Effect of short-carbon fiber and nano-carbon fiber as reinforcement on microstructure and properties of hot-rolled aluminum matrix composites

The selection of reinforcement is an important part of the design and application of composites. It is important to elucidate the reinforcement diameter's effect on the composites microstructure and properties. In this study, short-carbon fiber (SCF)- and vapor-grown carbon nanofiber (VGCNF)-reinforced aluminum (Al) matrix composites were prepared by spark plasma sintering (SPS). The effects of different reinforcements on the microstructure evolution and properties of the hot-rolled composites were investigated. The results demonstrate that the SCF is more homogeneously distributed in the Al matrix, and the VGCNF is agglomerated because of its smaller size. The nano-hardness value of the interface between VGCNF and Al matrix is 39.91HV, which is lower than the 51.27HV of the interface between SCF and Al matrix. TEM results show that the formation of continuous amorphous carbides gives a well-interfacial bonding between SCF and Al matrix. The gaps between the VGCNF and the Al matrix result in low interfacial hardness. Due to the formation of Al4C3 crystal, the nano-hardness of the interface between SCF and Al matrix is increased by 111.25% after hot rolling. In addition, due to the aggregation between VGCNF, the heat transfer efficiency of VGCNF is 60.73%, lower than 76.91% of SCF. The yield strength of SCF/Al is higher than that of VGCNF/Al before and after hot rolling, which is attributed to the load-bearing effect of SCF and the generation of rotational Gauss components.