Elucidation of formation and transformation mechanisms of Ca-rich Laves phase in Mg-Al-Ca-Mn alloys

The formation of thermally stable intermetallic phases plays a key role to enable high temperature appli-cations for Mg alloys. In the ductile Mg-Al-Ca system, Ca-rich Laves phases are expected to be crucial for improving high temperature mechanical properties. However, the formation mechanisms of Ca-rich Laves phases are still unresolved. Here, we report atomic-scale experiments and simulations on transformation of Ca-rich Laves phases and formation of Ca-rich clusters as well as Ca-segregation behaviour in Mg-Al-Ca-Mn alloys in three conditions: as-cast, homogenised (500 degrees C, 20 h), and rolled (350 degrees C). The formation me-chanisms of C36 Laves phase and Mg-rich particles (eutectic Mg) within C36 Laves phase were attributed to a divorced eutectic reaction. The transformation mechanisms from C36 to C15 Laves phase were revealed and discussed in terms of Mg out-diffusion of C36 Laves phase, the partitioning of Al into C36 Laves phase and the change of stacking sequences. The combined atomic-scale experimental and simulation in-vestigation reveals complex interactions among various Ca-rich Laves phases in Mg-Al-Ca-Mn alloys.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).