An in situ composite of Al (graphite, Al4C3) produced by reciprocating extrusion

A reciprocating extrusion process was used to produce an in situ composite of Al (graphite, Al4C3). 6061 Al alloy powder was first dehydrated at 450°C in vacuum, and then mixed with graphite powder in various volume fractions up to 20%. The mixed powder was hot pressed as a billet and finally consolidated by a reciprocating extrusion machine. Each billet was extruded through the die 15 times. The results show that all the graphite particles were greatly refined and uniformly distributed in the matrix. The graphite in-situ reacted with the Al matrix to form fine dispersed Al4C3 particles both during reciprocating extrusion and subsequent solution treatment. The higher the volume fraction of graphite added to the matrix, and the longer the solution treatment, the harder the composite. The 6061Al-20% (graphite, Al4C3) composite that was solution-treated for 24 h, and then peak aged, could attain a hardness level of 7075-T6 alloy. As for the wear rate, this initially increased due to the presence of the graphite particles; but with higher graphite content and prolonged solution treatment the wear rate subsequently decreased. This phenomenon is attributed to the fact that although the graphite could soften the composites, the Al4C3 strengthened the composites during prolonged solution-treatment time. The wear test demonstrated that composite containing 20% (graphite, Al4C3) which has been solution-treated for 24 h can exhibit an excellent combination of coefficient frictional and wear rates, ∼50 and 70%, respectively, of those of 6061 alloy.