Influence of TiB2 inclusion on the microstructural evolution and mechanical performance of stir-cast AA7075 composites

AA7075 aluminium alloy composites containing 0–20 wt% titanium diboride (TiB 2 ) fabricated via stir casting were assessed for density, mechanical properties, and microstructural features. The theoretical density augmented from 2.81 g/cm 3 for AMC0 (as-cast) to 3.04 g/cm 3 for AMC20 (20 wt% TiB 2 ) due to the TiB 2 supplement. Experimental density too increased with TiB 2 loading but persisted slightly lesser than theoretical values, showing the occurrence of casting-associated porosity, notably at higher reinforcement rates. Mechanical results showed that AMC15 (15 wt% TiB 2 ) exhibited the optimum performance, with tensile, yield, impact, compressive, and flexural strength, and hardness improved by approximately 69.47%, 78.33%, 25%, 72.99%, 117.77%, and 30%, respectively, compared with AMC0. The enhancement is associated to improved load transfer, restricted matrix deformation, grain refinement, dislocation strengthening, crack deflection, and increased resistance to plastic flow by hard TiB 2 particles. However, AMC20 showed reduced performance compared with AMC15, including decreases of about 37.79% and 38.21% in tensile and yield strength, 15.57% in hardness, 20% in impact strength, 22.21% in flexural strength, and 24.58% in compressive strength. In contrast to AMC15, which exhibited superior matrix compactness and fracture pathways as shown by SEM and fractography, AMC20 displayed characteristics such as pore development, particle-rich areas, and early crack-linking.