Creep behaviors of a Mg–Li based alloy at elevated temperatures

Improvement of the mechanical stability is a long challenge for the light and strong dual-phases MA21 (Mg-7.99Li-5.3Cd-4.57Al, wt.%) alloy with critical applications in aerospace and automotive industries. The present work experimentally investigated the relationship between the creep behaviors and microstructures of MA21 alloy at elevated temperatures. It was revealed that plate-like θ-phase precipitated in the α-phase and AlLi phase particles grew in the β-phase. These precipitate phase impeded the dislocation dynamics giving rise to the creep deformation. At low temperature and high stress, the creep behavior was dominated by dislocation climb accompanying Li atom diffusion, where the θ-phase was shear deformed. The AlLi particles were so hard to be penetrated by dislocation, so the dislocation slip can only propagate bypass it. In contrast, extensive atom diffusion of Al and Cd elements was revealed to support the dislocation slip mechanism with solute drag for the creep behaviors at high temperature and low stresses. The dislocation slip during creep resulted in grain reorientation with enhanced (0001) plane texture and transformation of large angle grain boundaries in the initial state into small angle grain boundaries. Our results shed new light on understanding of the time dependent deteriorated mechanical properties of Mg–Li commercial alloys and might give rise to a new strategy to stabilize the mechanical properties of MA21 alloy and relevant Mg–Li alloy system by engineering the precipitation phase in the α-Mg and β-Li phases.