Pressure infiltration of Al-12Â wt.% Si-X (XÂ =Â Cu, Ti, Mg) alloys into graphite particle preforms

The pressure infiltration of Al and Al-12 wt.% Si-X alloys into preforms of packed graphite particles has been investigated. Compacts were prepared from particles of average diameter of 15, 27, 64, and 124 μm. While infiltration with pure Al at 750 °C was poor due to both gasification of graphite and reaction between C and Al, the lower infiltration temperature used for the Al-Si eutectic alloy improved infiltration performance. Results for the threshold pressure and infiltration kinetics are discussed in the light of previously published results. Ti (up to 1.5 wt.%) and Cu (up to 1.0 wt.%) additions were found to have no effect on pressure infiltration. However, Mg additions (up to 4 wt.%) significantly decreased the threshold pressure, as a consequence of the decrease in surface tension of Al promoted by this element. Coating the graphite particles with a chemical compound that dissolves the oxide layer reduces the threshold pressure, although this has limited technological applicability due to the increase in porosity. The compact permeability derived from infiltration of the alloys is compared with the intrinsic permeability obtained through infiltration of a wetting organic fluid.