Tensile behaviour of squeeze cast and forged short alumina fibre reinforced AA 6061

Abstract

The tensile properties of a composite consisting of 20 vol.-% short δ alumina fibres in an aluminium matrix (AA 6061) prepared by squeeze casting have been investigated, before and after 30% reduction by forging. By annealing the composite before forging, a 30% forging reduction could be achieved at room temperature, without crack formation. A reduction in mean fibre length from about 65 to 15 μm was observed but most fibre breaks were filled by matrix. By heat treating the composites after forging, their elongation to fracture was increased to about twice that of a similarly heat treated unforged composite of comparable strength. The improvement of ductility is attributed to break-up of the fibre skeleton structure inherited from the fibre preform. A model is presented that predicts that for these fibres an optimum effective reinforcement is achieved at fibre lengths of about 100 μm, which explains why the reduction in fibre length caused by forging does not result in significant strength loss.

MST/1720