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 Mg 5 RE (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 [0 (1) over bar1](w)//[(2) over bar 30](Mg12RE), and ((1) over bar 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 unrecrystallized 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. (C) 2018 Elsevier B.V. All rights reserved.