Influence of metal powder premixing on mechanical behavior of dual reinforcement (Al2O3 (μm)/Si3N4 (nm)) in AA6061 matrix

The fabrication method of composite materials has significant influence on the mechanical properties of the materials. Establishment of proper bonding, dispersion and diffusion of reinforcement in the matrix are identified as principal characteristics which need to be taken care during the manufacturing of metal matrix composites. The current work has highlighted the impact of metal (Al) mixed dual size particle reinforcements (Al2O3 (μm) & Si3N4 (nm)) and the domination of silicon nitride nano particle in the composite system. The reinforcement powders were ball milled for 3 h. The matrix alloy used in this work was AA6061 which holds the applications in the construction of structures, aircraft and automobile bodies. The matrix alloy was melted and milled powders were added at 850 °C followed by stirring process. The tensile, Compression and Hardness tests were conducted to characterize the mechanical behavior of the prepared composites. The Optical Microscope and the Scanning Electron Microscopes were used to analyze the morphology of the as-cast and fractured surfaces. The composites of metal mixed reinforcements offered improved mechanical properties than the composites of unmixed reinforcement. Tensile characteristics [Ultimate Tensile Strength (72.3 MPa-153.2 MPa), yield strength (67 MPa-148 MPa), and ductility (2-8.3%)] were much influenced by pre mixed Si3N4 nano particles and its volume fraction in composites. The composites with dual reinforcement have shown superior tensile behavior than single reinforcement. The compression behavior [compression strength (253-361.74 MPa)] and hardness of the composites were dominated by single reinforcement with premixed Al2O3 particles. The dislocation density due to the presence of Si3N4 nano particle and proper bonding of hard Al2O3 particles in the matrix supported by Si3N4 nano particles were observed as strengthening mechanism in the composites with dual reinforcement.