Investigation of the microstructure, electrical and mechanical properties of Al-CNTs-B₄C composite prepared by double-step stir casting for power transmission conductor

Abstract

Monolithic aluminium alloy is a modern engineering material that is in high demand owing to its excellent performance and versatility. It has a high electrical conductivity, low density, high strength- to- weight ratio, and high resistance to corrosion. However, it lacks adequate resistance to creep, fatigue, stable microstructure, and strength at elevated temperatures. To overcome these deficiencies, aluminium matrix composites are developed. This work focuses on an experimental investigation of the microstructure, mechanical strength, and electrical conductivity of Al-CNTs-B4C composite consolidated by a double-step stir casting technique. An X-ray diffractometer, transmission electron microscopy, and a field-emission scanning electron microscope fitted with energy dispersive X-ray spectroscopy were used to characterize the start-up powders and the cast samples. A Brinell tester was used to measure the microhardness of the cast samples. A four-point probe meter was used to determine the electrical conductivity. The microstructural results revealed formation of Al4C3 and Al3BC intermetallics, B4C phase and amorphous carbon precipitate. Marginally improved electrical conductivity of 33.33 x 107 S/m (65.1% IACS) was obtained with Al-5CNTs-15B4C, together with high microhardness of 725.72 MPa. The microhardness improved by 94.7% over monolithic pure Al. The double-step stir casting enhanced the homogenous dispersion of the reinforcements. The improvements in the mechanical properties and electrical conductivity were attributed to the synergy between B4C and CNTs which induced Orowan looping, load transfer effect, plastic deformation and dislocation pinning in the composite. It is recommended that this composite will perform creditably in power transmission.