Microstructural Characterization and Mechanical Performance Enhancement of Al-Cr and Al-Cr-Ni Alloys

This study details the development and characterization of high-performance aluminum-based alloys, with a focus on elucidating the influence of chromium (Cr) and nickel (Ni) additions on the microstructure, mechanical properties, and adhesive wear performance of Al–Cr and Al–Cr–Ni systems. The alloys were synthesized via in-situ metallothermic reduction of Ni₂O₃ and Cr₂O₃ within a molten aluminum matrix. Comprehensive microstructural characterization employing scanning electron microscopy (SEM), light optical microscopy (LOM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) confirmed the in-situ formation of multiple intermetallic phases, including Al₃Ni, Cr, Al₇Cr, and Al₈Cr₅. Mechanical property evaluation demonstrated that Cr additions induced moderate enhancements in tensile strength and Brinell hardness; however, these were accompanied by microstructural segregation originating from the presence of coarse intermetallic compounds. The incorporation of Ni, by contrast, yielded a significant improvement in mechanical performance, elevating the tensile strength from 66.5 MPa to 85.4 MPa and the hardness from 38 HB to 43 HB. This pronounced enhancement is ascribed to the precipitation of finely dispersed Al₃Ni intermetallic phases, which facilitated microstructural refinement of the chromium-containing constituents and suppressed the formation of coarse Al₇Cr and Al₈Cr₅ phases. adhesive wear assessments further revealed a marked improvement in wear resistance for the ternary Al–Cr–Ni alloys, as quantified by a reduction in mass loss during pin-on-disk testing. This improvement is correlated with the formation of hard reinforcing intermetallics, notably Al₀.₉₈₃Cr₀.₀₁₇ and the σ–phase (Cr₇Ni₃), which contributed to simultaneous enhancements in mechanical strength.