Microstructure evolution and mechanical properties improvement of (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x lightweight high-entropy alloy by Laves phase transformation

(Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x (x = 0, 0.1, 0.2, 0.3, 0.4 at.%) lightweight high-entropy alloys with different contents of Al were prepared via vacuum non-consumable arc melting method. Effects of adding varying Al contents on phase constitution, microstructure characteristics and mechanical properties of the lightweight alloys were studied. Results show that Ti₈Zr₆Nb₄V₅Cr₄ alloy is composed of body-centered cubic (BCC) phase and C15 Laves phase, while (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x lightweight high-entropy alloys by addition of Al are composed of BCC phase and C14 Laves phase. Addition of Al into Ti₈Zr₆Nb₄V₅Cr₄ lightweight high-entropy alloy can transform C15 Laves phase to C14 Laves phase. With further addition of Al, BCC phase of alloys is significantly refined, and the volume fraction of C14 Laves phase is raised obviously. Meanwhile, the dimension of BCC phase in the alloy by addition of 0.3 at.% Al is the most refined and that of Laves phase is also obviously refined. Adding Al to Ti₈Zr₆Nb₄V₅Cr₄ alloy can not only reduce the density of (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x alloy, but also improve strength of (Ti₈Zr₆Nb₄V₅Cr₄)_100−xAl_x alloy. As Al content increased from 0 to 0.4 at.%, the density of the alloy decreased from 6.22 ± 0.875 to 5.79 ± 0.679 g cm⁻³. Moreover, compressive strength of the alloy by 0.3 at.% Al addition is the highest to 1996.9 MPa, while fracture strain of the alloy is 16.82%. Strength improvement of alloys mainly results from microstructure refinement and precipitation of C14 Laves by Al addition into Ti₈Zr₆Nb₄V₅Cr₄ lightweight high-entropy alloy.