Development of A356/Al2O3 + SiO2 surface hybrid nanocomposite by friction stir processing

Surface hybrid nanocomposite layers reinforced with nano-sized Al2O3 and SiO2 powders on the A356 cast aluminum alloy matrix were developed by friction stir processing (FSP). The optical and scanning electron microscopy (SEM) were used to study the microstructure of samples, as well as to investigate the size and morphology of the reinforcement powders. Microhardness and nanoindentation tests were applied to characterize the mechanical properties of the samples. To examine corrosion behavior of the samples, the potentiodynamic polarization and electrochemical impedance spectroscopy were used. In addition, the corroded surfaces were investigated by SEM. FSP of the alloy leads to the fragmentation of coarse silicon needle-shaped particles and coarse dendrites of primary aluminum, reduction in porosity and uniform distribution of fine silicon particle with average size about 3 pm in the aluminum substrate. Furthermore, the microstructural analysis showed a uniform distribution of reinforcement particles inside the nugget zone. The surface hybrid nanocomposite resulted in enhanced mechanical and corrosion properties compared with A356 Al alloy and the FSPed A356.