Effects of strontium modification on A356: Delta-alumina fibre metal matrix composites

A study has been conducted to determine the effects of strontium modification of the eutectic phase in an Al-Si-{dollar}delta{dollar}-alumina fibre metal matrix composite system. The composite was manufactured by pressure infiltration of cylindrical SAFFIL fibre preforms with A356 aluminum alloy using the squeeze casting process. Observations were made on the effects of strontium modification, heat treatment (F versus T6) and fiber binder (silica or alumina) on the resultant microstructure and room temperature mechanical properties.; Strontium concentrations of 135 ppm were found to be sufficient to cause modification of the eutectic silicon in the squeeze cast A356 alloy. The addition of strontium decreased the strength, but increased the percent elongation of the unreinforced alloy. Strontium modification was found to have no discernible effect on the mechanical properties of the composite material. Using a preform temperature of 600{dollar}spcirc{dollar}C, reactivate between the molten aluminum and the silica fibre binder was not a factor in the modification of the eutectic silicon under the casting conditions employed here. Demodification of the eutectic silicon was found when a preform temperature of 700{dollar}spcirc{dollar}C was employed. No difference was found between composites formed using silica or alumina bound fibre preforms. T6 heat treatment of the composite specimens promoted a stronger fibre matrix bond although a significant increase in mechanical properties was not realized.