Tribological characterization of Al7075–graphite composites fabricated by mechanical alloying and hot extrusion R. Deaquino-Lara a,b , N. Soltani a , A. Bahrami a,⇑ , E. Gutiérrez-Castañeda c , E. García-Sánchez d , M.A.L. Hernandez-Rodríguez d a Centro de Investigación y de Estudios Avanzados del IPN Unidad Saltillo, Av. Industria Metalúrgica, No. 1062, Parque Industrial, Ramos Arizpe, Coahuila, Mexico b Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, Z.C 31109 Chihuahua, Chihuahua, Mexico c Universidad Autónoma de San Luis Potosí, Instituto de Metalurgia, Av. Sierra Leona 550, Lomas 2da Sección, San Luis Potosí, SLP Z.C 78210, Mexico d Universidad Autónoma de Nuevo León (UANL), FIME-CIDET, Av. Universidad s/n. Cd. Universitaria, San Nicolás de los Garza, NL, Mexico article info Article history: Received 17 September 2014 Accepted 25 November 2014 Available online 3 December 2014 Keywords: Tribological characterization Aluminum alloy Microstructure Mechanical and wear properties Friction coefficient abstract Aluminum matrix composites (AMCs) are candidate materials for aerospace and automotive industry owing to their large elastic modulus, improved strength and low wear rate. A simple method for fabrica- tion of Al7075–graphite composites produced by mechanical alloying (MI) and hot extrusion is described in this paper. Effects of milling time (0–10 h) and graphite concentration (0–1.5 wt.%) on friction, hard- ness and wear resistance of the AMC were investigated. Wear resistance was determined by the pin- on-disk wear method using 20 and 40 N normal loads at a 0.367 m/s sliding velocity. The worn surfaces were examined by scanning electron microscopy (SEM) to identify distinct topographical features for elu- cidation of the prevailing wear mechanisms. Experimental results indicated considerable improvement in AMC hardness and wear resistance by adding 1.5% G (wt.) and 10 h of milling, showing homogenous dis- tribution of the reinforcement particles in the Al-base metal-matrix composite. It was found that abrasion is the dominant wear mechanism in all extruded composites, whilst a combination of adhesion and delamination seems to be the governing mechanism for the 7075 aluminum alloy. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Aluminum-matrix composites (AMC) are materials in which, Al or its alloys, are strengthened by dispersion of hard particles like carbides (Al 4 C 3 , SiC, B 4 C), oxides (Al 2 O 3 ), silicides (Si 3 N4, Mg 2 Si) among others and etc. into the matrix. Thanks to their inherent properties, they can improve mechanical and physical properties of these composites. Recently, particulate reinforced composites (PMMCs) have attracted considerable attention due to their rela- tively low cost and inherent isotropic properties [1–4]. There are several fabrication techniques available to manufacture MMCs, which can be divided in two main types: solid state processes [2,5–7] and liquid state process [8]. In the former, mechanical alloying (MA) and mechanical milling (MM) are generally used to obtain MMCs with excellent mechanical properties, which is possi- ble due to repeatedly flattening, cold welding, fracturing and re- welding of powder particles during high-energy milling. After mill- ing for a certain length of time, steady-state equilibrium is reached when a balance between the rate of welding and the rate of frac- turing is achieved. At this stage each particle contains substantially all of the starting materials, in the proportion they were mixed together [9,10]. Secondary processes and thermo-mechanical pro- cedures such as extrusion, rolling or forging seem to be efficient processes for decreasing the porosity and obtaining a more uni- form particle distribution in such composites [11]. Milling followed by hot extrusion cause less segregation effects and a homogeneous distribution of reinforcement particles into the matrix. Recently, some researchers have demonstrated that employing graphite as reinforcement agent, to produce Al-based composites by mechan- ical milling, increases the mechanical resistance of the composites. Their addition favors refining of powder particle size during mill- ing and promotes mechanical alloying acting as a process control agent (PCA) [2,10,12–16]. Al–graphite composites, also known as self-lubricating composites, have accentuated due to their excel- lent anti-seizure effect, low thermal expansion, high damping capacity, low friction and wear, and reduced rise in temperature at the wearing contact surface [17–19]. This attractive tribological behavior is attributed to the formation of a lubricating film on the http://dx.doi.org/10.1016/j.matdes.2014.11.045 0261-3069/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Ceramics Engineering, Center of Research for Advances Studies of the National Polytechnic Institute, Av. Industria Metalúrgica, No. 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, P.O. BOX 663, Saltillo Z.C 25900, Mexico. Tel.: +52 (844) 176 5492. E-mail address: amin.bahrami@cinvestav.edu.mx (A. Bahrami). Materials and Design 67 (2015) 224–231 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes