Fabrication of carbon nanotube reinforced A356 nanocomposites

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Carbon nanotube (CNT) reinforced A356 aluminum alloys cast nanocomposites containing lower CNT contents were successfully fabricated where the way of introducing diluted Al–8 wt% CNT master nanocomposite in A356 melts was used. The differential thermal analysis and x-ray diffraction results showed that aluminum carbide phases (Al4C3) were formed before Al melting. The formation of Al4C3 was then proved to improve the wettability of CNTs during Al melting. Effect of CNT addition on microstructure and mechanical properties of CNTs/A356 nanocomposites were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and universal tensile testing machine. The results showed that CNTs (,0.4 wt%) were well distributed in the CNTs/A356 nanocomposites. CNTs could greatly refine the microstructure of A356 alloy. The mechanical properties of CNTs/A356 nanocomposites were also enhanced by CNT addition. Fractography analysis revealed that CNTs were distributed uniformly throughout the fracture surface.

I. INTRODUCTION

Carbon nanotubes (CNTs) have recently been used in the field of composite materials due to the extraordinary mechanical, thermal, and electrical properties of CNTs. Based on tensile test of single-wall CNTs (SWCNTs), Yu et al.1 found that SWCNTs have a Young’s modulus of ;1 TPa and tensile strength of ;30 GPa. Treacy et al.2 suggested that the tensile strength of multiwall CNTs (MWCNTs) is ;150 GPa, which are much higher than that of SWCNTs. Researches focusing on the fabrication of polymer matrix composites and ceramic matrix composites have been undertaken to obtain the desired properties.3–6 On the other hand, for the metal matrix composites (MMCs), the progress has been rather slow. Zeng et al.7 suggested that one of the remaining challenges to manufacture CNTbased metal composites is to obtain a homogeneous dispersion of CNTs in the matrix. CNTs can easily agglomerate due to the large differences in surface tension and mass density between CNTs and metal matrix.8 Various fabrication methods, such as friction stir processing,9,10 infiltration method,11 semisolid powder processing,12,13 powder metallurgy14–16 and stir-casting process,17,18 have been developed to incorporate CNTs into the aluminum (Al) matrix. Traditionally, powder metallurgy is the favorable method for fabricating metal

Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.258

matrix nanocomposites. However, powder metallurgy is not suitable for large scale production due to its longer processing cycle and higher cost than that of stir-casting process. On the contrary, stir-casting process offers a simple and cheap alterative way to fabricate large scale composites which can be used as billets to manufacture a great variety of products through other processes. Nevertheless, only a few researchers adopted stircasting process mainly because of the following issues: (i) CNTs are lighter than all commercial metals, and not wetted by all