Precipitation processes during the peak-aged and over-aged stages in an Mg-Gd-Y-Zr alloy

The precipitation processes during the peak-aged and over-aged stages of the as-extruded Mg-11.9Gd-1Y-0.44Zr (wt.%) alloy were investigated in detail by transmission electron microscopy. We revealed that, in addition to the dominant precipitate beta ', both beta(T) and beta(F)' precipitates were also found from the peak-aged stage. The transformation from bT to bF' gives rise to the formation of neck morphology that connects different beta-phases. The lengthening rate of precipitate in the <10<(1)over bar>0>(alpha) is larger than the thickening rate in the <1<(2)over bar>10>(alpha). In the over-aged condition, self-stress orienting phenomenon leads to the reduction of the variants of precipitates. The age-hardening of this alloy strongly depends on the formation of the size of the near-continuous network composed of the {11 (2) over bar0}(alpha) prismatic precipitates. The near-continuous precipitate network was formed in the peak-aged condition while the breakdown of the near-continuous precipitate network results in the significant decrease of hardness. (C) 2019 Elsevier B.V. All rights reserved.