Hot Extrusion of A356 Aluminum Metal Matrix Composite with Carbon Nanotube/Al 2 O 3 Hybrid Reinforcement
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MANY material scientists and engineers have shifted their focus from monolithic materials to composite materials for the development of lightweight, environment-friendly, and high-performance devices. Composite materials are a combination of at least two different materials with a clear interface separating the components. As such, composites are replacing traditional materials because of their relative advantages in terms of higher stiffness and strength. They can have metal or polymer matrices and can be reinforced with continuous fibers, discontinuous fibers/whiskers, or particles.[1–3] Since 1970, carbon fiber reinforcement has been extensively used in a wide array of applications in the automotive, aerospace, and military fields. Carbon nanotubes (CNTs) were discovered by Iijima[4] in 1991. Experiments have shown that CNTs have superior mechanical properties over carbon fibers; e.g., stiffness values up to 1000 GPa, strength on the order of 100 GPa,[5–9] and thermal conductivity of up to 6000 Wm1 K1. Since the discovery of CNTs, many interesting studies on composites with CNTs have been performed. Kondoh et al.[10] considered a magnesium H.H. KIM, Ph.D. Student, and C.G. KANG, Professor, are with the School of Mechanical Engineering, Pusan National University, Busan, South Korea. Contact e-mail: [email protected] J.S.S. BABU, Professor, is with the SRM Research Institute, SRM University, Kattankulathur, Tamil Nadu, India. Manuscript submitted May 6, 2013. Article published online January 28, 2014 2636—VOLUME 45A, MAY 2014
alloy powder composite with carbon nanotubes. They tried to disperse uniformly CNTs in Mg alloy with a zwitterionic surfactant solution. The addition of very small quantities of un-bundled multi-walled multiwalled carbon nanotube (MWCNTs) (0.95 to 1.43 vol pct) to a Mg matrix composite caused a large increase in the tensile strength and yield stress, but a considerable decrease in elongation. Kuzumaki et al.[11] observed a 100 pct increase in tensile strength with 10 vol pct CNT addition. Researchers have tried to introduce 1 to 6.5 vol pct CNTs into an Al-CNT composite material by a powder metallurgy method.[12,13] Al- and Mg-CNT composites were fabricated by Zhou et al.[14] and Uozumi et al.[15] through infiltration of a porous preform. They found that Al(Mg)-CNT composites fabricated through such an infiltration exhibited a good dispersion of CNTs. A review of the literature shows that only limited studies have been carried out on hybrid metal matrix composites (MMCs) using nano/micro-sized reinforcements. Okumus et al.[16] studied the thermal properties of Al-Si/SiC/graphite hybrid MMCs fabricated by squeeze casting. Du and Li[17] evaluated the wearresistance properties of Al2O3/SiC/Al hybrid composites. No systematic attempt has yet been made to study the effects of the hybridization of CNTs and Al2O3 on the mechanical properties of aluminum-based composites, particularly those prepared by the infiltration method. Moreover, resulting mechanical changes in an Al2O3/CNTs/A356 composite, an
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