Microstructures and mechanical properties of a hot-extruded Mg−8Gd−3Yb−1.2Zn−0.5Zr (wt%) alloy

Microstructures and mechanical properties of a Mg−8Gd−3Yb−1.2Zn−0.5Zr (wt%) alloy have been investigated. The dominant intermetallic phases in the as-cast sample are Mg5RE (RE = Gd,Yb) phase, 14H-type long-period stacking ordered (LPSO) phase, and Mg2Zn2RE (W) phase and ordered Mg12RE phase. Furthermore, the ordered Mg12RE phase generally coexists with the W phase following an orientation relationship as [01¯1]w//[2¯30]Mg12RE, and (1¯11)w//(001)Mg12RE. After extrusion, the microstructure is consisted of un-recrystallized regions along with a small part of fine dynamically recrystallized (DRXed) regions. Simultaneously, the coarse Mg5RE, W and Mg12RE particles were disintegrated and mainly distribute at extrusion stringers while the fine LPSO plates mainly distribute in un-recrystallized regions. Moreover, amounts of nanoscale Mg5RE particles were dynamically precipitated in DXRed regions. Then, the as-extruded Mg−8Gd−3Yb−1.2Zn−0.5Zr alloy exhibits clearly higher strength than the classic rare-earth-containing magnesium alloys with comparative or even much higher rare earth content at both room temperature and high temperatures. The dominant strengthening mechanism was finally revealed as precipitation/dispersion strengthening. •Microstructures and mechanical properties of a Mg−Gd−Yb−Zn−Zr alloy were studied.•Four dominant intermetallic phases namely Mg5RE, 14H LPSO, W, and Mg12RE, were found.•W always coexists with Mg12RE following [01¯1]w//[2¯30]Mg12RE, and (1¯11)w//(001)Mg12RE.•Amounts of nanoscale Mg5RE particles dynamically precipitated in the DRXed regions.•This alloy exhibits obviously high strength with UTS of 425 MPa and YS of 413 MPa.