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Simulation for Carbon Nanotube Dispersion and Microstructure Formation in CNTs/AZ91D Composite Fabricated by Ultrasonic Processing YUANSHENG YANG, FUZE ZHAO, and XIAOHUI FENG The dispersion of carbon nanotubes (CNTs) in AZ91D melt by ultrasonic processing and microstructure formation of CNTs/AZ91D composite were studied using numerical and physical simulations. The sound field and acoustic streaming were predicted using finite element method. Meanwhile, optimal immersion depth of the ultrasonic probe and suitable ultrasonic power were obtained. Single-bubble model was used to predict ultrasonic cavitation in AZ91D melt. The relationship between sound pressure amplitude and ultrasonic cavitation was established. Physical simulations of acoustic streaming and ultrasonic cavitation agreed well with the numerical simulations. It was confirmed that the dispersion of carbon nanotubes was remarkably improved by ultrasonic processing. Microstructure formation of CNTs/AZ91D composite was numerically simulated using cellular automation method. In addition, grain refinement was achieved and the growth of dendrites was changed due to the uniform dispersion of CNTs. DOI: 10.1007/s11663-017-1047-0  The Minerals, Metals & Materials Society and ASM International 2017

I.

INTRODUCTION

MAGNESIUM alloys are of great interest to the automotive and aerospace industries due to their extremely low density. But unsatisfactory strength of magnesium alloys restricts their applications. Adding reinforcements to magnesium alloy to fabricate magnesium composites is an effective way to enhance the strength of magnesium alloys. Among those reinforcements, carbon nanotubes (CNTs) are considered to be good nano-size reinforcements for their excellent properties such as lower density, extremely high elastic modulus, and high strength.[1] Using nano-size reinforcements instead of normal-sized reinforcements can relieve ductility deterioration caused by the addition of reinforcements.[2] Previous research showed that compositing CNTs with magnesium alloy not only enhanced the strength but also improved the ductility of magnesium alloy. For example, the tensile strength of CNTs/AZ91D[3] and CNTs/Mg-6Zn[4] was remarkably enhanced compared with the matrix alloys. And the strength and ductility of CNTs/AZ81 composite were found to be enhanced compared with monolithic AZ81 alloy.[5]

YUANSHENG YANG and XIAOHUI FENG are with the Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China. Contact e-mail: [email protected] FUZE ZHAO is with the Institute of Metal Research, Chinese Academy of Sciences, and also with the University of Chinese Academy of Sciences, Beijing 100049, China. Manuscript submitted November 28, 2016.

METALLURGICAL AND MATERIALS TRANSACTIONS B

Up to now, several methods have been used to fabricate CNTs/Mg composites, such as Disintegrated Melt Deposition (DMD),[6] Powder Metallurgy,[3] and Melt Processing.[7] The most important thing to fabricate CNTs/Mg composites is the dispersion of CNTs in magnesium matrix. Ultr