Thermal of aluminium-based metal matrix composites studied by mechanical spectroscopy

Abstract

The mechanical behaviour of alurninium-based composites reinforced with short Al2O3 SAFFIL fibres has been investigated by mechanical loss and elastic shear modulus measurements during thermal cycling. A mechanical loss maximum, which is not present in the unreinforced alloys, has been observed during cooling near 200K. It originates in the relaxation of thermal stresses at the interfaces due to the differential thermal expansion between matrix and reinforcement. The maximum height increases with the volumetric fibre content. In addition, if the matrix strength is increased by the appropriate choice of alloy and thermal treatment, the maximum diminishes and shifts to lower temperatures. No damage accumulation at the interfaces has been detected during prolonged thermal cycling in the range of 100-500K. A description of the damping behaviour is presented in terms of the development of microplastic zones, which surround the fibres. Such zones, in which dissipation takes place, would be beneficial for increasing the lifetime of MMC components in service conditions.