Microstructural Evolution of Aluminum-4043/Nickel-Coated Silicon Carbide Composites Produced via Stir Casting

Aluminum-silicon carbide (Al/SiC) metal matrix composites have become a promising engineering material owing to its high strength to weight ratio. However, there is formation of aluminum carbide phase which is deleterious to the physical properties of the composites and needs to be eliminated. In this paper, the stir casting of Al-4043/Ni-coated SiC composites was investigated and reported. The Al/SiC composites were produced by melting Al-4043 lumps, injecting SiC powder with varying weight fraction into the Al melt and pouring the stirred mixture into a sand mould at 680°C. Prior to the use of the SiC powder, the powder particles were coated with 15 µm thickness of nickel to prevent dissolution of the SiC into the Al melt. The microstructure of the composites was characterized using optical and scanning electron microscopes to reveal the microstructural features and phases present. The result showed that composite microstructure was characterized by filament-like and particulate-like features which are uniformly distributed in the Al matrix. The volume fraction of the filaments increased with increasing SiC reinforcement fraction employed during processing. The microstructure formed is predominantly Al-SiC eutectic microstructure with uniformly dispersed SiC particles. The Ni coating has presumably prevented the formation of Al4C3 and promoted the formation of eutectic microstructure. A higher strength is anticipated with the filaments randomly oriented and uniformly dispersed in the Al-4043/Ni-coated SiC composites.