The Structure of β″ and β′ in an Aged Mg-Nd Alloy

Abstract

The structures of the β″ and β′ phases in a Mg-2.35 wt. % Nd alloy aged at 250°C for 3 min, 15 min and 2 hr were investigated using high-angle annular dark field scanning transmission electron microscopy. Both phases consist of different arrangements of Nd atoms including triangular structures and hexagonal rings. In the [0001]_Mg orientation, some β′ precipitates also exhibit unexpected D0₁₉ stacking, which is explained by a projection artifact of stacking defects visible in the <11–20>_Mg zone axes. The β′ phase appears to nucleate from preexisting ß” chains. The β′ phase is coherent and contains the highest strain along the <11–20>_Mg directions, which agrees with the morphology of the precipitates being thinnest along the <11–20>_Mg directions.