Internal friction behavior in SiC particle reinforced 8090 Al–Li metal matrix composite

The mechanism of thermal stress relaxation was investigated at temperatures below room temperature for the metal matrix composite (MMC) Al–Li 8090/SiC. The internal friction technique has been used. Several cycles from 453 to 100 K were used in order to measure the internal friction and the dynamic modulus of the material. An internal friction peak has been observed in the MMC when cooling from 453 K. This peak is linked to the thermal stresses caused by the difference of the thermal expansion coefficients of the matrix and the reinforcement. It is concluded that thermal stresses are relaxed by microplastic deformation. Furthermore, the influence of the microstructure, in particular, the precipitation process, on the internal friction peak associated with microplastic deformation has been analysed. The variation of the dynamic modulus is related to the different stages of precipitation.