Development and Property Evaluation of Alumina Nano-Particle Reinforced Cast Metal Matrix Composites

Lightweight Metal Matrix Nano-Composites (MMNCs)(metal matrix with nano-sized ceramic particles) based on aluminium and magnesium has emerged as an important class of materials, finding increasing applications in automobile, aero-space and space industries, in their quest for achieving better fuel economy. It would be advantageous to produce low-cost as-cast bulk lightweight components of MMNCs. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal. Particle reinforced MMC succeeds in synergizing the metallic matrix with ceramic particle reinforcements to result in improved strength, particularly at elevated temperatures but adversely affects the ductility of the matrix. Nano-sized alumina particles have been generated by milling mixture of aluminium and manganese dioxide powders mixed in ratio of 1:7 by weight and the particle size has been varied by milling in a vibratory disc mill (RS200, Retsch, Germany) for 450 minutes at 700 rpm. Micrographs observed under Transmission Electron Microscope (TEM) have revealed the presence of nano-sized γ-alumina particles as a consequence of milling and the particles in the milled powder mix may be divided into three broad size classes of 1-10 nm, 10-200nm and above 200nm. The amount of addition varies from 1 to 4 wt % in steps of 1 wt % of particles after drying is added to molten metal/alloy and the resulting slurry is cast in a mold to get cast nano-composite. The microstructure of cast composites when analyzed by TEM and FE-SEM, confirm separate occurrence of nano-particles without agglomeration and its mechanical properties show significant improvement in terms of yield strength, tensile strength and ductility.