Although the strengthening and grain refinement effects of TiB2 particles on aluminum alloys have been extensively studied, their influence on casting behavior remains relatively underexplored. In this study, the influence of different addition amounts of submicron TiB2 particles on the microstructure, casting performance, and mechanical properties of an Al-Cu (ZL205A) alloy was systematically investigated. The introduction of TiB2 particles leads to significant grain refinement, transforming the microstructure from coarse grains to fine equiaxed grains by providing additional nucleation sites and inhibiting grain growth. SEM and TEM analyses reveal that the added submicron TiB2 particles exhibit minimal effect on the distribution of intermetallic phases or precipitates. Casting performance, as evaluated by spiral fluidity and hot tearing tests, shows notable improvements with TiB2 additions. At a TiB2 content of 3wt.%, the fluidity length increases by 20%, and the hot tearing susceptibility coefficient decreases by 29%. These enhancements are mainly due to the refined grain structure and the formation of interdendritic bridging in TiB2-reinforced alloys. However, the overall enahncement in casting properties shows little variation across the TiB2 additions from 0.2wt.% to 3wt.%. Mechanical testing shows that the highest hardness and strength are achieved with a 1wt.% addition of TiB2 particles, primarily attributed to refined grain size and reinforcement of the aluminum matrix. Based on these findings, a TiB2 particle content of 1wt.% is recommended for optimizing both the casting performance and mechanical properties of the ZL205A alloy.