Process optimization and microstructural analysis of aluminum based composite reinforced by multi-walled carbon nanotubes with various aspect ratios Prozessoptimierung und Mikrostrukturanalyse von mit mehrwandigen Kohlenstoffnanoro ¨ hren versta ¨ rkten Aluminium- Verbundwerkstoffen A. H. Javadi 1 , Sh. Mirdamadi 2 , S. Shakhesi 1 The dispersion of carbon nanostructures in metallic matrix with strong bonding is a very important challenge to achieve a composite with high mechanical properties. In this work, the effect of aspect ratio of reinforcement phase, weight percent and using improved mechanical alloying process and sonication on the well dispersion of multiwalled carbon nanostructures (MWCNTs) were investigated. Moreover, the hot pressing conditions were optimized by factorial design technique to achieve the highest relative density. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray diffraction were used to analyse the microstructure. Also, the particle size of the grain structure of composite con- taining multi-walled carbon nanotubes determined for evaluating the influence of aspect ratio on grain growth. The results verified that by using conventional method of alloying, grinding process and agglomeration of 2 wt% multi-walled carbon nano- tubes with long length can be occurred. By decreasing the weight percent of multi- walled carbon nanotubes to 1 wt%, dispersion process progressed slightly. Short length multi-walled carbon nanotubes showed more clustering and minor damage in both 1 and 2 wt%. By using modified design of alloying (using magnet), both types of multi-walled carbon nanotubes dispersed better than conventional design in the matrix with good bonding at initial times. Keywords: Metal matrix composite / characterization / multiwall carbon nanotube / mechanical alloying / dispersion Schlu ¨ sselwo ¨ rter: Metallmatrix-Verbundwerkstoff / Charakterisierung / mehrwandige Kohlenstoffnanoro ¨ hren / mechanisches Legieren / Dispersion 1 Introduction Recently, composite materials have been widely used be- cause of advanced mechanical and physical properties [1-3]. When lightweight materials with high strength and stiffness, desirability coefficient of thermal expansion and good damping properties are required, metal matrix composites (MMCs) are the best choice [4, 5]. Corresponding author: A. H. Javadi, Department of na- notechnology, Engineering Research Institute, TEH- RAN, IRAN, E-Mail: ah.javadi@srbiau.ac.ir 1 Department of nanotechnology, Engineering Rese- arch Institute, TEHRAN, IRAN 2 Department of materials engineering, science and research branch, Islamic Azad University, TEHRAN, IRAN Mat.-wiss. u. Werkstofftech. 2017, 48, 719–725 DOI 10.1002/mawe.201600495 719 © 2017 WILEY-VCH Verlag GmbH & CO. KGaA, Weinheim www.wiley-vch.de/home/muw