Microstructure and strengthening mechanism of hot-extruded ultralight Mg-Li-Al-Sn alloys with high strength

Duplex-structured Mg-7Li-2Al-1.5Sn alloys with high strength were fabricated and their strengthening mechanism was investigated. The Mg-7Li-2Al-1.5Sn alloys were prepared by casting and extruded at the temperature of 533 K with an extrusion ratio of 25:1. The microstructure and mechanical properties of Mg-7Li-2Al-1.5Sn alloys were systematically investigated by OM, XRD, SEM, TEM, and tensile tests. The results show that Mg-7Li-2Al-1.5Sn alloys are mainly composed of alpha-Mg, beta-Li, LiMgAl2, Mg2Sn and Li2MgSn phases. The yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of the extruded alloy at room temperature reach 250 MPa, 324 MPa and 11.9%, respectively. A lot of Sn-rich precipitates (Mg2Sn and Li2MgSn) are precipitated during extrusion with an average size of similar to 14 nm, which is beneficial to the grain refinement. Dynamic recrystallization occurs during hot deformation and the nanoprecipitates effectively refine the dynamic recrystallized (DRXed) grains. Besides, the residual dislocations existed in DRXed and un-DRXed grains result in the dislocation strengthening in the extruded alloy. Mg-7Li-2Al-1.5Sn alloys possess excellent high-temperature mechanical properties with the YS, UTS and EL of 200 MPa, 237 MPa and 26.7% at 423 K, respectively. Sn-rich precipitates with good thermal stability can effectively prevent grain growth, which is good for the improvement of the high-temperature performance of Mg-Li-Al-Sn alloy. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Duplex-structured Mg-7Li-2Al-1.5Sn alloys with high strength were fabricated and their strengthening mechanism was investigated. The alloys exhibited excellent high-temperature mechanical properties due to the presence of Sn-rich precipitates that prevent grain growth effectively.