Strengthening Mechanisms and Thermal Stability of Mg-Li-Ca Alloys Processed by Severe Plastic Deformation

Magnesium-Lithium alloys have long been investigated for their potential to realize ultralightweight structural materials, however, efforts have been limited by a combination of low strength and thermal stability at low homologous temperatures. We report the implementation of severe plastic deformation (specifically, ambient temperature high-pressure torsion (HPT)) to refine the grain structures of Mg-3.5Li-0.6Ca (wt.%) alloy to the sub-micrometer regime via the imposition of hydrostatic pressure and strain at ambient temperatures. The grain refinement results in increased hardness and strength while deformation-induced Mg2Ca nanoprecipitates further strengthen the alloy and hinder grain boundary movement at elevated temperatures. Recrystallization curves as a function of strain applied during HPT with concurrent microstructural and hardness evolution are reported.