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Abstract
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This study evaluated the influence of mechanical milling time on the physical, mechanical, and microstructural properties of Al metal matrix composites (MMCs) incorporating ZrB2 ceramic reinforcement. The mixing powders of aluminum with zirconium diboride were mechanically milled at different times. Then, the achieved composite powder was heated, compacted, and turned into bulk material by equal channel angular pressing (ECAP) at 250°C. SEM micrographs indicated that the size of the obtained particles decreases by increasing the mechanical alloying time by up to 18 hours. However, the particle size has increased after this time. The average size of fine particles reached 823nm using mechanical alloying for 18 hours, while coarse particles were 8µm. The size calculation of crystallites using XRD examination implied that the rate of crystallite size reduction after 12 hours of mechanical alloying is gradually reduced and reached its lowest level after 18 hours. Then, increasing the mechanical alloying time led to an increase in the size of the crystallites and a decrease in the lattice strain. The microstructure of resultant bulk composites has been characterized by optical microscopy (OM) and SEM. The bulk composite samples processed by the ECAP method, with an optimum amount of ZrB2 (5 wt.%), had a relative density, hardness, shear yield stress, and ultimate shear strength of 99.3%, 170 HV, 125 MPa and 151 MPa, respectively, utilizing powders which were mechanically milled for 24 hours.
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