Effect of Friction Stir Processing on Microstructure, Mechanical Properties and Texture Evolution of Dual-Phase Mg-Li Alloy

Abstract

In this study, the effects of friction stir processing on the microstructure and mechanical properties of the Mg-7.8Li-0.7Zn-0.4Sr-0.4Ca alloy were systematically evaluated, aiming to optimize this advanced solid-state processing technology for lightweight structural applications. The results demonstrate that friction stir processing effectively refines the stir zone microstructure by transforming elongated α-Mg and β-Li phases into equiaxed grains, resulting in a significant 32% improvement in tensile strength, reaching 210 MPa. In addition, the process exhibits a significant influence on the texture evolution of the two phases. At higher welding speeds, the α-Mg phase tends to form double-peak textures, while at lower welding speeds, its texture gradually transitions from double-peak to single-peak and ultimately to a random texture, effectively reducing mechanical anisotropy. Meanwhile, the texture strength of the β-Li phase is weakened, accompanied by the emergence of new texture components. Advanced characterization techniques, such as transmission electron microscopy, revealed a large number of nanoscale MgZn2 precipitates along grain boundaries, which enhance grain boundary strengthening and further improve mechanical performance. Importantly, a rare FCC-β-Li phase was observed in the processed sample. This discovery provides a practical framework for tailoring the relative content and spatial distribution of HCP-α-Mg, BCC-β-Li, and FCC-β-Li phases, offering a new pathway for achieving an optimal balance between strength and ductility in dual-phase Mg-Li alloys. These findings highlight the engineering potential of friction stir processing in producing high-performance Mg-Li alloys for lightweight and energy-efficient structural applications.

Keywords: Friction stir processing, Microstructure, Mechanical properties, Texture evolution, Phase transition