AGING RESPONSE AND MECHANICAL-PROPERTIES OF A SICP/AL-LI (8090) COMPOSITE

The ageing kinetics of a silicon carbide particle-reinforced Al-Li (8090) matrix composite and unreinforced' alloy, both made by spray forming, were investigated. Ageing treatments, without any straining after solutionizing, and with a 2% plastic strain after solutionizing, were employed. The peak ageing times of the matrix in the composite was shorter than that of the unreinforced alloy. The enhanced hardening rate of the matrix in the composite was attributed to the higher dislocation density induced as a result of the plastic deformation occurring at the particle/matrix interface. This plastic deformation is a result of the large difference in the coefficient of thermal expansion between the particles and matrix. Subjecting the samples to a 2% plastic strain reduced the peak ageing times even further. The tensile strength of the composite samples was marginally higher than that of the unreinforced alloy. Samples subjected to 2% plastic straining prior to ageing also exhibited higher strength values. The strain to failure of all the samples did not recover in the over-aged state.