Unveiling precipitation behavior in Mg-Y based alloys

Mg-Y based alloys exhibit a promising combination of strength and deformability through tuning precipitation and solute strengthening mechanisms and tailoring the activity of non-basal dislocations. Understanding the precipitation sequence of Mg-Y based alloys and its dependence on Yttrium concentration in the matrix will provide a guideline for fine tuning structure, morphology and distribution of precipitates in Mg-Y based alloys. In this paper, we explore the precipitation behaviors of Mg-11Y (wt%) and Mg-11Y-1Al (wt%) alloys using aberration-corrected scanning transmission electron microscopy, and rationalize the experimental observations based on first-principles density functional theory calculations. The precipitation sequence during ageing at 225 degrees C is identified to be SSSS -> clusters/G.P. Zones ->beta' (Mg7Y) -> beta ''/beta(t)'' (Mg3Y). A novel beta(t)'' phase forms through in-situ transformation from the beta' phase, which shares the same Mg3Y composition with D0(19)-beta '' phase and exhibits the same cbco-structure as beta' phase in Mg-Y based alloys. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).