The duration of ball milling greatly influences the characteristics of high-silicon–aluminum composite during the ball milling process. This study examines how the microstructure, thermal conductivity, and hardness of a high-silicon–aluminum composite are affected by different ball milling times. We exposed the powder to various durations of ball milling and employed different pellet ratios. Following this treatment, the powder underwent consolidation via discharge plasma sintering. Our findings show that with a pellet ratio of 10:1 and a milling duration of 8 h, the powder particles were refined, resulting in a more uniform and dense material composition. This refined material boasted a thermal conductivity of 111.6 W/m·K, a Brinell hardness of 136.8 HBW, and a density of 2.304 g/cm³. This method facilitates the creation of a uniform composite powder composition. It encourages the development of a fine-grain structure, which enables the production of particle-reinforced composites with superior properties.