Dual-scale (nano and micron) particle-reinforced TiB₂/6061Al matrix composites with different contents of TiB₂ were prepared using powder metallurgy, and then analyzed via microstructure observation and tests of microhardness, tensile properties, and friction and wear properties. The 6061Al powders’ particles changed from spherical to flaky after two rounds of high-energy ball milling, and the TiB₂ enhancer was embedded in or wrapped by the matrix particles after high-energy ball milling. Metallurgical bonding between TiB₂ particles and the matrix was achieved, and Al₃Ti was synthesized in situ during sintering. The hot-pressing process eliminated the internal defects of the composites, and the TiB₂ particles were diffusely distributed in the matrix. The best comprehensive mechanical properties (hardness and tensile strength) were achieved when the mass fraction of TiB₂ was 5% (1% micron + 4% nano); the hardness and tensile strength of the composites reached 131 HV and 221 MPa—79.5% and 93.9% higher than those of the pure matrix, respectively. The composites’ average coefficient of friction and volumetric wear rate were reduced. Composites with a TiB₂ mass fraction of 7% (3% micron + 4% nano) had the highest average coefficients of friction and the lowest volumetric wear rate of 0.402 and 0.216 mm³∙N⁻¹∙m⁻¹, respectively. It was observed that adhesion influences the friction mechanism, which transitions from adhesive wear with slight oxidative wear to abrasive wear.

Carbonation technology offers a novel approach to enhance steel slag performance, where the compaction degree plays a pivotal role in optimizing the carbonation process. This study reveals that as the compaction degree increases, the peak temperature in the carbonation environment gradually decreases, and the intensity of the carbonation reaction weakens. Post-carbonating, the compressive strength initially increases before declining, peaking at a compaction degree of 60%. At this optimal compaction degree, the material achieves a compressive strength of 124.4 MPa and a CO₂ uptake of 14.5%. The analysis of pore size distribution and carbonation products reveals that steel slag compacts with lower compaction degrees exhibit larger internal pores, leading to dispersed and isolated carbonation products, which restrict performance improvement. Conversely, excessively high compaction degrees cause the premature blockage of gas diffusion pathways by calcium carbonate particles, which impede the carbonation process and degrade the mechanical performance. The moderate compaction of steel slag effectively prevents the early blockage of gas channels, and significantly facilitates the accumulation and bonding of carbonation products, thereby achieving the superior performance.