Microstructures and mechanical properties of as-extruded Mg–8Gd–2Y–1Zn–6Li alloy

Abstract

In this study, a high-performance Mg–8Gd–2Y–1Zn–6Li (wt%) alloy having a TYS of 202 ± 2.6 MPa, UTS of 243 ± 2.1 MPa and EL of 10.7 ± 2.3% was successfully fabricated by casting, heat treatment and hot extrusion. The effects of intermetallic compounds on microstructure and mechanical properties were deeply investigated. The results show that the studied alloy consists of coarse deformed α-Mg grains with (0001) basal texture, fine recrystallized β-Li grains with (002) texture and three Mg3RE phase variants, which are bulk Mg3RE phase with a size range of 10–30 µm, spot Mg3RE phase with a size range of 1–2 µm and spherical Mg3RE phase with a size range of 0.3–1 µm, respectively. The spherical Mg3RE phase has a strong dispersion strengthening effect, while the bulk Mg3RE phase acts as crack resources and deteriorates the ductility. A novel island-like β1R phase (FCC, a = 0.78 nm) is found for the first time in the Mg-Gd-Li based alloys. It has a coherent (1̅12)β1R//(101̅0)α interface at the broad facet and a semi-coherent (1̅11)β1R//(112̅0)α interface at the end facet. The β1R phase transforms from βH phase at the semi-coherent interface by atomic shear of RE and Mg atoms. The β1R phase provides a significant precipitation strengthening effect to the studied alloy, while the dissolution of β1R phase results in the age-softening phenomenon. The high-performance of the studied alloy is mainly attributed to the α/β duplex structure, three Mg3RE phase variants, and β1R phase.