Effects of Sm addition on microstructure evolutions and mechanical properties of high-strength Mg–Gd−Sm–Zr extruded alloys

Abstract

Effects of various Sm additions on microstructures and mechanical properties of a hot-extruded Mg–14Gd−0.5Zr alloy were studied in this work. The results indicate that Sm addition firstly clearly improves the strength and then decrease as the Sm content increases at both room temperature and high temperatures. The highest yield strength was obtained to be ∼495 MPa and ∼512 MPa under tension and compression, respectively, at room temperature with the Sm concentration of 1 wt% while those were to be 384 MPa and 248 MPa at 250 °C and 300 °C, respectively, with the Sm content of 0.5 wt%. Electron backscatter diffraction mappings reveal that Sm addition significantly promotes dynamic recrystallization, resulted in much more fine recrystallized grains and lower texture intensity. Furthermore, transmission electron microscopy observations show that Sm addition increases dynamic precipitates particularly in non-recrystallized regions, leading to relatively less aging precipitates during artificial peak-aging. Finally, discussion based on grain boundary strengthening and dispersion strengthening suggests that Sm addition improving the yield strength of the extruded Mg–14Gd−0.5Zr alloy is mainly attributed to more grain boundaries and dynamic precipitates at room temperature and high temperatures, respectively.