughout the refined α-Mg grains formed by dynamic recrystallization during the hot-rolling processes in the sheet. The I-phase precipitates have no specific orientation relationship with the α-Mg matrix and do not coarsen at high temperatures. An increase of the hardness value by I-phase precipitates is less significant than that by MgZn2 precipitates due to their relatively low number density and near-spherical morphology.