{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T06:38:44Z","timestamp":1772692724251,"version":"3.50.1"},"reference-count":46,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T00:00:00Z","timestamp":1772496000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Metals"],"abstract":"<jats:p>Hybrid nanocomposites based on Aluminum 6061 (Al 6061) reinforced with carbon nanotubes (CNTs) and aluminum oxide (Al2O3) emerge as promising materials due to their ability to achieve simultaneous improvements in strength, thermal stability, and tribological performance. This study examines the structure\u2013property relationships of CNT\u2013Al2O3 nano-reinforced hybrid Al 6061, with particular emphasis on microstructural evolution and mechanical properties. The nanocomposites are fabricated via a powder metallurgy route, which enables optimized dispersion and homogeneous distribution of CNTs and Al2O3 within the aluminum matrix. Microstructural characteristics, interfacial bonding, and grain refinement are systematically analyzed using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Mechanical characterization demonstrates a marked enhancement in mechanical properties compared to Al 6061. The observed property improvements are attributed to synergistic strengthening mechanisms, including effective load transfer from the matrix to Al2O3 particles, CNT-induced grain refinement, and increased resistance to dislocation motion. These results establish a direct correlation between microstructural features and mechanical performance, highlighting the potential of CNT\u2013Al2O3 reinforced Al 6061 hybrid nanocomposites for lightweight, high-strength applications in aerospace, automotive, and structural engineering industries.<\/jats:p>","DOI":"10.3390\/met16030287","type":"journal-article","created":{"date-parts":[[2026,3,3]],"date-time":"2026-03-03T16:18:45Z","timestamp":1772554725000},"page":"287","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Structure\u2013Property Relationships of CNT\u2013Al2O3 Nano-Reinforced Al 6061 Matrix"],"prefix":"10.3390","volume":"16","author":[{"given":"Beatriz","family":"Monteiro","sequence":"first","affiliation":[{"name":"Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"},{"name":"LAETA\/INEGI-Institute of Science and Innovation in Mechanical and Industrial Engineering, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8615-7612","authenticated-orcid":false,"given":"Aida B.","family":"Moreira","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"},{"name":"LAETA\/INEGI-Institute of Science and Innovation in Mechanical and Industrial Engineering, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4670-4516","authenticated-orcid":false,"given":"S\u00f3nia","family":"Sim\u00f5es","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Faculty of Engineering, University of Porto, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"},{"name":"LAETA\/INEGI-Institute of Science and Innovation in Mechanical and Industrial Engineering, Rua Doutor Roberto Frias, 4200-465 Porto, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Nurguzhin, M., Janikeyev, M., Omarbayev, M., Yermakhanova, A., Meiirbekov, M., Zhumakhanov, M., Keneshbekova, A., Atamanov, M., Akylbayeva, A., and Lesbayev, A. (2025). Structure and Properties of Al\u2013CNT-Based Composites Manufactured by Different Methods: A Brief Review. Materials, 18.","DOI":"10.3390\/ma18010214"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"20240009","DOI":"10.1515\/secm-2024-0009","article-title":"Effect of carbon nanotubes on mechanical properties of aluminum matrix composites: A review","volume":"31","author":"Nie","year":"2024","journal-title":"Sci. Eng. Compos. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"639","DOI":"10.1002\/adem.200700106","article-title":"Novel Nanoparticle-Reinforced Metal Matrix Composites with Enhanced Mechanical Properties","volume":"9","author":"Tjong","year":"2007","journal-title":"Adv. Eng. Mater."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"801","DOI":"10.1515\/rams-2021-0062","article-title":"Recent development in graphene-reinforced aluminium matrix composite: A review","volume":"60","author":"Omar","year":"2021","journal-title":"Rev. Adv. Mater. