Microstructure and mechanical properties of ABOw and nickel-coated MWCNTs reinforced 2024Al hybrid composite fabricated by squeeze casting

Homogeneous distribution of multi-walled carbon nanotubes (MWCNTs) in aluminum matrix composites and optimization of the MWCNTs-aluminum interfacial strength are challenging for MWCNTs/Al metal-matrix composites (MMCs). Here, in order to improve the wettability and the interfacial bonding between MWCNTs and aluminum matrix alloy, a uniform nickel layer was created on MWCNTs by electroless plating. Hybrid preforms comprising of aluminum borate whisker (ABOw) and MWCNTs with/without nickel coating were prepared. It was found that the presence of ABOw and nickel coating ensured the homogeneous distribution of MWCNTs in composites. The presence of the nickel coating on MWCNTs also helps in decreasing the porosity of composite prepared by squeeze casting technique. Compared with ABOw/2024Al and ABOw + MWCNTs/2024Al composites, improvements in elongation and hardness were obtained in the ABOw + MWCNTs(Ni)/2024Al composite, which may be attributed to the reduced porosity, increased interfacial bonding strength and the crack deflection induced by dispersed MWCNTs. However, the addition of MWCNTs did not change the main fracture mechanism: ABOw break and ABOw-aluminum interfacial de-bonding dominated the fracture process in ABOw and MWCNTs(Ni) reinforced composites.