Enhanced combination of strength and ductility in ultrafine-grained aluminum composites reinforced with high content intragranular nanoparticles

Simultaneous enhancement of the strength and ductility in metal-matrix nanocomposites with high content nano-reinforcements is crucial for the development of novel composite materials. Here SiC/Al nanocomposites with ultrafine Al grains and intragranular 10 vol% SiC nanoparticle were prepared by mechanical alloying and hot pressure sintering followed by hot extrusion. The results show that nanocrystalline Al grains and uniformly distributed SiC nanoparticles (SiC_np) in the composite powders are obtained after ball-milling. The prior particle boundary (PPB) in the composite powders cannot be fully removed by sintering at 580 °C under 20 MPa, but can be eliminated by subsequent hot extrusion at 450 °C with a ratio 25:1. The extruded nanocomposites possess ultrafine Al grains with diameter 320 nm and intragranular SiC_np created by the dynamic recrystallizations (DRX). Such optimal microstructure favors a significant improvement of 284% in yield strength (YS) and 259% in ultimate tensile strength (UTS) compared with monolithic Al, and more interestingly, maintains an elongation up to 12% due to the homogeneous nanoparticles in fine Al grains. Theoretical analysis shows that the dominant strengthening factor is Orowan strengthening related to the high content intragranular SiC_np, with second factor grain boundary strengthening due to ultrafine Al grains.