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Graphene oxide-carbon nanotubes hybrid reinforced aluminum matrix composites (GO-CNT/Al) were prepared by powder metallurgy followed by hot extrusion. The strength of the composites was improved by the synergistic effect of carbon nanotubes, in-situ Al 4 C 3 and graphene oxide. Moreover, due to the partially recrystallization of Al matrix promoted by Al 4 C 3 , the matrix exhibits a bimodal grain distribution, which helps to enhance strain-hardening and consequently uniform tensile ductility at high flow stresses. Hence the bimodal grain structure of the matrix combined with the nano-reinforcements leads to enhancing of the strength and ductility synergy. The composite shows a high tensile strength of 249 MPa (175 MPa of pure Al) and keeps almost similar tensile ductility with pure Al (uniform elongation of ~23.1%). • The structure changes of graphene oxide and carbon nanotubes during ball milling were revealed. • The influence of reinforcement dimension on the strengthening mechanism of aluminum matrix composites was emphasized. • The balance between strength and ductility is achieved by different dimension reinforcements and bimodal grain distribution. [ABSTRACT FROM AUTHOR]

High elongation aluminum matrix composites reinforced with carbon nanotubes (CNTs) were prepared by flake powder metallurgy, and densified by hot extrusion with a high extrusion ratio. After hot extrusion, fine and equiaxed grains were obtained in 2 wt% CNT/Al composite, and interfacial product (Al 4 C 3) as well as bridge-connected CNTs aligned along the extrusion direction were found both in 1 wt% CNT/Al and 2 wt% CNT/Al composites. Both composites obtained high elongation while their strength was enhanced. Especially the elongation of 2 wt% CNT/Al composite is comparable to that of pure Al prepared by the same method, which reached about 30%. The good ductility mainly attributes to firm interfacial combination between CNTs and matrix, fine and equiaxed grains formed by dynamic recrystallization during hot extrusion, and bridge-connected CNTs aligned along the extrusion direction. Unlabelled Image • CNT/Al composites and pure Al were fabricated by flake powder metallurgy • The dynamic recrystallization occurred in 2 wt% CNT/Al composite during hot extrusion • The elongation of 2 wt% CNT/Al composite is comparable to that of pure Al prepared by the same method • The bridge-connected CNTs is helpful to improve the elongation of composite [ABSTRACT FROM AUTHOR]