Hierarchical microstructure architecture: A roadmap towards strengthening and toughening reduced graphene oxide/2024Al matrix composites synthesized by flake powder thixoforming.

Graphene as one of the best reinforcements for improving the comprehensive properties of the composites has attracted extensive attention. However, the severe aggregation of graphene in the matrix obviously weakened the strengthening efficiency. A novel method, flake powder thixoforming (FPT) that combines both the advantages of flake powder metallurgy and thixoforming, was proposed to construct the FPT-0.4 wt%RGO/Al composite with hierarchical microstructure that reduced graphene oxide (RGO) only uniformly distributed into the local regions of secondary solidified structures (SSSs). The ultimate tensile strength (UTS, 439 MPa), yield strength (YS, 294 MPa) and elongation (8.5%) of FPT-0.4 wt%RGO/Al composite fabricated by FPT were increased by 45.8% and 44.8% and decreased by 44.1% compared with the 2024Al alloy, respectively. Moreover, a 34.9% enhancement in YS and a 54.5% improvement in elongation were achieved when compared with the HEM-0.4 wt%RGO/Al composite prepared by high energy milling (HEM). The RGO-rich zones in the FPT-0.4 wt%RGO/Al composite behaved as reinforcing units that can sustain the tensile stress and thus strengthened the matrix. Simultaneously, crack deflection and bridging contributed by the RGO-free zones effectively toughened the composite. FPT is promising for strengthening and toughening the RGO/Al composites by tailoring the spatial arrangement of RGO to form hierarchical microstructure. Image 1 • Flake powder thixoforming technology was developed. • A FPT-0.4 wt%RGO/Al composite with hierarchical microstructure was fabricated. • The strengthening and toughening are achieved by tailoring the dispersion of RGO. [ABSTRACT FROM AUTHOR]