JMS_V2_N4_RP3 Pardeep Sharma Dinesh Khanduja Satpal Sharma Journal on Material Science 2347–615X 2 4 13 19 Aluminium Matrix Composites, Ball Milling, Optical Microscope, Physical properties, Scanning Electron Microscope, Silicon Nitride In case of hybrid composites, the reinforcements either float or sink in the metal matrix due to density mismatch between the combined reinforcement and metal matrix which resulted into clustering and agglomeration of reinforcement particles into metal matrix. To avoid this clustering and non-uniform distribution of reinforcement particles in the matrix, a novel approach was used to manufacture hybrid composites. In this research work, silicon nitride and graphite ceramic powder were separately milled before composite fabrication. This ball milled powder was further used in the manufacturing of hybrid composites by stir casting process in protective inert atmosphere. The ball milled Si3 N4 /Gr ceramic powder were varied from 0 to 12 % in the matrix in a step of 3 and effect of varying reinforcement on the microstructures and physical properties were investigated. The microstructures of the manufactured hybrid composites were examined using optical microscope and the physical properties investigated include density and porosity. Ball milling results showed a more homogeneous microstructure with rough morphology of combined powder after 100 hours of ball milling by the scanning electron micrographs and the final density of ball milled powder after 100 hours was 2.81g/cm power 3. The result of hybrid composites showed that with the addition of ball milled Si3N4 /Gr the density increased by 10.33% with an increase in porosity from 0.37 % to 1.64% as the weight % of ball milled Si3N4 /Gr, reinforcement particles increased from 0 to 12 %. The optical microstructure revealed a reasonably uniform distribution of reinforcement particles into the metal matrix. January – March 2015 Copyright © 2015 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=3122