The Effect of Bismuth and Tin on Mechanical and Tribological Performance of Compocast Aluminum Hybrid Composites Reinforced with Al₂O₃, ZrO₂, and SiC

The distribution of ceramic particles in the matrix plays a crucial role in enhancing the properties of aluminum matrix composites, especially wear resistance. In the current study, 0.5 wt% Bi and 0.5 wt% Sn were added separately to the Al-7Si-Mg matrix metal, followed by an introduction of Al₂O₃, ZrO_2, and SiC particles using the compocasting route at 605 ± 5 °C while the solid fraction of matrix alloy was 20%. Field emission scanning electron microscopy, EDS analysis, and XRD results confirmed that the ceramic particles were successfully incorporated into the matrix. However, microstructural examination of the cast composites shows that non-uniform particle distribution was obtained and that it varies between the top to bottom of the Al-7Si/Al₂O₃ + ZrO₂ composite. Additions of Bi and Sn produced a better and more uniform distribution of Al₂O₃, ZrO₂, and SiC particles within the matrix. Elemental mapping confirmed that Bi is segregated into the eutectic Al-Si area at the particle/matrix interface. Tribological testing conducted under applied loads of 5, 10, and 20 N identified the minimum specific wear rate and friction coefficient obtained in the Al-7Si + Bi/ZrO₂ + Al₂O₃ + SiC composite treated with Bi, which exhibited the highest hardness (75 BHN), YS (122.2 MPa), and UTS (153.1 MPa). Obtained results revealed a transition from adhesive to a combined adhesive and abrasive wear mechanism, suggesting enhanced wear resistance. Three scenarios can be essential factors that lead to better distribution of particles and superior properties of hybrid composite: (i) Bi reduces the surface tension of the matrix and facilitates the incorporation of ceramic particles into the matrix alloy, (ii) Bi mitigates the discontinuity and improves bonding strength at the matrix/particle interface, and (iii) Bi may play a role as solid lubricant under wear conditions.