High-Ductility Mg-9li-1zn-2gd-1.2mn Alloy Prepared Via Traditional Hot Extrusion

The dual-phase Mg-9Li-1Zn-2Gd-1.2Mn alloys were prepared by traditional hot extrusion at 200°C, 250°C, and 300°C, respectively. The microstructure of as-extruded Mg-9Li-1Zn-2Gd-1.2Mn alloy is remarkably refined, and the mechanical properties are significantly improved compared with the as-cast alloy. The Mg-9Li-1Zn-2Gd-1.2Mn alloy extruded at 200°C exhibits the best comprehensive mechanical properties among the alloys with the yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (εef) are 141 MPa, 166 MPa, and 57%, respectively. The dispersed second phases and Zn segregation along the grain boundary inhibit the growth of recrystallized grains and reduce the grain size, contributing to high ductility. Then, the unstable stacking fault energy of {0001}<110> slip system (γusf(basal)) and surface energy of {0001} plane (γs(basal)) in Mg and Mg-Li-Gd-Zn supercells are characterized by first-principles calculation. The results indicated that the value of γusf(basal) decreased from 259 mJ/m2 to 249 mJ/m2, while the value of γs(basal) increased from 537 mJ/m2 to 597 mJ/m2. The lower γusf(basal) promotes the initiation of basal slip and higher γs(basal) leads to a lower cracking tendency, revealing the ductility improvement by adding Li, Zn, and Gd elements. This work provides an effective strategy to prepare high-ductility Mg-Li alloys.