Mechanical properties and microstructure of a P/M aluminium matrix composite with δ-alumina fibres and their relation to extrusion
Saffil short fibre-reinforced aluminium composites have been prepared via a powder metallurgy route. Three different reduction ratios of extrusion were investigated. The tensile mechanical properties at room and elevated temperature and the microstructure, with emphasis on fibre length, were evaluated. The reduction ratio did not influence mean fibre length, implying that during the extrusion the main fibre breakage occurred in the initial compaction stage. The relative strengthening of the unidirectionally reinforced composites at room temperature is low and depends on extrusion reduction ratio. At elevated temperature the strength of the composites in the longitudinal direction is significantly higher compared to that of the base alloy. At 250°C, improvements were obtained of 15%, 24% and 43% for Vf = 0.048, 0.100 and 0.200, respectively. It is suggested that strengthening is possible by the combined effect of a high ductility of the matrix and the resistance to plastic flow exerted by dislocations and stress fields around aligned fibres. All composites contain highly fibre-enriched layers, with bad internal cohesion. They originate from fibre clusters and form severe macroscopic defects during machining operations. Despite that, the tensile properties in the longitudinal direction are reasonably good.
KeywordsDuctility Longitudinal Direction Powder Metallurgy Fibre Length Aluminium Matrix
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