Aging behavior and tensile response of a SiCw reinforced eutectoid zinc-aluminium-copper alloy matrix composite

A SiC whisker-reinforced eutectoid zinc-aluminum-copper alloy matrix composite (SiCw/ZAC) was fabricated via a vacuum pressure infiltration technique and investigated comprehensively by comparison with the unreinforced ZAC alloy. The microstructure of the composite was composed of SiC whiskers, Al3Cu5Zn phases and eutectoids of α (Al-rich solid solution) and η (Zn-rich solid solution) with an amount of Al3Cu5Zn phase 1.5 times that in the ZAC alloy. The density and coefficient of thermal expansion of the composite were 4.81 g/cm3 and 21.45 ppm/K, respectively, lower than those of the ZAC alloy. Compared with the ZAC alloy, the composite had a lower peak aging temperature but a much higher peak aging hardness. The addition of SiCw dramatically increased the strength and elastic modulus of the ZAC alloy but greatly decreased the ductility. The ZAC alloy was ductile and fractured in the mode of microvoid coalescence. In contrast, the SiCw/ZAC composite was brittle. In addition to SiC whiskers, brittle Al3Cu5Zn phases were also the nucleation sites of microcracks and hence also responsible for the much lower ductility of the composite.