Microstructural evolution and mechanical behaviour of LM13-ZrO₂ nanocomposites fabricated by bottom pouring stir casting

A sustainable manufacturing route in the form of resource-efficient bottom pouring stir casting process which minimizes material wastage, was used to create Nano Metal Matrix Composites (NMMCs) of aluminum alloy LM13 reinforced with nano-sized zirconium oxide (ZrO₂) particles. At different weight percentages (2.5–12.5 wt%), nano-ZrO₂ particles with an average size of 80 nm were added to the LM13 matrix. While EDS shows the existence of ZrO₂ in the composite, optical microscopy and SEM microstructural investigations verified homogeneous particle dispersion, good interfacial bonding, and low porosity. Although experimental values show somewhat lower because to casting porosity, both theoretical and experimental densities increases with reinforcement content. The hardness, ultimate tensile strength, and yield strength gradually increase as the ZrO₂ content rises from 2.5 to 10 wt%; however, a minor decline is noted at 12.5 wt% as a result of particle aggregation and microstructural flaws. As ZrO₂ addition increases, the percentage elongation continuously declines, suggesting decreased ductility. The addition of ZrO₂ greatly improved mechanical characteristics, with ultimate tensile strength peaking at 240.5 MPa at 10 wt% reinforcement and micro-vickers hardness reaching 133.3 HV (∼39% improvement) due to dispersion strengthening and grain refinement. Additionally, yield strength increased by about 34% (138.6 MPa). However, at 12.5 wt% ZrO₂, minor strength decreases were noted, which were ascribed to microstructural flaws and particle agglomeration. As reinforcement increased, fractography showed a shift from ductile to brittle fracture, which was correlated with decreased ductility. Overall, the study shows that the strength and wear resistance of the composite can be efficiently tailored by optimizing the nano-ZrO₂ content in LM13 alloy, creating a lightweight composite design which offers potential for reducing carbon emissions in automotive, aerospace and allied industrial applications.