From CNT dispersion to property enhancement: a comprehensive review on fabrication strategies for Al–CNT composites

Carbon nanotubes (CNTs) have garnered significant interest over the last twenty years due to their remarkable stiffness, strength, aspect ratio, and multifunctionality, rendering them optimal reinforcements for lightweight, high-performance composites in the automotive and aerospace industries. Aluminum and its alloys are particularly well-suited as matrix materials due to their low density, high specific strength, and excellent processability. This paper presents a comprehensive review of advancements in the pre-processing, processing, and post-processing of aluminum–carbon nanotube (Al–CNT) composites, with a specific focus on how CNT distribution affects the ultimate mechanical properties. A critical comparison of pre-processing methods for CNT dispersion and retention, including chemical functionalization, metallic/coated CNTs, ultrasonication-slurry techniques, high-energy ball milling/flake powder metallurgy, and pellet-based feedstock, is conducted, with a focus on CNT structural integrity and interfacial properties. Processing strategies, including casting and powder metallurgy methods, are evaluated with respect to CNT volume fraction, dispersion uniformity, and matrix-CNT interfacial interactions. Subsequent post-processing techniques, including heat treatment, hot isostatic pressing, and deformation-assisted densification, are examined for their contributions to load transfer enhancement. The review emphasises existing obstacles (CNT damage, clustering, interfacial Al₄C₃ formation, scale-up), delineates prospective research avenues, and proposes feasible strategies to advance Al–CNT composites from laboratory demonstrations to commercially viable engineering applications.