Investigating the Effects of Adding Si3N4 on Microstructural and Mechanical Characteristics of AA7075-based TiB2-Reinforced Hybrid MMCs

The present study investigates the effects of a distinct specific combination of reinforcements silicon nitride (Si 3 N 4 ) and titanium diboride (TiB 2 ) on the microstructural and mechanical properties of hybrid MMCs containing Al-Zn-Mg alloy. The composites are fabricated by adding a fixed quantity of TiB 2 (2 wt%) and varying quantities of Si 3 N 4 (2, 4, 6, and 8 wt%) into AA7075 alloy using a two-step liquid state stir casting process. The physical and mechanical characteristics are investigated through the measurements of density, porosity, Brinell hardness, tensile, impact, and flexural strength of fabricated HMMCs. The microstructural analysis of HMMCs revealed a consistent distribution of ceramic reinforcement in the base alloy and significant fusion at the interface along with some instances of porosity. The presence of reinforcement particles is confirmed through FESEM with EDS and XRD analysis of HMMCs samples. It is observed that a composite containing 6 wt% Si 3 N 4 and 2 wt% TiB 2 particles exhibited the highest strength. It demonstrated a significant improvement of 67.67% in ultimate tensile strength, 54.53% in Brinell hardness, and 21.45% in flexural strength compared to the base alloy. However, it resulted in reduced ductility and impact strength as indicated by the decrease in percentage elongation and energy absorption capacity of HMMCs samples. It is concluded that the addition of Si 3 N 4 beyond 6 wt% led to several casting flaws, such as porosity, cluster, and agglomeration of reinforcement particles.