Architecting Strength: Innovative Microstructural Design of Aluminum/Alumina Nanocomposites via Cold-Welded Flaky-Shaped Particles and Pressure-Assisted Sintering

Aluminum/alumina (Al/ Al2O3) nanocomposites with three different microstructural architectures were prepared using flake powder metallurgy, which involves the conversion of spherical Al powder into nanoflakes by ball milling, the introduction of Al2O3 by natural oxidation, the control of the powder microstructure by cold welding, and then powder by densification, sintering, and extrusion. The experimental results showed that the shape of the Al matrix grains and the distribution of native Al2O3, the so-called Al/Al2O3 architectures, could be precisely controlled by BM. The nanolaminate architecture, in which the Al2O3 nanoplatelets were aligned along the boundaries of lamellar or elongated grains, exhibited a more balanced combination of tensile strength and ductility than the random architecture with non-uniformly distributed Al2O3 nanoplatelets within equiaxed grains. This improvement can be attributed to the combined effect of higher Al2O3 strengthening efficiency and better work hardening ability. The research results suggest that the presence of Al2O3 nanoplatelets at high-angle grain boundaries significantly hinders the main mechanism of subgrain rotation for the formation of new boundaries. Moreover, the simulation accurately predicts the higher degree of grain faceting in finer-grained samples, which is consistent with the experimental data indicating more pronounced hexagonal grain shapes. Consequently, flake powder metallurgy offers a promising approach for the production of strong and ductile Al- matrix composites through the design of their microstructural architecture.