FABRICATION AND CHARACTERIZATION OF AL-AL4C3 NANOCOMPOSITE BY MECHANICAL ALLOYING

Abstract

Aluminum carbide ( Al 4 C 3) seems to be an ideal reinforcement for producing aluminum matrix composites. Al 4 C 3 has high hardness and shear strength as well as a high melting point. The dispersion of Al 4 C 3 particles in the matrix produces a pinning effect that reduces aluminum grain growth, which improves the mechanical properties. In this study, aluminum powders were mixed with 4.5 wt.% graphite and mechanically alloyed using a high-energy ball mill in order to produce Al - Al 4 C 3 nanocomposite. The structural evaluation of powder particles after different milling times was studied by X-ray diffractometry, scanning electron microscopy and microhardness measurements. The aluminum crystallite size estimated with broadening of XRD peaks by Williamson–Hall formula. XRD results suggested that the grain size of aluminum decreased to nanometer range (30 nm) during ball milling. No Al 4 C 3 formed during the mechanical alloying process. Milled powders were then annealed at 300-600 °C for 1 h under argon atmosphere. Annealing at temperatures higher than 300 °C led to formation of Al 4 C 3 phase which increased as annealing temperature increased. Aluminum grain size remained in nanometer range after annealing process. The microhardness of powder particles increased after annealing. Both effects are due to the formation of nanosized Al 4 C 3 particles.