Enhanced precipitation hardening in an alumina reinforced Al–Cu alloy matrix composite

An alumina reinforced Al–Cu alloy matrix composite was prepared by reaction sintering of Al and CuO powders. Precipitation hardening by further aging the composite at 250 °C was studied. In situ formed micron-sized alumina particles were present in the Al(Cu) matrix of the un-aged composite, while additional nanometer-sized Al2Cu rods were obtained in the matrix of the aged composite. Both hardness and bending strength were enhanced after the composite was aged. In the bending test, the sample was plastically deformed before fracture. Microstructural analysis revealed that the size of dimples found in the fracture mouth of the un-aged composite was micron-sized, and that in the aged composite was much smaller. It was evident that when the composite was subjected to stress, micron-sized alumina particles were responsible for the formation of cracks in the un-aged sample, while in the aged sample, Al2Cu nanorods were the dominant nucleation sites for crack growth.