Variable precipitation behaviors of Laves phases in an ultralight Mg-Li-Zn alloy

Abstract

Precipitation habits plays a decisive role in strengthening materials, especially for Mg alloys the non-basal plane precipitation is necessary but very limited. Generally, the precipitates would nucleate and grow up in a specific habit plane owing to the constraint of free-energy minimization of the system. Herein, in an aged ultralight Mg-Li-Zn alloy, we confirmed that the precipitates dominated by C15 Laves structure could form in a variety of habit planes, to generate three forms of strengthening-phases, i.e., precipitate-rod, precipitate-lath, and precipitate-plate. Among which, the precipitate-plates are on basal plane as usually but precipitate-rods/laths are on non-basal plane, and such non-basal precipitates would transform into the basal (Mg, Li)Zn2 Laves structure with prolonged aging. These findings are interesting to understand the precipitation behaviors of multi-domain Laves structures in hexagonal close-packed crystals, and expected to provide a guidance for designing ultralight high-strength Mg-Li based alloys via precipitation hardening on the non-basal planes.