Effect of CNTs on microstructure, mechanical and wear properties of the AZ91–3B₄C–3SiC–xCNTs composites

This article presents a study on the effect of adding carbon nanotubes (CNTs) (0, 0.5, 1 and 2 wt-%) and hot extrusion on the microstructures, mechanical properties, and wear behaviour of AZ91–3B4C–3SiC hybrid composites. The matrix alloy is AZ91 Mg alloy which primarily consists of 9 wt-% Al and 1 wt-% Zn. A mechanical-induction stir casting process was used to add CNTs to the composite. XRD patterns and EDX analysis showed that all composites have a microstructure of α-Mg, Mg17Al12, SiC and B4C. The outcomes demonstrated that the Mg17Al12 networks can be significantly thinned by the additional CNTs. The hot extrusion also dispersed the B4C and SiC particles in the structure, improving the particle-stimulated nucleation (PSN) plus twinning mechanism, but the presence of micron particles caused stress concentration, which did not affect the composites’ strength and elongation. The wear behaviour of the as-cast and extruded composites was studied by applying 5, 10 and 20 N forces at room temperature. The results showed that the mass loss and the coefficient of friction values are decreased with the addition of CNTs, which is attributed to the increased microhardness and self-lubricating properties of the CNTs.