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 °C is identified to be SSSS → clusters/G.P. Zones → β ′ (Mg 7 Y) → β ′′/ β t ′′ (Mg 3 Y). A novel β t ′′ phase forms through in-situ transformation from the β ′ phase, which shares the same Mg 3 Y composition with D0 19 - β ′′ phase and exhibits the same cbco -structure as β ′ phase in Mg-Y based alloys. [Display omitted] • A new precipitation sequence, SSSS → clusters/G.P. Zones → β ′ (Mg 7 Y) → β ′′/ β t ′′ (Mg 3 Y), is observed in Mg-Y based alloys. • The β t ′′ phase, which has a Mg 3 Y composition and a cbco structure, is in-situ transformed from the β ′ phase. • The β t ′′ phase is stable after long-time exposure at elevated temperature. [ABSTRACT FROM AUTHOR]