Mechanical properties and microstructure of A356 alloy reinforced AlN/MWCNT/graphite/Al composites fabricated by stir casting

In this experimental research work, the metal matrix composites of A356 alloy were prepared by reinforcing different shaped particles Aluminium Nitride (AlN), Multi-Walled Carbon Nano Tube (MWCNT) and graphite (Gr). The main objective of this research work was to investigate the influence of different shaped reinforcement in the microstructure and mechanical behaviour of composites. The reinforcements (AlN & MWCNT) were added as 0.5, 0.75, 1 and 2 vol% and the graphite was maintained in 0.5 vol%. The composites were fabricated using stir casting followed by ultrasonic vibration treatment. The tensile, compression and Brinell hardness test were carried out by following ASTM standards. The characterization of reinforcements, castings and fractured surfaces was performed using Optical Microscope (OM) and Scanning Electron Microscope (SEM). The mechanical tests and characterization results revealed that there was a significant influence of morphology of reinforcements on mechanical properties of the materials. Particle strengthening and grain refinement strengthening were found to be operative in the composites. The SEM micrograph of fractured surface of composites with MWCNT exhibited the crack bridging effect as strengthening mechanism apart from particle strengthening. The porosity and cluster of reinforcements were observed in the composites with MWCNT more than 1 vol% of and AlN 0.75 vol%.