Achieving high strength-ductility in a wrought Mg–9Gd–3Y–0.5Zr alloy by modifying with minor La addition

Abstract Effects of 0.5 wt% La addition on microstructures and mechanical properties of a traditional hot-extruded Mg–9Gd–3Y–0.5Zr alloy were thoroughly investigated in this work. The results indicate that minor La addition obviously improves the alloy’s mechanical performance at room temperature, accomplished an ultra-high tensile yield strength of 480 MPa with the elongation of ~6%, although leading to much lower high-temperature strength. Microstructural analysis reveals that after extrusion, minor La addition leads to a significantly higher level of recrystallization (the volume fraction is improved from 21% to 68%), much finer dynamically recrystallized (DRXed) grains (the average sizes are refined from 4.12 µm to 3.26 µm), and also finer non-recrystallization stripes. La addition promoting recrystallization is mainly attributed to the finer grains and much more intermetallics not only at grain boundaries but also in α-Mg grains of the ingots before extrusion. During peak-aging, minor La addition does not change intermetallics/precipitates in both DRXed grains and non-recrystallized regions except some extra coarse Mg17La2 particles mainly in extrusion stringers. Therefore, minor La addition improving both strength and ductility of the hot-extruded Mg–9Gd–3Y–0.5Zr alloy at room temperature is mainly by grain-refinement strengthening which is also the underlying cause for the lower work hardening coefficient, high-temperature strength but higher ductility.