Influence of Sm addition on microstructural and mechanical properties of as-extruded Mg–9Li–5Al alloy

Abstract

In this study, the influence of Sm addition on microstructural evolution and mechanical properties of as-extruded Mg–9Li–5Al (LA95) alloy was characterized by OM, SEM, TEM, XRD and EDS. The morphology results showed that adding Sm resulted in the formation of Al2Sm phase, and the grains of the LA95 alloy were markedly refined with the addition of Sm. Additionally, the dislocation pile-up around the Al2Sm particles were observed by high-resolution transmission electron microscopy. The as-extruded LA95-0.4Sm alloy with granular Al2Sm phase showed optimal ultimate tensile strength of 283 MPa, which was about 25% higher than that of the matrix alloy. The main factors influencing the strength of as-extruded LA95-xSm alloys were as follows: (i) grain refinement strengthening, the lattice mismatch calculation results showed that the average lattice mismatch of (111)Al2Sm//(0001)α-Mg was 12.5%, which indicated that the Al2Sm phase served as an effective heterogeneous nucleation substrate of the α-Mg phase to refine the α-Mg phase in LA95 alloys; (ii) second phase strengthening, the fine Al2Sm particles exerted positive effects on strengthening by effectively hindering the dislocation line movement, thereby forming the dislocation pile-up adjacent to the strengthening phase Al2Sm.