Influence of Si addition on the microstructure, mechanical, and wear properties of as-cast Al0.43CoCrFeNi2.1 high-entropy alloys and enhancement of properties via cold rolling and annealing treatment

The as-cast SiX=0,0.1,0.2,0.3Al0.43CoCrFeNi2.1 HEA were successfully fabricated through vacuum-assisted melting. A systematic investigation was conducted on the phase constituents, microstructural features, and mechanical response (including hardness, tensile behavior, and wear behavior) of the alloys with varying Si content. The results reveal that the addition of Si promotes the precipitation of a BCC1 phase enriched in Al, Ni, and Si with a B2-ordered structure. Furthermore, a secondary BCC2 phase enriched in Cr, Fe, and Si precipitates within the BCC1 matrix. Ultimately, a multiphase structure consisting of FCC/ (BCC1/BCC2) is formed. The microstructural evolution driven by Si addition significantly enhances the mechanical properties of the SiX=0,0.1,0.2,0.3Al0.43CoCrFeNi2.1 HEA. As Si content increases, both microhardness and tensile strength improve by approximately 42.1% and 54.9%, reaching 2.359 GPa and 785 MPa, respectively. The quantitative evaluation of the various strengthening mechanisms indicates that the intrinsic hardness of the FCC matrix, and the hardening due to the BCC1/BCC2 precipitation dominate the overall microhardness. The ΔHCS + ΔHMS < ΔH Orowan suggest the BCC2 primarily strengthens the alloy through a shear mechanism. Meanwhile, reduced friction and wear, together with smoother worn surfaces, reflect greatly enhanced wear resistance. Furthermore, after the optimal cold-rolling and annealing treatment (CR-800-1h), the Si0.3Al0.43CoCrFeNi2.1 alloy shows a 56% and 61% increase in microhardness and tensile strength, respectively, compared to the as-cast state, reaching 3.68 GPa and 1270 MPa. This enhancement is attributed to the synergistic effects of residual strain hardening FCC ordering, and L1₂/BCC precipitation strengthening