Revealing the strengthening and toughening mechanisms of Al-CuO composite fabricated via in-situ solid-state reaction

Due to native deficiency of the interfacial mismatch between Al2O3 and Al-melt, as well as micron-Al2O3 segregation at matrix grain boundaries (GBs), achieving both high strength and fracture toughness has been the long-lasting challenge for Al-CuO composite fabricated by conventional casting. Herein, we report a novel manufacturing of Al-CuO composite via shift-speed ball-milling (SSBM) of Al-5 wt.% CuO powders and afterwards subjected to hot-pressing (HP) as well as heat treatment. Comprehensive characterization shows that in-situ generation of the two types of Al2O3 with intragranular distribution, including δ*-Al2O3 particles (~200 nm) and γ-Al2O3 whiskers (length of ~150 nm, thickness of ~20 nm), was governed by a diffusion-assisted nucleation-regime ascribing to the intense thermal effect of Al-CuO reaction. The size and spatial distribution of Al2O3 were emphasized to address their contribution to the high mechanical performance of the composite, which exhibits a tensile strength of ~481 MPa and fracture elongation of ~16.8 %. Meanwhile, the toughening mechanism of present Al-CuO composite was rationalized on basis of the "dislocation punched zone" and "plastic zone" affected by Al2O3. Both the theoretical analysis and fracture morphology support a reinforcements-matrix interface failure mechanism and the non-uniform distribution of Al2O3 consisting alternant "rich/poor zones" can markedly contribute to the high toughness. The present findings may provide a promising strategy to achieve an intragranular distribution of nano-sized reinforcements in Al-metal oxides composites, which enables increasing strength and ductility of the metal matrix.