Improving graphene distribution and mechanical properties of GNP/Al composites by cold drawing

Dispersion of graphene in aluminum matrix has been a key factor that affects the strengthening efficiency of graphene reinforced aluminum matrix composites. Here, GNP/Al composites reinforced with 0.4 wt% and 2.0 wt% graphene nano-platelets (GNP) were fabricated by powder metallurgy (PM) followed by a multi-pass cold drawing at ambient temperature in order to eliminate the GNP aggregates. The microstructure evolution and the mechanical properties of the GNP/Al composites were investigated. Results showed that GNP cracked into pieces along the drawing direction, leading to improved GNP distribution. GNP aggregates were eliminated in 0.4 wt% GNP/Al at an equivalent drawing strain of 6.00 compared with that in the as-extruded composite, while some still exist in the 2.0 wt% GNP/Al composite. The ultimate tensile strength (UTS) of as-drawn 0.4 wt% GNP/Al composites was ~52% higher than that of the Al alloy. While, the mechanical properties of 2.0 wt% GNP/Al composites deteriorated because of the existence of GNP aggregates. The dispersed GNP with strong interfacial bonding in 0.4 wt% GNP/Al composites exhibited significant load transfer strengthening effect, which contributed to the improvement in UTS. The strengthening efficiency (R) of graphene in the cold-drawn composite wires reached ~80%, which is comparable to that of the composites fabricated by wet chemistry method.