Investigation of particle size and reinforcement content on mechanical properties and fracture behavior of A356-Al2O3 composite fabricated by vortex method

The aim of the present study is to investigate the effect of alumina particle size and its amount on relative density, mechanical properties, and fracture behavior of Al - Al2O3 composite. To manufacture micro and nano-composites, alumina particles with various sizes of 50 mm, 10 mm, and 20 nm were separately milled with aluminum powders, and subsequently different volume fractions of milled powders were injected by argon gas into molten alloy and incorporated into A356 matrix by a mechanical stirrer (vortex method). Composites were fabricated at various casting temperatures, viz. 750, 800, and 900 degrees C. Microstructural characterizations revealed that the dendrite size of the Aluminum matrix nano composite (AMNCs) is smaller than that of the non-reinforced alloy. The Scanning electron microscope (SEM) micrographs revealed that the Al2O3 particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. Nano-particles were dispersed uniformly in the matrix when the volume fraction of nano-particles in the composite was less than 3.5 vol.%. The porosity content of the composites increased with increasing volume fraction and decreasing particle size. Also, hardness and tensile strength of the composites improved with decreasing particle size and increasing reinforcement content. The significant improvements in hardness and tensile strength were respectively attained in the nano-composites, reinforced with 1.5 and 2.5 vol.% Al2O3 nano-particles. Alumina particle cracking was observed in the fracture surface of the micro-composites. Agglomerated nano-particles were observed on dendrites in the fracture surface of nano-composites.