Designing new low alloyed Mg–RE alloys with high strength and ductility via high-speed extrusion

Two new low-alloyed Mg–2RE–0.8Mn–0.6Ca–0.5Zn (wt%, RE = Sm or Y) alloys are developed, which can be produced on an industrial scale via relatively high-speed extrusion. These two alloys are not only comparable to commercial AZ31 alloy in extrudability, but also have superior mechanical properties, especially in terms of yield strength (YS). The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys. The high strength–ductility mainly comes from the formation of fine grains, nano-spaced submicron/nano precipitates, and weak texture. Moreover, it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C, significantly higher than that of AZ31 alloy (YS: 45 MPa). The Zn/Ca solute segregation at grain boundaries, the improved heat resistance of matrix due to addition of RE, and the high melting points of strengthening particles (Mn, MgZn₂, and Mg–Zn–RE/Mg–Zn–RE–Ca) are mainly responsible for the excellent high-temperature strength.