Impact of Zirconium Inclusion on Microstructure and Mechanical Performance of Stir Cast AA6061 Reinforced with B₄C and SiC Hybrid Particles

Abstract The investigation is reported on the processing of AA6061 Hybrid Metal Matrix Composites (AHMMCs) with B4C, SiC, and Zr as reinforcing particles by the stir casting method. The AA6061 alloy was selected as the matrix material due to its excellent balance of strength, corrosion resistance, weldability and light weight, and the B4C and SiC ceramic reinforcements were added to improve the mechanical properties. The effect of the addition of Zr3, 5, 7, and 9 wt.% on the microstructure, ultimate tensile strength (UTS) and hardness of hybrid composites has been studied systematically. SEM analysis along with EDS graph verified the presence and even distribution of reinforcement particles in the AA6061 matrix. The microstructural study revealed better particle dispersion and a stronger matrix/reinforcement interface with the increase of Zr content. The mechanical results revealed an ever-increasing improvement in the strength and hardness as the Zr content increased. The composite containing 9 wt. % Zr yielded the maximum UTS of 246.47 MPa and hardness of 55.58 BHN, which were significantly higher with reference to lower Zr-added composites. The improvement in mechanical properties was attributed to the combined effects of ceramic reinforcement strengthening, grain refinement, enhanced load transfer efficiency, dislocation strengthening, and restricted plastic deformation. The hybrid reinforcement approach provided synergistic strengthening by combining the high hardness of B 4 C, the stiffness contribution of SiC, and the grain-refinement ability of Zr. The developed AA6061 + B₄C + SiC+Zr hybrid composite exhibits promising potential for lightweight structural applications requiring enhanced strength and hardness.