Developing a lamellar-structured Mg-4Li-3Al-0.4Ca alloy with high strength-ductility synergy

Abstract

The low strength of Mg-Li alloys sets a limit to lightweight applications. Introducing crystal defects (twins, dislocations, and SFs) is a distinctive strategy for maintaining good mechanical properties of metallic materials. A lamellar-structured Mg-4Li-3Al-0.4Ca alloy with high performance was prepared by hot extrusion and rotary swaging. The as-swaged alloy exhibits excellent mechanical properties with tensile strength, yield strength, elongation to failure, and specific strength of 391 MPa, 312 MPa, 14.2%, and 238.4 kN m kg⁻¹, respectively. The average grain size of the as-swaged alloy is 160 ± 23 nm, and the microstructure is mainly composed of lamellar structures, twins, ultrafine grains, and nano-grains. The abundant lamellar structures and twins promote the storage of dislocations and SFs, leading to the formation of twin-twin interactions and enhancing strain hardening. The formation of UFG and NG by dynamic recrystallization further improves the yield strength. Shearable second phases play a critical role in enhancing the yield strength and ductility. More importantly, extensive planar dislocation glide and <c+a> dislocations efficiently relax the local stress concentrations, and thus improve the ductility.