TECHNICAL PAPER Synthesis of Nanocrystalline Al 2 O 3 Reinforced Al Nanocomposites by High-Energy Mechanical Alloying: Microstructural Evolution and Mechanical Properties A. Wagih 1 Received: 16 January 2015 / Accepted: 1 May 2015 / Published online: 21 June 2015 Ó The Indian Institute of Metals - IIM 2015 Abstract The scientific importance of nanocomposites is being increased due to their improved properties. In the current paper, the relationship between the reinforcement weight fraction and Tensile properties of Al/Al 2 O 3 (with a reinforcement weight fraction of 0, 2.5, 5 and 10 wt%) synthesized by high energy ball milling is studied. Scan- ning electron microscopy analysis, X-ray diffraction anal- ysis and transmission electron microscopy are used to characterize the produced powder. The results show that the addition of Alumina particles accelerates the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Moreover, Al crystallite size become refined during ball milling of Al powder in the presence of Al 2 O 3 particles. Uniform distribution of nano- sized Al 2 O 3 particles in the Al matrix could be achieved with increase in the reinforcement weight fraction. The microhardness of the composite increases with the increase of the reinforcement weight fraction and it reaches 94 HV at 10 wt% Al 2 O 3 composite. The yield strength and ulti- mate strength of the composite are also increased by increasing the reinforcement weight fraction. Keywords Nanocomposite Á Mechanical milling Á Microhardness Á Mechanical properties 1 Introduction Interest on powder metallurgy (P/M) aluminum metal matrix composites (MMCs) is increasing, since there is a potential field of applications in aerospace, chemical, transportation, structural and automotive industries. P/M aluminum MMCs have improved strength, high elastic modulus, increased wear resistance, low density, and high stiffness over conventional base alloys [1, 2]. High energy ball milling is a simple and useful technique for attaining a homogeneous distribution of the inert fine particles within a fine grained matrix [3]. During ball milling two essential processes occur, cold welding between the different particles and fracturing of the cold welded particles due to high energy collision [4]. The cold welding minimizes the diffusion distance between the atoms of the different components. The fracturing of the welded particles impedes the clustering of the particles promoting the transfer of the high ball collision energy to all particles and produces new, clean surfaces without oxide layers accelerat- ing the diffusion [4, 5]. The most important advantage of this method over other alloying methods is feasibility of addition of alloying elements for improvement of mechanical and physical properties of alloys. Ceramic nano-particles have received great attention owing to their property advantages over conventional coarse grained counterparts [6–8]. Among various rein- forcements, Al 2 O 3 is one of the most widely used disper- soids in Al-based composites. There are some publications about the production of this type of composite using the mechanical milling method. They successfully incorpo- rated microscale Al 2 O 3 particulates in pure Al matrix using the mechanical milling process [9–11]. However, there are only few works on the effect of the addition of nanometric particulates on the structural and morphological behavior of Al powders. & A. Wagih eng_awa2011@yahoo.com; ahmedwagih@zu.edu.eg 1 Mechanical Design and Production Deptartment, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Sharkia, Egypt 123 Trans Indian Inst Met (2016) 69(4):851–857 DOI 10.1007/s12666-015-0570-4