Chemically driven interfacial bonding via oxygen for strengthening aluminum matrix composites reinforced with multi-walled carbon nanotubes

Interfacial bonding between aluminum and nanoscale ceramic reinforcements is often weak, limiting the mechanical performance of aluminum matrix nanocomposites (AMNCs) relative to theoretical predictions. This study investigates how incorporated oxygen alters the interfacial structure and bonding chemistry in multi-walled carbon nanotube (MWCNT)-reinforced AMNCs and examines the resulting mechanical response through in-situ tensile testing and nanoindentation. An Al–O/MWCNT composite was fabricated via high-energy ball milling followed by hot rolling, using oxygen-incorporated aluminum powders produced by the gas atomization of an Al–O alloy. The MWCNTs were uniformly dispersed within the matrix, forming distinct interfaces with aluminum. Oxygen enrichment at the interface in the Al-O/MWCNT, revealed by STEM–EDX mapping and line-scan analyses, indicates interfacial bonding mediated by oxygen on both the aluminum and carbon sides. The Al-O/MWCNT composites show a higher fraction of oxygen-related bonds (∼48.5%) compared to Al/MWCNT (∼35.9%), consistent with enhanced Al–O–C interfacial bonding. Correspondingly, the Al–O/MWCNT composite exhibited significant improvements in yield strength (∼12.5%), ultimate tensile strength, ductility, and elastic modulus. Strengthened interfacial bonding promoted more efficient load transfer and delayed interfacial failure under tension, resolving the strength-ductility trade-off in MWCNT-reinforced AMNCs. These findings underscore the pivotal role of oxygen-driven interfacial chemistry in dictating mechanical performance and provide a new interface-engineering route for the design of high-performance aluminum-based nanocomposites.