Effect of Ball Milling on the Tensile Properties of Aluminum-Based Metal Matrix Nanocomposite Developed by Stir Casting Technique

Combining ball milling with stir casting in the synthesis of nanocomposites is found effective in increasing the strength and ductility of the nanocomposites. In the first step, the nanoparticles used as reinforcement are generated by milling a mixture of aluminum (Al) and manganese dioxide (MnO₂) powders. A mixture of Al and MnO₂ powders are mixed in the ratio of 1:2.4 by weight and milled at 300 rpm in a high-energy planetary ball mill for different durations of 120 min, 240 min, and 360 min to generate nano-sized alumina (Al₂O₃) particles. It is supposed that the powders have two different roles during milling, firstly, to generate nano-sized Al₂O₃ by oxidation at the high-energy impact points due to collision between Al and MnO₂ particles, and secondly, to keep nano-sized Al₂O₃ particles physically separate by the presence of coarser particles. In the second step, 0.5 weight percent (wt%), 1 wt%, 1.5 wt%, and 2 wt% of the generated Al₂O₃ nanoparticles are reinforced in molten aluminum-magnesium (Al-Mg) alloy matrix via stir casting to synthesize nanocomposites. The effect of milling on the microstructure of the powder mixture before and after milling has been studied with the use of a scanning electron microscope (SEM) and X-ray diffraction analysis (XRD). The microstructure of the cast composites is examined under SEM, and the fractured surface of the tensile specimens is analyzed through SEM fractographs. Ball milling of reinforcement before adding to the melt brings considerable improvement in the integration and uniform dispersion of the milled particle in the Al-Mg alloy matrix melt, which leads to improvement in the strength and ductility of the cast nanocomposites.