Mechanical and microstructural investigation of aluminum composites reinforced with boron carbide and zirconium

The current study investigates how the addition of zirconium (Zr) influences the mechanical and microstructural properties of composites consisting of aluminum and boron carbide (Al–B₄C) produced by powder metallurgy. To fabricate hybrid composites with improved mechanical properties, Al powder was reinforced with 7 wt% B₄C and additions of Zr in the range of 1–5 wt%. To achieve a uniform metallurgical bonding, the mixed powders were compacted and sintered for 2 h at 600 °C under an argon atmosphere. The influence exerted by Zr on impact energy, hardness, compressive strength, and densification has been investigated, and the results have been correlated to the microstructural features obtained using SEM. The results indicated that the addition of Zr significantly improved the densification and bonding characteristics between B₄C particles and the Al matrix. Indeed, porosity decreased from 2.5% (Al–7% B₄C) to 1.9% (Al– 7% B₄C–4% Zr), suggesting improved diffusion and wettability at the reinforcement–matrix interface. Grain refinement and dispersion strengthening were promoted by the formation of fine Al3Zr dispersoids, which favored a gradual enhancement of the mechanical properties. For 4 wt% Zr, Vickers hardness and compressive strength reached maximum values of 102 VHN and 285 MPa, respectively, and the impact energy also improved with 6.8 J, showing a good compromise between toughness and strength. Particle agglomeration and development of pores were held responsible for the slight deterioration of properties beyond 4 wt% Zr.