<p>Complex concentrated alloys (CCAs) containing the L2₁ phase are recognized for their exceptional strength and thermal stability, positioning them as strong candidates for transformative applications in aerospace, energy, and structural sectors. This investigation delves into the AlFe_<i>x</i>NiTiV_{40−<i>x</i>} (<i>x</i> = 0, 10, 20, 30, 35, 40; at%) CCAs, aiming to unlock the synergistic potential of BCC and L2₁ phases. By conducting an in-depth analysis of microstructure, phase behavior, and mechanical properties, the intricate relationships between chemistry, structure, and properties are illuminated within this alloy system. The Al₁₅Fe₃₅Ni₃₀Ti₁₅V₅ alloy demonstrates remarkable mechanical properties, achieving a yield strength of 2140.9&#xa0;MPa and ultimate compressive strength of 2699.7&#xa0;MPa, primarily through solid solution strengthening and precipitation hardening. Notably, its low lattice mismatches and nanoprecipitate strengthening yield an impressive specific yield strength at 600 °C (245.2&#xa0;MPa(g·cm⁻³)⁻¹). Phase modulation achieves the synergistic optimization of specific strengths at both room and high temperatures in CCAs containing the L2₁ phase, opening new avenues for designing advanced lightweight and high strength alloys for elevated-temperature applications.</p> Graphical abstract <p></p>