CNT-induced microstructural evolution in Al matrix composite made by additive manufacturing and studying the effect of CNT presence on mechanical and tribological properties

• The microstructure and tribological properties of carbon nanotube reinforced aluminum matrix composites fabricated by SLM were investigated. • The homogenous dispersion of CNT hinder dislocation movement and deformation. • The changes of wear regime is because the formation of a relatively stable mechanically mixed layer with the increase of slide speed. • The predominant wear regime of the reinforced composite is composed of delamination wear and oxidize wear at higher load. • The hardening and stability and thickness of mechanically mixed layer control the wear resistance of the composite. This study investigates the microstructural behaviour and mechanical properties of carbon nanotube (CNT)-reinforced AA2024 aluminum matrix composites fabricated via Selective Laser Melting (SLM), with varying CNT contents of 1, 3, and 5 wt%. As the CNT content increased, the quality of single-track deposits improved, leading to more consistent and continuous weld beads, particularly at 5 wt% CNT. The results demonstrate that CNT reinforcement significantly influences microstructural evolution and enhances the mechanical performance of SLM-processed nanocomposites. Specifically, the 5 wt% CNT/AA2024 composite exhibited refined microstructures, uniform CNT dispersion, improved mechanical properties, and the formation of the Al₄C₃ phase during the SLM process. Wear analysis revealed that increasing sliding speed led to a reduction in wear rate and a transition in wear mechanism—from abrasive to delamination—due to the formation of a stable mechanically mixed layer (MML) that reduced contact between the composite surface and the counter body. Additionally, at higher normal loads, a combined oxidation and delamination wear mechanism became dominant in the CNT-reinforced composites.