Refractory high entropy alloys are strong candidates for high-temperature structural materials, because of their high strength, excellent thermal stability and exceptional softening resistance under high-temperature. However, majority of the existing refractory high entropy alloys are seriously limited in widespread application, due to their severe brittleness at room temperature. In this study, we proposed a novel AlxHfTaTi body-centered cubic (BCC) refractory medium entropy alloy with remarkable strength-ductility combination at room temperature. Adjusting the atomic ratio of Al (from 0 to 0.5 at.%), we investigated the effect of Al on the structure-property characteristics of the alloy under as-cast as well as cold-rolled and annealed conditions. Compared with the as-cast samples, the rolled and annealed samples exhibit more excellent tensile properties due to the remarkable reduction of grain size resulted from recrystallization. The Al0.3HfTaTi sample annealed for 5 min exhibits outstanding comprehensive properties at room temperature, with a yield strength higher than 1000 MPa and a fracture elongation of up to 24 ± 1 %, respectively. Quasi in-situ EBSD analysis results reveal that, during tensile deformation, the grain size has a significant effect on the grain rotation and dislocation gliding. Small grains are more likely to initiate multiple slip bands, promoting the synergistic effect of grain rotation and dislocation gliding, thereby improving the ductility of the alloy. Our findings can provide new ideas for the development of refractory high entropy alloys with outstanding room-temperature tensile properties.

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