Materials Science and Engineering A 385 (2004) 258–266 Characterization of aluminum/graphite particulate composites synthesized using a novel method termed “in-situ powder metallurgy” F. Akhlaghi ∗ , S.A. Pelaseyyed Department of Metallurgy and Materials Engineering, Faculty of Engineering, University of Tehran, P.O. Box 11365-4563, Tehran, Iran Received 29 January 2004; received in revised form 14 June 2004 Abstract In the present study, for the first time a new technique called “in-situ powder metallurgy” has been developed to produce aluminum alloy–graphite (Al/Gr) composites. This method combines the advantages of powder metallurgy (P/M) with those of the stir casting, but avoids at the same time their respective drawbacks. Different percentages (5–15wt.%) of uncoated graphite particles (300–500 m) were introduced to A356 aluminum melt and the slurry was stirred in a specified time–temperature regime resulting in a mixture of aluminum droplets and graphite particles. This blend was cooled in air and the resultant mixture of aluminum and graphite powder particles was then consolidated to produce the final component. In the present method, the typical limitations of stir casting (i.e. poor wettability of graphite with aluminum alloys, flotation and segregation of particles during melt stirring and/or alloy solidification) are absent. Besides, there is no need to prepare the alloy powder particles separately as in the normal P/M methods. The composites exhibited a uniform distribution of graphite particles within the fine grained matrix alloy as well as the improved wear characteristics when compared with the base alloy. © 2004 Elsevier B.V. All rights reserved. Keywords: Particle-reinforced composites; Friction/wear; Scanning electron microscopy; Sintering; Aluminum–graphite composites 1. Introduction Self-lubricating materials offer many improvements over the materials to which lubricant needs to be applied pe- riodically. Among these materials, considerable work has been done on aluminum alloy–graphite particulate compos- ites (Al/Gr MMCs). It has been shown that these light weight MMCs exhibit improvement in mechanical properties [1,2], low friction and wear [3–15], reduced temperature rise at the wearing contact surface [8,16], excellent antiseizure ef- fects [13,15,17,18], improved machinability [9], low thermal expansion and high damping capacity [19–21]. These char- acteristics have made the Al/Gr system a potential candidate for automotive and general engineering applications [4,22]. The processes used to synthesize the Al/Gr composites can be classified into three categories: (i) liquid phase; (ii)solid ∗ Corresponding author. Tel.: +98 21 8012999; fax: +98 21 8006076 E-mail address: fakhlagh@ut.ac.ir (F. Akhlaghi). phase; and (iii) two phase (solid–liquid) routes. It has been documented that the production method has a strong influ- ence on the mechanical and tribological properties of the composite via its effects on the matrix grain size, porosity, the distribution of graphite particles [23] and the interfacial properties of the Al/Gr couple [24]. Although the preparation of such composites by melting and casting routes (i.e. stir casting) is by far the most eco- nomical one, but it is associated with some inherent problems arising mainly from both the apparent non-wettability of graphite by liquid aluminum alloys [25–27] and the density differences between the two materials [28,29]. Therefore, the introduction and retention of graphite particles in the molten aluminum is extremely difficult [30]. Poor wettability and density differences also results in poor recovery of graphite particles in aluminum melt [31], inhomogeneous distribution of the dispersoid [23,29] inadequate bonding between the metal and the graphite particles and formation of porosity at the graphite/matrix interface. Several methods have been 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.06.050