Fabrication And Properties Of6061Al Matrix Composites Reinforced By In-situ Synthesized Carbon Nanotubes

Due to their excellent physical and mechanical properties, carbon nanotubes(CNTs) become the ideal reinforcements for metal matrix composites (MMCs).However, the shortcomings of CNTs including lack of bonding strength and easyagglomeration hamper the development of high-performance composites. In recentyears, our group has developed a method named in-situ chemical vapor deposition(CVD), by which CNTs can be directly synthesised in Al matrix. It remarkablyimproved the dispersion of CNTs and the interfacial bonding properties, and led tobetter utilization of CNTs. In present study,6061aluminum alloy (6061Al) waschosen as matrix based on our previous researches of pure Al matrix. According to thecharacteristic of aluminum alloy powders， a novel approach is developed whichconsists of ball-milling, surface modification, in-situ CVD process and powdermetallurgy to prepare the6061Al-based composites reinforced by In-situ synthesizedCNTs (CNTs/6061Al). The influence of the process on the microstructure andproperties of the composite was investigated.The original6061Al powder was subjected to ball-milling at first. The effect ofball milling parameters on the structure of6061Al powder was investigated. Theresults shows that the plate-shaped6061Al, with a relatively large size (wideness in50μm and thickness around2μm), low impurity, and smooth surface could beobtained when the powders were ball-milled for60min at a speed of500rpm inethanol with powder to ball ratio of1:15. This as-prepared6061Al flake is propitiousto the adsorption of an adhesive.The CNTs/6061Al composite powders were prepared using a certain route consistof modification of an adhesive, adhesion of a catalyst precursor and in-situ synthesisby CVD method. The influence including adhesive types, adhesive concentration,catalyst precursor types, catalyst precursor concentration, et al., on the synthesis ofCNTs and the influence of carbon sources on the microstructure of CNTs wereinvestigate. The in-situ growth mechanism of CNTs in the6061Al matrix wasdiscussed. The results show that, using1wt.%polyvinyl alcohol sol can effectivelymodified the flake powder surface, and the modified powder can adsorb catalyst precursor in the0.05mol/L nickel acetate solution (or cobalt acetate solution) tosynthesis of uniform dispersion of herringbone or straight tubular CNTs by thesubsequent CVD process.CNTs/6061Al composites were fabricated by powder metallurgy including coldpressing, sintering and hot extrusion of the in-situ synthesized composite powders.CNTs content and heat treatment on microstructure and mechanical properties ofCNTs/6061Al composites were discussed. The strengthening mechanism of thecomposites was also discussed. It is found that the compressive yield stress andcompressive elastic modulus of the composites with only1.9wt.%content of CNTswere1.6and0.5times respectively higher than that of unreinforced6061Al. Thecompressive properties of the composites decrease rapidly with the increase of CNTscontent. Meanwhile, the effects of solid solution and aging treatment on CNTs/6061Alwere investigated. It is found the hardness of1.9wt.%CNTs/6061Al compositessubjected to solid solution at530℃for1h and then aging treatment at190℃for3hwas0.82times higher than that of untreated composites.