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

Abstract

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 β′, both βT and βF' precipitates were also found from the peak-aged stage. The transformation from βT to βF' gives rise to the formation of neck morphology that connects different β-phases. The lengthening rate of precipitate in the <101¯0>α is larger than the thickening rate in the <12¯10>α. 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 {112¯0}α 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.