Effect Of Fly Ash Content on Microstructure and Mechanical Properties of Aluminium Matrix Composite Processed by Cooling Slope Casting

Metal matrix composites (MMCs) have emerged as promising materials for aerospace and automotive applications due to their enhanced mechanical performance. Among various reinforcements, fly ash has gained increasing attention for aluminium-based MMCs because of its low cost, low density, and favourable mechanical characteristics. However, the influence of fly ash content on the microstructural evolution and mechanical behaviour of aluminium MMCs fabricated via cooling slope casting remains insufficiently explored. In this study, aluminium MMCs reinforced with 4, 8, and 12 wt.% fly ash were produced using cooling slope casting under different pouring temperatures and slope lengths, followed by T6 heat treatment. Mechanical properties were evaluated through tensile and hardness testing, while microstructural characterization was performed using optical microscopy, FESEM with EDX, and XRD analysis. Quantitative image analysis was employed to determine the globule size and shape factor of the primary α-Al phase. The results demonstrate that increasing fly ash content promotes grain refinement, reduces globule size, and enhances globularity, indicating improved microstructural stability after heat treatment. These microstructural improvements, together with precipitation hardening and more effective load transfer, lead to significant mechanical strengthening, with yield strength, ultimate tensile strength, and hardness increasing by 43%, 25%, and 29%, , while elongation is maintained with a modest improvement of approximately 4%. Furthermore, the lower density of fly ash contributes to overall weight reduction, making these composites attractive for lightweight structural applications. The findings highlight the potential of fly ash-reinforced aluminium MMCs as cost-effective, high-performance materials for engineering applications.