Damping behaviour of aluminium/short glass fibre composites

The thermo-mechanical behaviour of both as cast and aged Al7075/E-glass short fibre composites was investigated as a function of temperature using resonant-bar analysis. The composites were prepared by the melt-stirring technique with 2, 4 and 6% by weight of short E-glass fibre. The damping capacity showed an initial increase reaching a peak value and decrease with the increase in operating temperature. A similar trend of damping behaviour was observed during ageing with initial increase reaching a peak and thereafter decreased. The attainment of peak is advanced in case of composites due to the presence of glass fibres, which significantly accelerate the ageing and precipitation kinetics in matrix alloy. This acceleration is attributed to the decrease in incubation time for nucleation and growth of precipitates resulting from an increase in dislocation density due to coefficient of thermal expansion (CTE) mismatch between the matrix and the reinforcement. The damping mechanisms, which include contribution of microstructure changes and ageing effect on precipitation along grain boundaries, are discussed using TEM, EDS and optical microscope.