Ultrastrong and ductile BCC high-entropy alloys with low-density via dislocation regulation and nanoprecipitates

•Novel strong and tough (Zr0.5Ti0.35Nb0.15)100-xAlx alloys with BCC structure are designed.•Ultrahigh tensile strength comparable to that of amorphous materials is a record-high value known in BCCHEAs.•The brittleness and weak strain-hardening ability of BCC alloys are overcome by regulating dislocation mobility and inducing nanoprecipitates.•Relatively low densities of less than 6 g/cm3 are exhibited in these alloys.