Development of castable aluminium A356-SiC metal matrix nanocomposites by addition of aluminium pellets reinforced by high concentration of SiC nanoparticles

Interest in aluminium metal matrix nanocomposites (MMNCs) has grown over the past four decades in the automotive and aerospace industries due to their superior strength, fracture toughness, creep resistance and wear resistance compared to conventional metal matrix composites (MMCs). Al-MMNCs also hold an advantage at higher temperatures due to their increased dimensional stability. However, there are major manufacturing difficulties due to poor wettability between ceramic nanoparticles and metal matrices, made worse by the high surface-to-volume ratio. These issues cause the nanoparticles to agglomerate, making uniform distribution the main challenge in MMNC fabrication. Whilst there are many successful manufacture techniques, they are inapplicable or unreliable for use in industry. In this study, aluminium A356 reinforced by 50nm silicon carbide particles are produced using stir casting and ultrasonic treatment with pre-milled green compact A356 and SiC nanoparticle-rich pellets. Although unfeasible for industrial scales, ultrasonic treatment is used to evaluate the potential of using pellets to cast MMNCs, serving as a first step towards industrial scale production of aluminium MMNCs. The A356-SiC pellets are well-mixed, aiding nanoparticle dispersion and offering an easy feeding technique. Using GAKTPore on SEM images, analysis of pellets from various milling conditions6 reveals that longer milling times decrease Al particle territory, indicating increase cohesion and optimal dispersion practices. Cast A356 MMNCs reveal that the condition of the pellet and ultrasonic treatment are paramount for improvement in tensile strength, showing up to 90% improvement in 0.2% proof stress when compared to as-cast. Software for analysing dendritic cores (DenMap) was created to analyse cast A356 MMNC samples, but it currently only applies to singlec rystal materials, which A356 MMNCs cast under current production methods are not.