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

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 alpha-Mg grains with (0001) basal texture, fine recrystallized beta-Li grains with (002) texture and three Mg3RE phase variants, which are bulk Mg3RE phase with a size range of 10-30 mu m, spot Mg3RE phase with a size range of 1-2 mu m and spherical Mg3RE phase with a size range of 0.3-1 mu m, 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 beta(1R) phase (FCC, a = 0.78 nm) is found for the first time in the Mg-Gd-Li based alloys. It has a coherent ((1) over bar 12)beta(1R//)(10 (1) over bar0)(alpha) interface at the broad facet and a semi-coherent ((1) over bar 11)beta(1R)//(11 (2) over bar0)alpha interface at the end facet. The beta(1R) phase transforms from beta(H) phase at the semi-coherent interface by atomic shear of RE and Mg atoms. The beta(1R) phase provides a significant precipitation strengthening effect to the studied alloy, while the dissolution of beta(1R )phase results in the age-softening phenomenon. The high-performance of the studied alloy is mainly attributed to the alpha/beta( )duplex structure, three Mg3RE phase variants, and beta(1R )phase. (C) 2021 Elsevier B.V. All rights reserved.