This study addresses challenges in metal matrix composite fabrication by optimizing an ultrasonic-assisted stir casting process for aluminum LM25 composites reinforced with 5 wt% MoS2 and varying SiC nanoparticles (5–15 wt%). While previous research explored individual benefits of these reinforcements, their synergistic effects in hybrid composites remain underexplored. Our experimental investigation establishes correlations between processing parameters, microstructure, and mechanical properties. SEM-EDX mapping confirms uniform reinforcement dispersion with well-defined interfacial reaction zones (120–180 nm). Porosity decreases from 3.2% in the unreinforced alloy to 1.1% in the 15 wt% SiC composite. The LM25–5% MoS2–15% SiC composite demonstrates significant mechanical improvements: 34.23% higher ultimate tensile strength (312.64 MPa), 40.93% increased yield strength (220.56 MPa), and 40.57% greater hardness (118.24 BHN). These enhancements result from multiple strengthening mechanisms including Orowan strengthening, Hall-Petch effect (grain size reduction from 42 to 12 μm), and improved load transfer efficiency. Fractography reveals a transition from dimple-dominated ductile fracture in the base alloy to mixed-mode fracture with transgranular cleavage in reinforced composites. © 2025 Elsevier B.V., All rights reserved.