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"111923","DOI":"10.1016\/j.matdes.2023.111923","article-title":"Interface and strengthening mechanisms of Al matrix composites reinforced with in-situ CNTs grown on Ti particles","volume":"229","author":"Yang","year":"2023","journal-title":"Mater. Des."},{"key":"ref_6","unstructured":"Davis, J.R. (1993). Aluminum and Aluminum Alloys, ASM International."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"2394","DOI":"10.1016\/j.matdes.2006.09.022","article-title":"Carbon nanotube reinforced composites: Potential and current challenges","volume":"28","author":"Esawi","year":"2007","journal-title":"Mater. Des."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1159","DOI":"10.1016\/j.scriptamat.2005.07.022","article-title":"Strengthening in carbon nanotube\/aluminum (CNT\/Al) composites","volume":"53","author":"George","year":"2005","journal-title":"Scr. Mater."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1016\/j.matchar.2017.09.028","article-title":"Microstructure and mechanical characterization of Al6061-CNT nanocomposites fabricated by spark plasma sintering","volume":"133","author":"Najimi","year":"2017","journal-title":"Mater. Charact."},{"key":"ref_10","first-page":"409","article-title":"Reinforcement with carbon nanotubes in aluminum matrix composites","volume":"64","author":"Choi","year":"2011","journal-title":"Scr. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"194","DOI":"10.1016\/j.msea.2008.11.067","article-title":"Synthesis of multi-walled CNT reinforced aluminum alloy composite via friction stir processing","volume":"507","author":"Lim","year":"2009","journal-title":"Mater. Sci. Eng. A"},{"key":"ref_12","first-page":"92","article-title":"Microstructural and mechanical characterization of CNT-reinforced aluminum alloy composites","volume":"607","year":"2014","journal-title":"Mater. Sci. Eng. A"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"5367","DOI":"10.1016\/j.actamat.2006.06.031","article-title":"Investigation of the interfacial reaction between multi-walled carbon nanotubes and aluminum","volume":"54","author":"Ci","year":"2006","journal-title":"Acta Mater."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"108955","DOI":"10.1016\/j.compositesa.2025.108955","article-title":"Enhanced interfacial strength in carbon-nanotubes-reinforced Al matrix composites via an interface substitution strategy","volume":"195","author":"Zhou","year":"2025","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1311","DOI":"10.1016\/j.compositesa.2009.06.004","article-title":"Quantification of carbon nanotube distribution and property correlation in nanocomposites","volume":"40","author":"Bakshi","year":"2009","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"110514","DOI":"10.1016\/j.compositesb.2023.110514","article-title":"Enhanced distribution and mechanical properties of high content nanoparticles reinforced metal matrix composite prepared by flake dispersion","volume":"252","author":"He","year":"2023","journal-title":"Compos. Part B Eng."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/S0924-0136(99)00118-1","article-title":"Metal matrix composites: Production by the stir casting method","volume":"92\u201393","author":"Hashim","year":"1999","journal-title":"J. Mater. Process. Technol."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Mercado-Lemus, V.H., Gomez-Esparza, C.D., D\u00edaz-Guill\u00e9n, J.C., May\u00e9n-Chaires, J., Gallegos-Melgar, A., Arcos-Gutierrez, H., Hern\u00e1ndez-Hern\u00e1ndez, M., Gardu\u00f1o, I.E., Betancourt-Cantera, J.A., and Perez-Bustamante, R. (2021). Wear dry behavior of the Al-6061-Al2O3 composite synthesized by mechanical alloying. Metals, 11.","DOI":"10.3390\/met11101652"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"159","DOI":"10.1016\/j.compositesb.2013.04.051","article-title":"Analysis of dry sliding wear behaviour of Al6061\/SiC\/Al2O3 hybrid metal matrix composites","volume":"53","author":"Umanath","year":"2013","journal-title":"Compos. Part B Eng."