The effects of graphite and SiC formation on mechanical and wear properties of aluminum– graphite (Al/Gr) composites. E. Gewfiel Mechanical Design and Production Dep. Faculty of Engineering, Zagazig University Zagazig, Egypt M. A. H. EL-Meniawi Materials Engineering Dept. Faculty of Engineering, Zagazig University Zagazig, Egypt Y. Fouad Faculty of Engineering and MaterialsScience. German University in Cairo Abstract— Aluminum–graphite (Al/Gr) composites were fabricated by a proposed technique called “ex-situ and in-situ powder metallurgy” to avoid an interfacial reaction between the graphite and the aluminum. In the present study, a cooled compact pressing of material powders followed by hot extrusion techniques were used. Varies weight percentages of graphite flakes were mixed with Al powder using a mechanical mixing stirrer. The effects of graphite content and SiC formation on microstructures and wear properties of composites were investigated. The SiC particles are formed by in-situ reaction at temperatures above 252 0 C. SiC particles have greatly improved the wear and tensile properties of fabricated composites. The results also showed the SiC particles were refined (< 1μm) and uniformly distributed in the matrices as a result of hot extrusions and little pores were found in the composites. This significantly improves mechanical and wear properties. Keywords— ex-situ and in-situ powder metallurgy, cold pressing, hot extrusion, and wear I. INTRODUCTION Metal Matrix Composites (MMCs) have recently evoked a keen interest for their potential applications in cylinder liners, brake drums, crankshafts, and the aerospace and automotive industries because of their greater strength to weight ratios and high temperature resistances [1]. At the present time, aluminum metal matrix composites (AMMCs) have been well recognized and steadily improved because of their advanced engineering properties, such as their improved wear resistance, low density, specific strength and stiffness [ 2]. The particulate metal-matrix composites are extensively used for tribological applications due to excellent wear resistance especially during sliding. Low density and their ability to carry higher loads give them advantage over their counterparts. The particulate reinforced metal matrix composite has been used to improve the wear resistance. Severe lubrication problems are encountered at high temperature environments where oils and greases cannot be used. Therefore, the need of solid lubricants extensively arises under these extreme conditions. There is an urgent need to develop advanced materials that work with excellent self-lubrication within a wide temperature range.[ 3] . Self-lubricating materials offer many improvements over the materials to which lubricant needs to be applied periodically. Among these materials, considerable work has been done on aluminum alloy–graphite particulate composites (Al/Gr MMCs). The processes used to synthesize the Al/Gr composites can be classified into three main categories: (i) liquid phase; (ii) solid phase; and (iii) two phase (solid–liquid) routes. It has been documented that the production method has a strong influence on the mechanical and tribological properties of the composite via its effects on the matrix grain size, porosity and distribution of graphite particles [4] and the interfacial properties of the Al/Gr couple [5]. In view of this, aluminum alloy–graphite (Al/Gr) particulate composites are being explored for tribological applications. These self- lubricating composites have received attention because of their low friction and wear [6–7], reduced temperature rise at the wearing contact surface [8,9], improved machinability [7], excellent antiseizure effects [10,11], low thermal expansion and high damping capacity [12,13]. Many authors have reported that during dry sliding of the metal/Gr composites, a continuous layer of solid lubricant forms on the tribosurface [14]. The main reasons to produce Al/Gr composite are to increase the strength, stiffness and wear resistance of aluminum or aluminum alloys, but this is usually achieved at the expense of other properties such as ductility. Aluminum and aluminum alloys can be strengthened by dispersing hard particles like carbides, oxides or nitrides into the aluminum matrix by using solid or liquid state techniques . The composites so developed are called ex-situ MMCs. It is reported that agglomeration of reinforcement particulates may occur during processing of most ex-situ composites leading to 978-1-4673-4810-2/12/$31.00 ©2012 IEEE