Achieving synergistic strength-ductility optimization in ultralight Mg-11Li alloy by ultrahigh pressure treatment

Abstract

Magnesium‑lithium (Mg-Li) alloys with high content of Li element possess the body-centered cubic (BCC) matrix structure, exhibiting low density, excellent ductility but inferior strength. By traditional strengthening methods such as grain boundaries strengthening and precipitation strengthening, BCC Mg-Li alloys can remarkably enhance the strength while the ductility is substantially sacrificed. Here a superior strength-ductility synergy is achieved in Mg-11 % wt. Li alloys by ultrahigh pressure (UHP) treatment. The yield strength the sample treated at 1400 °C under 6 GPa can reach 280 MPa, which is 3.0 times higher than the original counterpart. Moreover, and uniform ductility of UHPed sample can remain 34 %, showing only 1 % loss compared with the original sample. This UHPed sample is stronger and more ductile than those Mg-Li based alloys reported so far. The BCC matrix structure in the original sample is transformed to the hexagonal close-packed (HCP) based structure due to the solute redistribution of Mg and Li elements during solidification under UHP. Moreover, dense {10−11} contraction nanotwins projected under rare [01−11] zone axis and coherent Li-segregated nanoparticles are formed in HCP α-Mg matrix. The interaction of {10–11} contraction nanotwins (twin dislocation) and Li-segregated nanoparticles (changed stacking structures) with the dislocations leads to the superior strength-ductility synergy in the UHPed sample. The findings in this work contribute to a deeper understanding of microstructure evolution and strengthening mechanisms in Mg-Li alloys and provide valuable insights for strength-ductility optimization of ultralight metallic materials.