AbstractThe newly developed Mg–Y–Sn extrusions are prepared by adding Sn (0.6 and 1.5 wt%) to Mg–6Y. The optimized Mg–6Y-1.5Sn exhibited superior elevated-temperature strength up to 300 °C, charactered by the pronounced strain hardening. Specifically, the yield stress and ultimate tensile strength of this alloy at 300 °C are 186 ± 3 MPa and 328 ± 7 MPa, respectively, which are 64% and 93% higher than that of the highly RE-alloyed WE54. Sn addition to Mg–6Y introduces a large number of thermal-stable micron/nano-scale Sn3Y5 precipitates. Mg–6Y-1.5Sn, which contained more nano-scale precipitates, exhibited better elevated-temperature strength than that of Mg–6Y-0.6Sn. The grain structure transitioned from a uniformed equiaxial grain in Mg–6Y to a thermal-stable multiscale grain structure in Mg–6Y-0.6/1.5Sn, which consisted of fiber textured un-DRXed area with high dislocation density and randomly orientated DRXed grains with low dislocation density. The exceptional elevated-temperature strength strongly correlated to the combined thermal-stable multiscale precipitates and grain structures.