<p>Al_<i>x</i>CoCrFeNi (<i>x</i> = 0.3, 0.6, 0.9) high-entropy alloys (HEAs) were synthesized via spark plasma sintering (SPS) to investigate the influence of Al content on phase evolution, mechanical properties, and wear behavior. As Al content increased, a distinct phase transformation occurred, transitioning from a single-phase face-centered cubic (FCC) structure at <i>x</i> = 0.3 to a dual-phase FCC and body-centered cubic (BCC) mixture at <i>x</i> = 0.6, and ultimately to a BCC-dominated structure at <i>x</i> = 0.9. This phase evolution was accompanied by a substantial increase in hardness, from 206 ± 6 HV to 578 ± 8 HV, and a notable enhancement in wear resistance, with wear rates decreasing from 7.2 ± 0.4 × 10⁻⁵ mm³ N⁻¹ m⁻¹ to 1.3 ± 0.1 × 10⁻⁵ mm³ N⁻¹ m⁻¹. The wear mechanism shifted from predominantly adhesive wear to a combination of adhesive and abrasive wear as the Al content increased. Fractographic analysis revealed a transition in fracture mode from ductile fracture with large dimples at <i>x</i> = 0.3, to quasi-cleavage fracture with shallow dimples and cleavage facets at <i>x</i> = 0.9. The tensile strength reached a peak of 829 MPa at <i>x</i> = 0.6, accompanied by a moderate elongation of 49%, due to the synergistic effects of the FCC and BCC phases. However, further increases in Al content led to excessive BCC phase formation and brittle fracture, which degraded tensile properties. These findings highlight the crucial role of Al in tailoring phase composition and achieving an optimal balance between strength, ductility, and wear resistance in HEAs.</p>