Tuning texture and precipitation using Y/Gd atomic ratio in iso- concentration Mg-Y-Gd-Ag-Zr extruded alloys

Three Mg-Y(-Gd)-Ag-Zr alloys with an iso-concentration of total alloying elements but different Y/Gd atomic ratios were hot extruded at 350 degrees C and their microstructures and mechanical properties were comparatively studied. Extruded Mg-2.4Y-0.4Ag-0.1Zr (at%) base alloy shows a bimodal-grained structure composed of fine equiaxed recrystallised grains and coarse elongated unrecrystallised grains and has a < 01 (1) over bar0 >//ED (extrusion direction) texture. In contrast, when Y is partially replaced with Gd, extruded Mg-1.6Y-0.8Gd-0.4Ag-0.1Zr (at %) and Mg-0.8Y-1.6Gd-0.4Ag-0.1Zr (at%) alloys with the Y/Gd atomic ratio of 2 and 0.5, respectively, exhibit a near fully recrystallised structure and have a [0001]//ED texture. While basal gamma '' precipitates dominate but few beta' precipitates form in Mg-2.4Y-0.4Ag-0.1Zr alloy, a large number density of both beta' and gamma '' precipitates form in Mg-1.6Y-0.8Gd-0.4Ag-0.1Zr and Mg-0.8Y-1.6Gd-0.4Ag-0.1Zr alloys after post-extrusion ageing. Precipitation in the Gd-containing alloys is considerably enhanced by partial substituting Y with Gd. The peak-aged Mg-1.6Y-0.8Gd-0.4Ag-0.1Zr alloy keeps a relatively good balance between grain boundary strengthening, dispersion strengthening and precipitation hardening and thus obtains a good combination of strength and ductility, whose room temperature tensile yield strength, ultimate tensile strength and elongation are 377 MPa, 479 MPa and 8.0%, respectively.