The deformation behaviour of bimodal sized Al2 O3 /Al nanocomposites were investigated by hot compression tests conducted in the temperature range 350-500°C and strain rates of 0.001, 0.01 and 0.1 s-1 . The dynamic recrystallisation behaviour of the nanocomposites strongly depended on the forming parameters. The bimodal sized Al2 O3 particles played a crucial role in the recrystallised microstructure. The addition of bimodal sized Al2 O3 particles led to a significant increase of activation energy of plastic deformation, corroborating the enhanced resistance of the nanocomposite to hot deformation. This was also reflected by the increased compressive yield strength in the nanocomposite due to both dislocation strengthening caused by n-Al2 O3 and preventing the grain growth due to the presence of μ-Al2 O3 at grain boundaries. It was found that with the decrease of Z values, local strain induced by deformation was released and the grain size of aluminium matrix gradually increased, indicating that the main softening mechanism of the bimodal sized Al2 O3 /Al nanocomposites was dynamic recrystallisation (DRX). The lower the Z value was, the easier the DRX occurred. The highly beneficial role of the bimodal sized Al2 O3 reinforcement in improving the high-temperature performance of aluminium matrix nanocomposite was discussed.
Keywords: Bimodal reinforcement; constitutive modelling; hot forming; metal matrix nanocomposites (MMCs); spark plasma sintering (SPS).
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