Effect of surface modification on interfacial microstructures and mechanical properties of continuous CF/Al composites

The interface structure and infiltration effect between reinforcement (CFs) and Al matrix have a significant impact upon comprehensive properties of the resulting carbon-fibre-reinforced Al matrix (CF/Al) composites. In present study, Ni coatings with different thicknesses were evenly coated onto carbon fibres (CFs) via electroplating for the purpose of promote the interface combining effect and reduce adverse interfacial reaction betwixt CFs and Al matrix. The influence of pH value (2, 3, 4, 5, 6), current density (0.1 A, 0.2 A, 0.3 A, 0.4 A, 0.5 A, 0.6 A), electroplating time (2 min, 4 min, 6 min) on surface appearance and tensile strength of Ni-coated CFs were discussed. The results show that the Ni-coated CFs with excellent integrity and mechanical properties was obtained at a current density of 0.4 A and a pH of 5. Subsequently, twin-roll casting and T6 heat treatment process were used to fabricate CF/Al composites with varying Ni coating thicknesses. Using SEM, TEM and tensile property testing, the impact of Ni coating thickness (0 mu m, 0.35 mu m, 0.58 mu m, 0.76 mu m) on interfacial microstructures and mechanical characteristics of CF/Al composites were examined. The results exhibit that the 0.76 mu m Ni-coated CF/Al composites exhibit best UTS and elongation of 151.6 MPa and 11.7 %, respectively. This is due to a thicker Ni coating preventing the CFs against reaction with Al matrix during processing the composites, which reduces the generation of Al4C3 phase. However, when the coating thickness is 0.35 mu m, adverse chemical interactions occur at interface of Al-CFs, leading to the formation of an Al4C3 phase. Finally, the strengthening mechanism of Ni-coated CF/Al composites was analyzed, and its strengthening model was established. This study can provide a pratical route to prepare and applicate the high-quality continuous CF/Al composites.