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"203","DOI":"10.1016\/S0924-0136(02)00234-0","article-title":"P\/M aluminum matrix composites: An overview","volume":"133","author":"Torralba","year":"2003","journal-title":"J. Mater. Process. Technol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"184653","DOI":"10.1016\/j.jallcom.2025.184653","article-title":"Different mechanical behaviors of nano-Al2O3\/Al composites at room and elevated temperature induced by different phase type","volume":"1045","author":"Chen","year":"2025","journal-title":"J. Alloys Compd."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Samal, P., Raj, H., Meher, A., Surekha, B., Vundavilli, P.R., and Sharma, P. (2024). Synergistic Effect of B4C and Multi-Walled CNT on Enhancing the Tribological Performance of Aluminum A383 Hybrid Composites. Lubricants, 12.","DOI":"10.3390\/lubricants12060213"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"381","DOI":"10.1016\/j.jmatprotec.2004.07.068","article-title":"Production and mechanical properties of Al2O3 particle-reinforced 2024 aluminium alloy composites","volume":"161","author":"Kok","year":"2005","journal-title":"J. Mater. Process. Technol."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Wang, C., Zhu, X., Zhang, K., Liu, J., Xiao, X., Jiang, C., Zhang, J., Lv, C., and Sun, Z. (2025). Microstructures and Mechanical Properties of Al Matrix Composites Reinforced with TiO2 and Graphitic Carbon Nitride. Metals, 15.","DOI":"10.3390\/met15010060"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Salman, K.D., Al-Maliki, W.A.K., Alobaid, F., and Epple, B. (2022). Microstructural Analysis and Mechanical Properties of a Hybrid Al\/Fe2O3\/Ag Nano-Composite. Appl. Sci., 12.","DOI":"10.3390\/app12094730"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.matdes.2009.11.064","article-title":"Processing and microstructural characterization of AA6063 matrix CNT reinforced composites","volume":"31","author":"Toptan","year":"2010","journal-title":"Mater. Des."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1159","DOI":"10.1007\/s42452-025-06918-1","article-title":"Hybrid composites materials of reinforced aluminium alloy and its tribological analysis: A review","volume":"7","author":"Kumar","year":"2025","journal-title":"Discov. Appl. Sci."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"202","DOI":"10.1007\/s42452-025-06532-1","article-title":"Microstructure and toughness characterization of AA6061 hybrid composite reinforced with eucalyptus ash, periwinkle shell, and plantain fiber","volume":"7","author":"Barah","year":"2025","journal-title":"Discov. Appl. Sci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"87","DOI":"10.1016\/j.compositesa.2017.11.013","article-title":"Microstructure and synergistic-strengthening efficiency of CNTs-SiCp dual-nano reinforcements in aluminum matrix composites","volume":"105","author":"Zhang","year":"2018","journal-title":"Compos. Part A Appl. Sci. Manuf."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"113159","DOI":"10.1016\/j.matchar.2023.113159","article-title":"Interfacial structure-property relationship in a carbon nanotube-reinforced aluminum alloy matrix composite fabricated by an advanced method","volume":"203","author":"Nateq","year":"2023","journal-title":"Mater. Charact."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"108952","DOI":"10.1016\/j.diamond.2022.108952","article-title":"Mechanical and wear properties of SiCp\/CNT\/Al6061 hybrid metal matrix composites","volume":"124","author":"Trinh","year":"2022","journal-title":"Diam. Relat. Mater."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"536","DOI":"10.1007\/s11106-024-00416-6","article-title":"Spark Plasma Sintering of Al2O3 Reinforced Aluminum Alloy Metal Matrix Composites (Review)","volume":"62","author":"Iyengar","year":"2024","journal-title":"Powder Metall. Met. Ceram."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Saxena, P., Bongale, A., Kumar, S., and Suresh, R. (2023). Tribological and Hardness Analyses of Friction-Stir-Processed Composites Using the Taguchi Approach. Materials, 16.","DOI":"10.3390\/ma16010420"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"478","DOI":"10.1016\/j.powtec.2021.01.013","article-title":"Compaction behavior and densification mechanisms of CuW composite powders","volume":"382","author":"Peng","year":"2021","journal-title":"Powder Technol."