Characterization of aluminum/graphite particulate composites synthesized using a novel method termed “in-situ powder metallurgy”

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 (5–15 wt.%) of uncoated graphite particles (300–500 μm) 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.