MECHANICAL AND MICROSTRUCTURAL BEHAVIOUR OF STIR-CAST AA7065–B4C–GRAPHITE HYBRID COMPOSITES WITH OPTIMIZED REINFORCEMENT CONTENT

High-strength aluminium hybrids reinforced with ceramics and solid lubricants are used in structural and tribological parts.
AA7065 supports precipitation hardening and the incorporation of B4C and graphite. Quantitative links between reinforcement
content and mechanical behaviour remain limited for AA7065. This study quantifies the effect of B4C content at a near-constant
graphite level on hardness, tensile metrics, and Izod impact energy. Hybrids containing 0–7 w/% B4C with 3 w/% graphite were
produced by vortex-assisted stir casting, T6-treated, machined into ASTM E8 and ASTM D256 specimens, tested, and characterized
using optical/SEM microscopy, followed by ANOVA response-surface analysis. Strengthening is evident, with hardness
increasing from about 100 HV to about 130 HV (30 %), and tensile strength increasing from about 300 MPa to about 360 MPa
(20 %) at 7 w/% B4C. Damage tolerance declined, with elongation decreasing from about 12 % to about 5 %, and Izod impact
energy decreasing from about 20 J to about 12 J. The pattern is consistent with load transfer and dislocation blocking combined
with particle-assisted void nucleation. These data guide reinforcement selection for AA7065–B4C–graphite composites used in
high-strength parts with controlled deformability. Future work will target fatigue and wear response under service loading and
evaluate graphite fraction and particle size as design variables.