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"12896","DOI":"10.1038\/s41598-020-69341-z","article-title":"Enhanced mechanical and wear properties of Al6061 alloy nanocomposite reinforced by CNT-template-grown core\u2013shell CNT\/SiC nanotubes","volume":"10","author":"Yoo","year":"2020","journal-title":"Sci. Rep."},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Monteiro, B., and Sim\u00f5es, S. (2024). Optimization of Al6061 Nanocomposites Production Reinforced with Multiwalled Carbon Nanotubes. J. Compos. Sci., 8.","DOI":"10.3390\/jcs8090381"},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Monteiro, B., and Sim\u00f5es, S. (2024). Production and Characterization of Hybrid Al6061 Nanocomposites. Metals, 14.","DOI":"10.20944\/preprints202410.0304.v1"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"541","DOI":"10.1007\/s13632-017-0395-0","article-title":"Microstructural and Mechanical Characterization of CNT- and Al2O3-Reinforced Aluminum Matrix Nanocomposites Prepared by Powder Metallurgy Route","volume":"6","author":"Toozandehjani","year":"2017","journal-title":"Metallogr. Microstruct. Anal."},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Haridass, R., Subramani, N., Viknesh, S., Mathan Kumar, M., and Mownitharan, M.S. (2025). Tribological Behavior and Mechanical Characteristics of AL6061 Alloy with Al2O3 and Multi-Walled Carbon Nanotubes Reinforcement Nanoparticles (Hybrid Nano Carbon Tube), SAE. SAE Technical Paper.","DOI":"10.4271\/2024-01-5244"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"20250049","DOI":"10.1515\/jmbm-2025-0049","article-title":"Mechanical and tribological analyses of Al6061-GO\/CNT hybrid nanocomposites by combined vacuum-assisted and ultrasonicated stir casting method","volume":"34","author":"Somayajula","year":"2025","journal-title":"J. Mech. Behav. Mater."},{"key":"ref_41","first-page":"25","article-title":"The cleavage strength of polycrystals","volume":"174","author":"Petch","year":"1953","journal-title":"J. Iron Steel Inst."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"915","DOI":"10.1007\/s40195-021-01306-1","article-title":"Strengthening Mechanisms of 15 Vol.% Al2O3 Nanoparticles Reinforced Aluminum Matrix Nanocomposite Fabricated by High Energy Ball Milling and Vacuum Hot Pressing","volume":"35","author":"Zhao","year":"2022","journal-title":"Acta Metall. Sin."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"43","DOI":"10.1016\/0036-9748(86)90210-3","article-title":"On the strength of discontinuous silicon carbide reinforced aluminum composites","volume":"20","author":"Nardone","year":"1986","journal-title":"Scr. Metall."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"175","DOI":"10.1016\/0025-5416(86)90261-2","article-title":"Dislocation generation due to differences between the coefficients of thermal expansion","volume":"81","author":"Arsenault","year":"1986","journal-title":"Mater. Sci. Eng."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"2769","DOI":"10.1016\/j.actamat.2012.09.036","article-title":"Strengthening mechanisms in a high-strength bulk nanostructured Cu\u2013Zn\u2013Al alloy processed via cryomilling and spark plasma sintering","volume":"61","author":"Wen","year":"2013","journal-title":"Acta Mater."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"5586","DOI":"10.1016\/j.actamat.2010.06.028","article-title":"Orowan strengthening and forest hardening superposition examined by dislocation dynamics simulations","volume":"58","author":"Queyreau","year":"2010","journal-title":"Acta Mater."}],"container-title":["Metals"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2075-4701\/16\/3\/287\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T05:22:24Z","timestamp":1772688144000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2075-4701\/16\/3\/287"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,3]]},"references-count":46,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,3]]}},"alternative-id":["met16030287"],"URL":"https:\/\/doi.org\/10.3390\/met16030287","relation":{},"ISSN":["2075-4701"],"issn-type":[{"value":"2075-4701","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,3]]}}}