Document Type : Research Paper
Authors
Abstract
In this study, Aluminium2024- Graphite composites containing 5, 10, 15 and 20 weight percent of graphite were produced by solid assisted melt disintegration (SAMD) technique which resulted in production of Al/Gr powder mixtures which subsequently consolidated and sintered for preparation of Al/Gr composites. In this technique, powder mixture was prepared by addition of flake graphite (mean diameter 55 ?m) to the molten 2024 aluminum alloy. The slurry was stirred at a specified time-temperature cycle before air-cooling. For determining the optimum processing conditions, four time-temperature cycles were used. In these cycles the Al 2024 alloy was stirred in liquid and/or semisolid conditions in the presence of graphite powder. The screen test as well as laser particle size analysis demonstrated a wide size distribution of the resultant Al/Gr powder mixture. The graphite content of the powder mixture in different size ranges quantified by chemical dissolution method exhibited a higher percentage for smaller size bands. SEM studies confirmed the attachment of some graphite particles to the coarse aluminum powders Powder mixtures with different graphite contents (0-20wt%) were compressed uniaxially at optimum pressure. The compacted samples were sintered at suitable temperature. Fracture surface of compressed and sintered samples were studied by SEM. It was concluded that with using the optimum time-temperature cycle, the time of process decreases and the yield of produced powders increases. Powder mixtures produced by this method exhibited a wide size distribution. SEM studies confirmed that the graphite flakes were adhered to the surface of coarse Al powder particles while in the smaller size bands a mixture of free graphite flakes and Al powders could be observed. The SEM studies on the fracture surface of Al/Gr composites produced by the present method confirmed a relatively uniform distribution of the graphite particles in the matrix alloy.
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